Utility of biochemical markers of bone turnover in the follow-up of patients treated with bisphosphonates

Osteoporosis: Investigations and Monitoring

Background

Osteoporosis is characterized by microarchitectural disruption of the bone, decrease in bone mineral density, and increased skeletal fragility and risk of fracture. Osteoporosis occurs due to the decoupling of bone formation and bone resorption, with a significant increase in resorption. This review article focuses on the role of laboratory investigations in the diagnosis and monitoring of treatment in patients with osteoporosis.

Methods

This review article collected literature from various databases using keywords such as 'Laboratory investigations', 'Osteoporosis', 'Diagnosis', 'Monitoring', and 'Bone turnover markers'.

Results and Discussion

Laboratory investigations, including serum calcium, alkaline phosphatase, vitamin D, and parathormone, are commonly performed tests to exclude secondary causes of osteoporosis and monitor the response to therapy. The biochemical markers of bone turnover are newly emerged tests for monitoring individual patients with osteoporosis. These markers are classified as bone formation and resorption markers, measurable in both serum and urine. The use of these markers is limited by biological and analytical variability. The International Federation of Clinical Chemistry and Laboratory Medicine and the International Osteoporosis Foundation recommend serum procollagen type 1 amino-terminal propeptide as the bone formation marker and β-form of C-terminal cross-linked telopeptide of type I collagen (β-CTx-1/β-CrossLaps) as the marker of choice, using standardized procedures. However, in specific cases, such as patients with chronic renal disease, CTx-1 is replaced by the resorption marker tartrate-resistant acid phosphatase 5b, as its levels are not affected by renal excretion.

Conclusion

Bone turnover markers have emerged as tools for the assessment of osteoporosis, using standardized procedures, and are useful in monitoring therapy and treatment compliance.

Follicle-stimulating hormone is associated with low bone mass in postmenopausal women

We evaluated the influence of two endogenous hormones on bone health in older women. Higher FSH was associated with bone disease, especially in lower estradiol environments. FSH attenuated the relationship between estradiol and bone. This may provide a mechanism through which future clinical research intervenes on bone loss.

INTRODUCTION/PURPOSE

Despite preclinical evidence for an inverse association of follicle-stimulating hormone (FSH) and bone mineral density (BMD), no large epidemiologic studies have evaluated the separate and joint influences of FSH and estradiol on bone in postmenopausal women.

METHODS

In a cross-sectional study of 675 postmenopausal women, we evaluated associations of serum FSH and dual X-ray absorptiometry (DXA)-classified areal BMD as well as low bone mass or osteoporosis (T-score <  - 1.0) of the femoral neck and total hip. We stratified this analysis by serum estradiol (cut at the median). We tested whether FSH mediates the association of estradiol and BMD using the Sobel test.

RESULTS

In linear regression models, there was a significant inverse association of serum FSH with both femoral neck and total hip BMD (both p < 0.01) when adjusted for age, hormone therapy (HT) use, and diabetes. In fully adjusted logistic regression models, women in the highest FSH tertile had higher odds of low bone mass/osteoporosis at the femoral neck (OR = 2.98; 95% CI = 1.86-4.77) and at the total hip (OR = 1.74; 95% CI = 1.06-2.84) compared to those in the lowest FSH tertile. We report evidence of effect modification by estradiol in stratified models and an interaction term. FSH met all criteria of a mediator, including an estimated 70% attenuation of the estradiol-BMD relationship (Sobel p value < 0.001).

CONCLUSIONS

FSH is associated with higher odds of having low bone mass/osteoporosis even after accounting for HT use. FSH is a mediator of the relationship between estradiol and BMD in healthy postmenopausal women. Larger, prospective studies of FSH concentrations and bone health are needed.

Bone union after spinal fusion surgery using local bone in long-term bisphosphonate users: a prospective comparative study

Bisphosphonates are the most commonly used drugs for osteoporosis and long-term use of bisphosphonates may affect fusion rate after spinal fusion surgery. There was significant delayed union after 6 months in long-term bisphosphonates users; however, there were no significant difference in fusion rate of long-term bisphosphonate users. Therefore, spinal fusion surgery should not be hesitated in long-term bisphosphonates users.

PURPOSE

Bisphosphonates (BPs) are the most popular class of drugs for treatment of postmenopausal osteoporosis. Long-term use of BPs may also inhibit the spinal fusion process after posterior lumbar interbody fusion (PLIF). We compared bone fusion rates of long-term BPs users and non-users after undergoing spinal fusion surgery.

METHODS

A total of 97 postmenopausal women who were candidates for single-level PLIF were recruited from 2015 to 2016. Participants were divided into two groups, with 63 patients in a long-term BPs user group and 34 patients in a non-user group. Serum C-terminal cross-linking telopeptide (CTX) levels were checked for bone resorption markers. Bone fusion rates were calculated at 6 months and 1 and 2 years after the surgery. Clinical outcomes were measured using the Oswestry Disability Index (ODI) and visual analog scale (VAS).

RESULTS

Serum CTX level was dramatically decreased in the long-term BPs user group (p < 0.05). Fusion rates at 6 months after surgery were 42% in the non-user group and 26% in the long-term BPs user group (p = 0.035). However, fusion rates were 82% in the long-term BPs user group and 87% in the non-user group at 2 years after surgery (p > 0.05). There was no significant difference between the two groups in ODI or VAS.

CONCLUSIONS

Even though there was significant delayed union after 6 months in long-term BPs users, at the 2-year postoperative follow-up, there was no significant difference in bone fusion rate between the two groups. Long-term BPs users showed fusion rates greater than 80% and clinical outcome improvements that were comparable to those in non-users. No significant effect on fusion rate after PLIF was found in long-term BPs users.

Bisphosphonate guidelines for treatment and prevention of myeloma bone disease

Multiple myeloma (MM) is a haematological malignancy characterised by the clonal proliferation of plasma cells in the bone marrow. More than 80% of patients with MM display evidence of myeloma bone disease (MBD), characterised by the formation of osteolytic lesions throughout the axial and appendicular skeleton. MBD significantly increases the risk of skeletal-related events such as pathologic fracture, spinal cord compression and hypercalcaemia. MBD is the result of MM plasma cells-mediated activation of osteoclast activity and suppression of osteoblast activity. Bisphosphonates (BP), pyrophosphate analogues with high bone affinity, are the only pharmacological agents currently recommended for the treatment and prevention of MBD and remain the standard of care. Pamidronate and zoledronic acid are the most commonly used BP to treat MBD. Although generally safe, frequent high doses of BP are associated with adverse events such as renal toxicity and osteonecrosis of the jaw. As such, optimal duration and dosing of BP therapy is required in order to minimise BP-associated adverse events. The following guidelines provide currently available evidence for the adoption of a tailored approach when using BP for the management of MBD.

Calcium and Bone Metabolism Indices

Calcium and inorganic phosphate are of critical importance for many body functions, thus the regulations of their plasma concentrations are tightly controlled by the concerted actions of reabsorption/excretion in the kidney, absorption in the intestines, and exchange from bone, the major reservoir for calcium and phosphate in the body. Parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D (1,25(OH)₂D) control calcium homeostasis, whereas PTH, 1,25(OH)₂D, and bone-derived fibroblast growth factor 23 (FGF 23) control phosphate homeostasis. Hypoparathyroidism can cause hypocalcemia and hyperphosphatemia, whereas deficient vitamin D actions can cause osteomalacia in adults and rickets in children. Hyperparathyroidism, alternatively, can cause hypercalcemia and hypophosphatemia. Laboratory tests of calcium, phosphate, PTH, and 25-hydroxyvitamin D are very useful in the diagnosis of abnormalities associated with calcium and/or phosphate metabolisms. Bone is constantly remodeled throughout life in response to mechanical stress and a need for calcium in extracellular fluids. Metabolic bone diseases such as osteoporosis, osteomalacia in adults or rickets in children, and renal osteodystrophy develop when bone resorption exceeds bone formation. Bone turnover markers (BTM) such as serum N-terminal propeptide of type I procollagen (P1NP) and C-terminal collagen cross-link (CTX) may be useful in predicting future fracture risk or monitoring the response to anti-resorptive therapy. There is a need to standardize sample collection protocols because certain BTMs exhibit large circadian variations and tend to be influenced by food intakes. In the United States, a project to standardize BTM sample collection protocols and to establish the reference intervals for serum P1NP and serum CTX is ongoing. We anticipate the outcome of this project to shine lights on the standardization of BTM assays, sample collection protocols, reference intervals in relation to age, sex, and ethnic origins, and clinical utilities of BTMs. This review will briefly discuss the regulations of calcium and phosphate homeostasis, laboratory's role in the diagnosis, and monitoring of bone and calcium metabolism, as well as the usefulness and controversies of the utilities of BTMs in the diagnosis and monitoring of metabolic bone diseases.

Serum N-terminal telopeptide of type I collagen as an early marker of fracture nonunion in rabbits

The aim of the present study was to establish an experimental animal model of fracture nonunion, and to investigate the changes in serum biomarker concentrations in fracture nonunion. A total of 20 purebred New Zealand rabbits were divided into two group: A bone defect group and a bone fracture group. In the bone defect group, a 15-mm section of bone (including the periosteum) was removed from the mid-radius, and the medullary cavities were closed with bone wax. In the bone fracture group, the mid-radius was fractured. X-rays were taken and blood samples were collected preoperatively and at 2, 3, 4, 5, 6, 7, 8, 10 and 12 weeks after the surgical procedure. The serum concentrations of osteocalcin (OC) and bone-specific alkaline phosphatase (BSAP) served as markers of bone formation, and those of C-terminal telopeptide of type I collagen (CTX), N-terminal telopeptide of type I collagen (NTX) and tartrate-resistant acid phosphatase 5b (TRACP 5b) served as markers of bone resorption. The concentration levels of the markers were measured using a biotin double-antibody sandwich enzyme-linked immunosorbent assay. In the bone defect group, bone callus was observed on X-ray at 2 weeks in three rabbits and the bone calluses stabilized at 5 weeks; however, none of the bones had healed at 8 weeks. In the bone fracture group, the fracture line was distorted at 2 weeks and bone calluses formed at 6-8 weeks. In the bone defect group, the serum BSAP and TRACP 5b concentrations increased following the surgical procedure, peaked at 4 weeks, began to decrease at 5 weeks and stabilized after 6 weeks. The serum OC concentrations did not change significantly following the surgical procedure. The serum CTX concentrations fluctuated during the first 4 weeks, peaked at 5 weeks, then decreased and stabilized after 6 weeks. The serum NTX concentrations fluctuated during the first 4 weeks, were significantly lower at 5 weeks compared with the other time points and stabilized after 6 weeks. These results suggested that a bone nonunion model can be established in New Zealand rabbits by resecting a 15-mm section of bone from the mid-radius prior to bone wax blocking. Measurement of the serum BSAP, CTX, NTX, and TRACP 5b concentrations may be useful for the early detection of bone nonunion. The serum NTX concentrations changed significantly in rabbits with bone nonunion. Further studies are required in order to determine the feasibility of using serum NTX concentrations for the early diagnosis of bone nonunion.

N-terminal telopeptides of type I collagen and bone mineral density for early diagnosis of nonunion: An experimental study in rabbits

BACKGROUND

The diagnosis and treatment of bone nonunion have been studied extensively. Diagnosis and treatment of nonunion are mainly performed based on the interpretation of clinico-radiographic findings, which depend on the clinician's experience and the degree of bone callus formation during the fracture-healing process. However, resolution may be compromised when the bone mineral content is <25%. A feasible method of monitoring bone-healing is therefore needed. We monitored a rabbit model of bone nonunion by regular radiographic examinations, QCT detection, and biomarker concentrations.

MATERIALS AND METHODS

Twenty purebred New Zealand rabbits (10 male and 10 female, 5-6 months of age, 2.5-3.0 kg) were divided into bone defect Group (I) that 10 left radius bones underwent resection of 1.5 cm of mid-radius bone and bone fracture Group (II) that another 10 left radius bones underwent only mid-radius fracture. Quantitative computed tomography detection of bone mineral density (BMD) and serum markers of bone formation (osteocalcin [OC], bone-specific alkaline phosphatase) and bone resorption (C- and N-terminal telopeptides of type I collagen (NTX) and tartrate-resistant acid phosphatase 5b) were assayed. There are twenty rabbits (10 male and 10 females). The age was 5-6 months weighing 2.5-3.0 kg). The defect was created in middle 1/3 radius in 10 rabbits and fracture was created in middle 1/3 radius of 10 rabbits.

RESULTS

BMD and NTX concentrations were significantly lower at 5 weeks postoperatively compared to the preoperative values and were significantly different between the two groups. OC showed no significant difference before and after surgery.

CONCLUSIONS

BMD and NTX concentrations may be useful for early detection of bone nonunion in rabbits.

Measurement of urinary N-telopeptides and serum C-telopeptides from type I collagen using a lateral flow-based immunoassay

Measuring bone turnover markers could detect early stages of osteoporosis and early responses to anti-osteoporotic treatments. Currently, commonly used bone turnover markers, N-telopeptides (NTx) and C-telopeptides (CTx), are measured using ELISA tests, which demands time and increases cost. Bone turnover markers need to be measured more easily for general use. Lateral flow-based immunoassay would be an appropriate method for this context. This study was performed to investigate the precision of a newly developed lateral flow-based immunoassay for measuring the urinary NTx and serum CTx, and their correlations with ELISA measurements. Urine NTx and serum CTx concentrations were determined by photoscan of newly developed strips, using a lateral flow-based immunoassay for 36 subjects (mean age 66.2 years, SD 7.5 years; four males and 32 females). Repeated measurement of urinary NTx and serum CTx were performed three times, using this technology for a precision test. The correlation of the lateral flow-based immunoassay with the ELISA measurements was analyzed. Precision of the newly developed lateral flow based immunoassay was 0.974 (ICC, 95% confidence interval, 0.955 to 0.986) and 0.995 (ICC, 95% confidence interval, 0.991 to 0.997) for urinary NTx and serum CTx, respectively. The correlation of lateral flow based immunoassay with ELISA was 0.913 for urinary NTx and 0.872 for serum CTx. These results suggest that measuring the urinary NTx and serum CTx, using a lateral flow-based immunoassay, is a relevant method for point-of-care testing and screening of bone resorption markers.

Bone turnover markers in patients with type 1 Gaucher disease

Bone complications occur frequently in Gaucher disease (GD) and reduce the quality of life of these patients. Skeletal involvement is an important indication for treatment to ameliorate symptoms and reduce the risk of irreversible and debilitating disease. Bone biomarkers have been used to assess disease status and the response to therapy in a number of bone disorders. Here, we examine the literature for evidence of abnormalities in bone turnover markers in patients with type 1 GD to assess whether they might be useful for the assessment of bone involvement in GD. We have found that bone biomarkers in GD show highly variable results which do not currently support their routine use for clinical assessment of bone status, as an indication for therapy initiation, or for monitoring the response to therapy. A greater understanding of bone markers and their relation to the bone manifestations of GD is required.

Emerging concepts in the management and treatment of osteonecrosis of the jaw

Since the first description of bone necrosis in patients receiving bisphosphonate therapy in 2004, there have been multiple retrospective, prospective, and case-control studies that have served to characterize the diagnosis, associated risk factors, and treatment of this new complication. Bisphosphonate-related osteonecrosis of the jaw is at present associated with several risk factors that are identified across several disciplines in medicine and dentistry. With this level of broad-based recognition, new clinical and basic science research initiatives have begun and are likely to elucidate the etiopathogenesis of this disease process, significantly improving the level of disease management and prevention.

Serum bone resorption markers after parathyroidectomy for renal hyperparathyroidism: correlation analyses for the cross-linked N-telopeptide of collagen I and tartrate-resistant acid phosphatase

Patients on long-term dialysis may develop secondary hyperparathyroidism (SHPT) with increased serum concentrations of bone resorption markers such as the cross-linked N-telopeptide of type I collagen (NTX) and type-5b tartrate-resistant acid phosphatase (TRAP). When SHPT proves refractory to treatment, parathyroidectomy (PTX) may be needed. Renal patients on maintenance HD who received PTX for refractory SHPT (n = 23) or who did not develop refractory SHPT (control subjects; n = 25) were followed prospectively for 4 weeks. Serum intact parathyroid hormone (iPTH), NTX, TRAP, and bone alkaline phosphatase (BAP) concentrations were measured serially and correlation analyses were performed. iPTH values decreased rapidly and dramatically. BAP values increased progressively with peak increases observed at 2 weeks after surgery. NTX and TRAP values decreased concurrently and progressively through 4 weeks following PTX. A significant correlation between TRAP and NTX values was observed before PTX but not at 4 weeks after PTX. Additionally, the fractional changes in serum TRAP were larger than those in serum NTX at all times examined after PTX. Serum iPTH, TRAP, and NTX values declined rapidly following PTX for SHPT. Serum TRAP values declined to greater degrees than serum NTX values throughout the 4-week period following PTX.

Current recommendations for laboratory testing and use of bone turnover markers in management of osteoporosis

Osteoporosis is a major health problem worldwide, and is projected to increase exponentially due to the aging of the population. The absolute fracture risk in individual subjects is calculated by the use of algorithms which include bone mineral density (BMD), age, gender, history of prior fracture and other risk factors. This review describes the laboratory investigations into osteoporosis which include serum calcium, phosphate, creatinine, alkaline phosphatase and 25-hydroxyvitamin D and, additionally in men, testosterone. Parathyroid hormone (PTH) is measured in patients with abnormal serum calcium to determine its cause. Other laboratory investigations such as thyroid function testing, screening for multiple myeloma, and screening for Cushing's syndrome, are performed if indicated. Measurement of bone turnover markers (BTMs) is currently not included in algorithms for fracture risk calculations due to the lack of data. However, BTMs may be useful for monitoring osteoporosis treatment. Further studies of the reference BTMs serum carboxy terminal telopeptide of collagen type I (s-CTX) and serum procollagen type I N-terminal propeptide (s-PINP) in fracture risk prediction and in monitoring various treatments for osteoporosis may help expedite their inclusion in routine clinical practice.

A systematic review of microsurgical reconstruction of the jaws using vascularized fibula flap technique in patients with bisphosphonate-related osteonecrosis

Objective

The aim of this systematic review was to assess the role of microsurgical reconstruction of the jaws in patients with bisphosphonate-related osteonecrosis, and biological complications after an observation period of at least 12 months.

Material and methods

An electronic MEDLINE search supplemented by manual searching was conducted to identify studies reporting data of at least 12 months observation on the microsurgical reconstruction of the jaws in patients with bisphosphonate-related osteonecrosis.

Results

Four studies resulted eligible for the analysis yielded. Three out of five studies were free of complications, with a success rate of 100% as no recurrence of osteonecrosis was registered.

Conclusions

Microsurgical reconstruction of the jaws represents a valid treatment modality in patients with bisphosphonate-related osteonecrosis at 3^rd stage of the disease.

Consensus on the utility of bone markers in the malignant bone disease setting

Biochemical markers of bone turnover provide insight into ongoing rates of skeletal metabolism and tumor-bone interactions in patients with malignant bone disease. This article reviews the available recent evidence assessing the potential of bone markers for detecting and monitoring malignant bone lesions in patients with advanced cancers, and for assessing overall skeletal health and response to antiresorptive therapies in patients at all stages of cancer progression. Most data thus far are for urinary N-terminal cross-linked telopeptide of type I collagen (NTX) in predicting risks of skeletal morbidity and death and monitoring response to zoledronic acid in patients with bone metastases. Ongoing studies are evaluating such correlations for other markers and therapies. Emerging evidence suggests that bone markers may help identify patients at high risk for bone metastasis or bone lesion progression, thereby allowing improved follow-up. Results from ongoing clinical trials evaluating such potential applications of bone markers are awaited.

Bone disease in HIV infection: a practical review and recommendations for HIV care providers

Low bone mineral density (BMD) is prevalent in human immunodeficiency virus (HIV)-infected subjects. Initiation of antiretroviral therapy is associated with a 2%-6% decrease in BMD over the first 2 years, a decrease that is similar in magnitude to that sustained during the first 2 years of menopause. Recent studies have also described increased fracture rates in the HIV-infected population. The causes of low BMD in individuals with HIV infection appear to be multifactorial and likely represent a complex interaction between HIV infection, traditional osteoporosis risk factors, and antiretroviral-related factors. In this review, we make the point that HIV infection should be considered as a risk factor for bone disease. We recommend screening patients with fragility fractures, all HIV-infected post-menopausal women, and all HIV-infected men ⩾50 years of age. We also discuss the importance of considering secondary causes of osteoporosis. Finally, we discuss treatment of the more severe cases of bone disease, while outlining the caveats and gaps in our knowledge.

Bisphosphonate-related osteonecrosis of the jaw: an overview

Bisphosphonates are widely used in the management of metastatic disease to bone and in diseases of altered bone turnover. Recently, multiple-case series and retrospective studies have established a relationship between necrotic bone lesions localized to the jaw and the use of chronic bisphosphonate therapy. This condition has been named bisphosphonate-related osteonecrosis of the jaw (BRONJ). To evaluate the potential risks associated with this new and emerging complication, stage-specific management strategies and guidelines have been developed. In view of the widespread use of chronic bisphosphonate therapy, the observation of an associated risk of osteonecrosis of the jaw should alert practitioners to monitor for this previously unrecognized complication and to reevaluate the indications for and the duration of bisphosphonate therapy in patients with osteopenia/osteoporosis and cancer. Morbidity associated with BRONJ might be prevented or reduced by implementing prevention strategies and establishing early diagnostic procedures. The current widespread use of bisphosphonates as an inhibitor of bone resorption is directly attributable to their efficacy in improving the quality of life for patients with metastatic bone cancer, osteoporosis, and Paget's disease.

Reconstruction of defects caused by bisphosphonate-induced osteonecrosis of the jaws

Reconstructive surgery of defects for any disease or injury including bisphosphonate-induced osteonecrosis of the jaws requires an understanding of the pathophysiology of the condition. Related to bisphosphonates, it is the apoptosis (programmed cell death) of the osteoclast that inhibits, and in some cases stops, bone renewal/remodeling altogether. Therefore, reconstruction begins with a debridement of resection considering this mechanism. For intravenous bisphosphonate-induced osteonecrosis defects of the mandible, most resections are immediately reconstructed with a rigid titanium plate provided that secondary infection is controlled, there is sufficient soft tissue present, and a resection margin containing variable bone marrow can be achieved. For some similar defects with significant secondary infection, a delayed rigid plate placement after the recipient site has healed and is infection free represents another option. In those defects in which there is a significant soft tissue loss, flap reconstruction may also be necessary. The pectoralis major myocutaneous flap is the most predictable and most commonly used flap, followed by the trapezius myocutaneous flap, and stemocleidomastoid flap. Bone graft reconstructions are rarely needed, and are often not indicated due to minimal benefit for the patient, anesthetic risks, or active cancer at metastatic sites. However, in selected cases, mostly for breast cancer or prostate cancer patients with continuity defects from intravenous bisphosphonate-induced osteonecrosis, standard cancellous marrow grafting with platelet-rich plasma growth factor supplementation has been successful. Maxillary resections are treated with prosthodontic obturators as they are in primary cancer surgery. Reconstruction of oral bisphosphonate-induced osteonecrosis defects usually takes the form of alveolar grafting and/or dental implant placements, and only rarely requires grafting of continuity defects. Standard grafting techniques and dental implant placements can be used if guided by the published serum C-terminal telopeptide (CTX) test. The guidelines are less than 100 pg/mL = high risk, 100 pg/mL to 150 mg/mL = moderate risk, and greater than 150 pg/mL = minimal risk.

The effects of Acanthopanax senticosus extract on bone turnover and bone mineral density in Korean postmenopausal women

The purpose of this prospective randomized study was to investigate the effects of the extract of Acanthopanax senticosus (AS extract), a widely used oriental herb, on bone remodeling and bone mineral density in Korean postmenopausal women. A total of 81 postmenopausal women with osteopenia or osteoporosis, an age of less than 65 years, were enrolled in the study. Subjects were randomly assigned to two groups: (1) the control group (n = 40), calcium intake (500 mg per day), and (2) the treatment group (n = 41), calcium (500 mg per day) plus AS extract (3 g per day). After treatment with AS extract for 6 months, the AS extract group showed a significant increase in serum osteocalcin levels compared with the control group (P = 0.041). However, no significant changes in bone mineral density were observed by dual-energy X-ray absorptiometry (DXA). AS extract was generally well tolerated, and no differences were observed between the two groups in terms of adverse events. This study suggests that AS extract supplementation may have beneficial effects on bone remodeling in Korean postmenopausal women and that it has no significant adverse events.

Utility of biochemical markers of bone turnover and bone mineral density in management of osteoporosis

Biochemical markers of bone turnover (bone-turnover markers) are released during bone formation or resorption and can be measured in blood and/or urine. The concentration of bone-turnover markers in serum or urine reflect bone remodeling activity and can potentially be used as surrogate markers of the rate of bone formation or bone resorption. While the diagnosis of osteoporosis is based on bone mineral density (BMD), the absolute fracture risk for a particular BMD measurement varies several fold depending on age and is also influenced by other clinical risk factors. The measurement of bone-turnover markers may be of additional value to BMD and clinical risk factors in fracture risk assessment by improving the sensitivity and specificity of prediction of future fractures. In clinical practice, bone-turnover markers may help make cost-effective treatment decisions in patients with borderline absolute risk. BMD changes following treatment cannot be detected with confidence for 12-24 months due to measurement imprecision. Bone-turnover markers, which show an early response following treatment, may be useful for monitoring therapy, identifying non-compliance and non-responders, and predicting early response to therapy. This review concludes by identifying the need for internationally agreed-upon standards for bone resorption and formation.

The use of bone markers in a 6-week study to assess the efficacy of oral clodronate in patients with metastatic bone disease

Biochemical markers of bone metabolism are strongly associated with skeletal complications in metastatic bone disease. The bisphosphonate clodronate reduces skeletal morbidity by inhibiting bone resorption. This study investigated the use of bone markers to assess the efficacy of oral clodronate across a range of clinically relevant doses. There were 125 patients with metastatic bone disease randomized to daily oral clodronate (800, 1,600, 2,400 and 3,200 mg) or placebo in a double-blind, multicenter study. Urinary N-terminal telopeptide of type I collagen (U-NTX), serum C-terminal telopeptide of type I collagen (S-CTX), urinary calcium (U-Ca), and bone alkaline phosphatase were measured weekly for a 6-week treatment period. Doses of >or=1,600 mg clodronate produced mean reductions of >40% in U-NTX, S-CTX and U-Ca, all significantly different from placebo (P=0.0015, 0.001, 0.0036, respectively), after 6 weeks. Evaluation of least significant changes in markers suggested that the commonly used 1,600 mg dose was most appropriate for breast cancer patients. However, this dose was suboptimal for other (mainly prostate cancer) patients, who showed better response to 2,400 mg. The number of adverse events in the treatment arms was not significantly different from that in placebo, but a higher number of patients had diarrhea in the 3,200 mg arm and withdrew from the study. This trial is the first to explore the dose-response relationship of clodronate in oncology using specific markers of bone turnover. It has confirmed that the 1,600 mg dose is safe and effective for breast cancer patients but may be suboptimal for the other tumors studied.

Looking beyond low bone mineral density: multiple insufficiency fractures in a woman with post-menopausal osteoporosis on alendronate therapy

Insufficiency fractures occur most commonly in the pelvic girdle and in the sacrum, followed by the tibia and the femoral neck. Insufficiency fractures of the femoral diaphyses are rare, with only few reported cases in the literature. The strongest associations exist with untreated osteoporosis. We describe an unusual case of multiple insufficiency fractures in a 73-yr-old Chinese woman who presented with a 10-month history of bilateral groin pain and difficulty with walking in the absence of trauma, diagnosed 18 months following the commencement of anti-resorptive therapy with alendronate. The pathogenesis of such insufficiency fractures is poorly understood, but next to low bone mineral density and micro-architectural damage likely involves other components such as changes in bone turnover and patient-related factors (e.g. non-compliance). This case report and review of the literature draws attention to some of the challenges in the diagnosis and management of such rare insufficiency fractures.

The diagnosis and treatment of osteoporosis in men on androgen deprivation therapy for advanced carcinoma of the prostate

PURPOSE

Androgen deprivation therapy (ADT) for advanced prostate cancer increases the risk of osteoporosis. Thus, the practicing urologist should be aware of the appropriate assessment and management. In this article we review the tests designed to diagnose osteoporosis as well as treatment options. We also review methods to monitor the response to therapy and make recommendations for management.

MATERIALS AND METHODS

We performed a MEDLINE (1966 to 2004) search for the terms male, osteoporosis, bone mineral density, prostate cancer, androgen deprivation therapy, bisphosphonates, estrogen and the combinations thereof. We then constructed a management algorithm based on the best evidence available.

RESULTS

Dual energy x-ray absorptiometry of the hip is the gold standard test for osteoporosis. Biochemical markers of bone turnover are not suitable for diagnosis but they have been shown to be useful for monitoring the response to treatment. Smoking cessation, weight bearing exercise, and vitamin D and calcium have been shown to help improve bone mineral density (BMD). Bisphosphonates have been demonstrated to increase BMD and decrease fracture risk in men with osteoporosis. Estrogens have also recently been shown to decrease bone turnover and increase BMD in men on ADT.

CONCLUSIONS

Hip dual energy x-ray absorptiometry should be performed in all men who are anticipated to be on long-term ADT. In addition, all men on ADT should receive vitamin D and calcium supplementation, and perform regular weight bearing exercise. The value of smoking cessation cannot be overstated. In men who have osteopenia or osteoporosis bisphosphonate therapy should be initiated. Estrogen therapy has shown promise but specific recommendations cannot be made at this time.

A randomized controlled trial of calcium with vitamin D, alone or in combination with intravenous pamidronate, for the treatment of low bone mineral density associated with Crohn's disease

BACKGROUND

Osteoporosis is a common complication of Crohn's disease.

AIM

To study the effect on the bone mineral density of a bisphosphonate (pamidronate) given intravenously, in combination with oral calcium and vitamin D supplements, compared with oral calcium and vitamin D supplements alone.

METHODS

Seventy-four patients with Crohn's disease and low bone mineral density at the lumbar spine and/or hip were randomized to receive either a daily dose of 500 mg of calcium with 400 IU of vitamin D alone or in combination with four three-monthly infusions of 30 mg of intravenous pamidronate over the course of 12 months. The main outcome measure was the change in bone mineral density at the lumbar spine and hip, measured by dual X-ray absorptiometry, at baseline and 12 months.

RESULTS

Both groups gained bone mineral density at the lumbar spine and hip after 12 months. There were significant (P < 0.05) changes in the pamidronate group, with gains of + 2.6%[95% confidence interval (CI), 1.4-3.0] at the spine and + 1.6% (95% CI, 0.6-2.5) at the hip, compared with gains of + 1.6% (95% CI, - 0.1-3.2) and + 0.9% (95% CI, - 0.4-2.1) at the spine and hip, respectively, in the group taking vitamin D and calcium supplements alone.

CONCLUSIONS

In patients with Crohn's disease and low bone mineral density, intravenous pamidronate significantly increases the bone mineral density at the lumbar spine and hip.

Abnormalities in bone mineral density and bone histology in thalassemia

This study demonstrated that there was extensive iron staining on trabecular surface and marked reduction in trabecular bone volume without significant alteration in bone formation and bone resorption rates as well as significant reduction in bone mineral density in 18 thalassemic patients. Serum IGF-I was reduced and may modulate the reduction of bone mass.

INTRODUCTION

Bone histomorphometric studies in thalassemia to show alterations in bone histology and their relationship to biochemical parameters are very limited. Therefore, this study was systematically conducted to determine the alterations in thalassemia patients.

METHODS

Serum biochemical parameters, trans-iliac crest bone biopsy, and determination of bone mineral density of femur and lumbar spine were done in 18 thalassemic patients (10 females and 8 males).

RESULTS

Serum osteocalcin, carboxy terminal teleopeptide fragment of type I collagen, and parathyroid hormone levels were within normal limits, but serum 25(OH) vitamin D (19.3 +/- 1.6 ng/ml) and 1,25(OH)2 vitamin D (33.77 +/- 1.51 pg/ml) levels were decreased. Serum insulin-like growth factor I (IGF-I; 145.2 +/- 20 ng/ml) was suppressed, whereas serum ferritin (1366.6 +/- 253.9 ng/ml) was markedly elevated. Reduced bone mineral density was found in all studied areas. Trabecular bone volume was significantly decreased (16.65 +/- 1.12%), whereas bone formation rate, eroded surface, and other bone histomorphometric parameters were within normal limits. The trabecular bone volume varied significantly with bone mineral density of total femur (r = 0.48, p = 0.04). There was an extensive stainable iron surface on the mineral front (9-60%). Significant correlation between serum IGF-I, serum ferritin, stainable iron surface, and bone mineral density, lumbar spine, and total femur were found. Serum IGF-I correlated with trabecular bone volume (r = 0.6, p = 0.03), inversely with both serum ferritin level (r = -0.6, p < 0.01), and inversely with stainable iron surface (r = -0.53, p = 0.02). Multiple regression analysis demonstrated that IGF-I was the only independent variable that determined bone mineral density of lumbar spine and total femur.

CONCLUSION

Low bone mineral density and reduced trabecular bone volume with extensive iron deposition are the predominant findings in thalassemic patients. There was no evidence of increased bone resorption or mineralization defect. A reduction in circulatory IGF-I may modulate the reduction of bone mass.

Radiotherapy in conjunction with intravenous infusion of 180 mg of disodium pamidronate in management of osteolytic metastases from breast cancer: clinical evaluation, biochemical markers, quality of life, and monitoring of recalcification using assessments of gray-level histogram in plain radiographs

PURPOSE

To evaluate the clinical improvement and radiographically monitor the effect of local radiotherapy in conjunction with disodium pamidronate (DP) on metastatic osteolytic disease.

METHODS AND MATERIALS

Thirty-three patients with osteolytic metastasis from advanced breast cancer received radiotherapy with a 6-MV linear accelerator up to a dose of 30 Gy (3 Gy/fraction, 5 d/wk) combined with 24 monthly sessions of a 180-mg DP infusion. Conventional X-rays were obtained during the first six sessions of DP treatment, retaining the same settings for each exposure. The analysis of the image attributes was based on measuring the first-order statistics of the mean value and energy of gray-level histograms in the osteolytic region.

RESULTS

The 6-month measurements compared with baseline showed statistically significant differences (p < 0.01, Wilcoxon test) in energy of gray-level histogram (-10.8%), mean value of gray-level histogram (+9.5%), pain score (-5.8 points), Eastern Cooperative Oncology Group status (-2.4 points), urine hydroxyproline/creatinine ratio (-41.7%), urine calcium/creatinine ratio (-58.8%), and bone alkaline phosphatase (-42.4%). Quality of life as determined by the European Organization for Research and Treatment of Cancer Core Quality of Life Questionnaire (version 3) also improved. During follow-up, 88% of patients had complete and 12% partial responses (International Union Against Cancer radiologic criteria). On multivariate analysis, greater changes in the mean value of the gray-level histogram and negative nodal status were predictors for a reduction in the number of skeletal complications after therapy. Flu-like syndrome occurred in 13 patients (39%) and was well managed with mild antipyretics.

CONCLUSION

Image-processing in plain radiographs offers an objective way to assess recalcification. The image-processing indexes, along with the measurements of performance status, quality of life, and biochemical markers, improved significantly. Local radiotherapy combined with long-term high-dose DP up to 180 mg is tolerable and has a high therapeutic response.

Pamidronate is superior to ibandronate in decreasing bone resorption, interleukin-6 and beta 2-microglobulin in multiple myeloma

OBJECTIVES

Bisphosphonates have been found to reduce skeletal events in patients with multiple myeloma (MM). This is the first randomised trial to compare the efficacy of pamidronate and ibandronate, a third-generation aminobisphosphonate, in bone turnover and disease activity in MM patients.

METHODS

Patients with MM, stage II or III, were randomly assigned to receive either pamidronate 90 mg (group I: 23 patients) or ibandronate 4 mg (group II: 21 patients) as a monthly intravenous infusion in addition to conventional chemotherapy. Skeletal events, such as pathologic fractures, hypercalcaemia, and bone radiotherapy were analysed. Bone resorption markers [N-terminal cross-linking telopeptide of type-I collagen (NTX) and tartrate-resistant acid phosphatase type 5b (TRACP-5b)], bone formation markers (bone alkaline phosphatase and osteocalcin), markers of disease activity (paraprotein, CRP, beta 2-microglobulin), and interleukin-6 (IL-6) were also studied.

RESULTS

In both groups, the combination of chemotherapy with either pamidronate or ibandronate produced a reduction in bone resorption and tumour burden as measured by NTX, IL-6, paraprotein, CRP, and beta 2-microglobulin from the second month of treatment, having no effect on bone formation. TRACP-5b also had a significant reduction in the pamidronate group from the second month of treatment and in the ibandronate group from the sixth month. However, there was a greater reduction of NTX, IL-6, and beta 2-microglobulin in group I than in group II, starting at the second month of treatment (P = 0.002, 0.001, and 0.004, respectively) and of TRACP-5b, starting at the fourth month (P = 0.014), that being continued throughout the 10-month follow-up of this study. There was no difference in skeletal events during this period. A significant correlation was observed between changes of NTX and changes of TRACP-5b, IL-6, and beta 2-microglobulin from the second month for patients of both groups.

CONCLUSIONS

These results suggest that a monthly dose of 90 mg of pamidronate is more effective than 4 mg of ibandronate in reducing osteoclast activity, bone resorption, IL-6, and possibly tumour burden in MM. TRACP-5b has also proved to be a useful new marker for monitoring bisphosphonates treatment in MM.

Diurnal, week-to-week, and long-term variation in urine deoxypyridinoline cross-link excretion in healthy older women

OBJECTIVES

To establish a reference range for morning and afternoon excretion of urinary deoxypyridinoline (DPD) in apparently healthy older women selected from a volunteer database. To assess the extent of diurnal variation and short and long-term within-subject longitudinal variation.

DESIGN

Prospective, observational, cohort study.

SETTING

Clinical Age Research Unit, King's College School of Medicine, London, United Kingdom.

PARTICIPANTS

Forty-two women aged 68 to 89 (median age 75) selected from a volunteer database.

METHODS

Subjects completed an osteoporosis risk factor questionnaire and a physical examination and had a measurement of the broadband ultrasound attenuation and speed of sound of their right heel. Subjects provided six urine samples: morning and afternoon at baseline and 1 week and 60 weeks later for measurement of DPD.

RESULTS

The mean baseline values for DPD of morning and afternoon samples were 7.2 nM/mM and 6.0 nM/mM creatinine, respectively. The majority of subjects showed diurnal variation, with mean afternoon values 15% lower than morning values (P <.0001 for afternoon vs morning values). The mean difference in DPD after 60 weeks was 1.67 nM/mM for morning and 1.34 nM/mM for afternoon creatinine. This difference was not significant. Some individuals displayed marked changes in DPD excretion with no change in health status or treatment. DPD excretion in a nonfasting afternoon sample showed similar characteristics to morning void samples in terms of scatter, week-to-week variation, and long-term reproducibility.

CONCLUSIONS

The study was set up to provide background data to assist the development of a clinical osteoporosis service for older women. Further studies are needed to determine whether these measurements predict fracture risk and respond to treatment changes in this age group.

Changes in bone turnover following gonadotropin-releasing hormone (GnRH) agonist administration and estrogen treatment in cynomolgus monkeys: a short-term model for evaluation of antiresorptive therapy

In this study we determine the early time course of estrogen deficiency-induced bone loss in the cynomolgus monkey and examine the potential of this method for evaluating antiresorptive therapies. In two groups of animals, estrogen deficiency was induced by the administration of a gonadotropin-releasing hormone agonist (GnRHa) and bone turnover was measured using biochemical markers. Two weeks after receiving GnRHa, serum estradiol decreased to below the detection limit in most animals and remained there through 6 months or until estrogen replacement started (months 4-6). Relative to untreated animals, urinary deoxypyridinoline (dPyr), as well as C- and N-telopeptides of type I collagen, were significantly elevated 4 weeks after receiving GnRHa. Serum osteocalcin increased in GnRHa-treated animals as early as week 4 and the level was significantly higher than in untreated control animals from weeks 8-24. Estradiol treatment returned all measures of bone turnover to control levels within 2 weeks. The use of biochemical markers as surrogates of bone turnover and loss was validated by measurement of bone mineral density (BMD), which showed a significant reduction at 6 months in estrogen-deficient animals. However, lumbar BMD in animals that received GnRHa and estradiol was similar to that in animals that had not received GnRHa. In conclusion, a monthly depot injection of GnRHa resulted in increased bone turnover due to estrogen deficiency, as early as 4 weeks after treatment. Estrogen administration returned bone turnover to control levels in 2 weeks. This method represents a valid model for evaluating antiresorptive agents in the short term in a nonhuman primate. Furthermore, the data suggest that changes in biochemical markers in response to antiresorptive therapy in humans may be detectable at much earlier timepoints than commonly used.

Pamidronate increases markers of bone formation in patients with multiple myeloma in plateau phase under interferon-alpha treatment

Bisphosphonates are potent inhibitors of osteoclastic activity and reduce the disease-related skeletal complications when they are used in combination with chemotherapy in patients with multiple myeloma (MM). Pamidronate also inhibits apoptosis of primary osteoblastic cells and probably induces apoptosis on human MM cells and osteoclasts. It has been reported that interferon-alpha (IFN-alpha) decreases bone resorption and that low doses of IFN-alpha result in a significant increase in serum osteocalcin (OSC). The aim of this study was to determine the effects of pamidronate treatment on biochemical markers of bone resorption [cross-linked N-telopeptides of type I collagen (NTx)], bone formation [bone alkaline phosphatase (BAP) and OSC], disease activity [beta2-microglobulin, CRP, paraprotein], and interleukin-6 (IL-6) in patients with MM in plateau phase under IFN-alpha maintenance. The above parameters were evaluated in 28 patients (13 M, 15 F, median age 70 years) during maintenance treatment, before the addition of pamidronate and after 1, 3, 6, 9, 12, and 14 months of the combined therapy. The addition of pamidronate to maintenance treatment resulted in a significant reduction of NTx, IL-6, beta2-microglobulin, CRP from the 3rd month and paraprotein from the 6th month of treatment, whereas BAP and OSC were significantly increased from the 6th month. These changes continued during the 14-month follow-up of the combined treatment. Multivariate analysis showed a significant negative correlation between changes of BAP and OSC and the patients' age. The greater increase of the bone formation markers was observed in younger patients. These results suggest that, in addition to the inhibition of osteoclastic activity, pamidronate in combination with IFN-alpha was shown to induce bone formation in patients with MM in the plateau phase.

Prevention of secondary osteoporosis postmenopause in hemiplegia

OBJECTIVES

To study secondary osteoporosis postmenopause in women with hemiplegia and to show the therapeutic effects of etidronate and how osteoporotic conditions relate to the activities of daily living (ADL).

DESIGN

Eighty-one postmenopausal women with hemiplegia were admitted within 6 mo of their first cerebrovascular accident. The bone mineral density (BMD) and biochemical markers of bone turnover were measured at the time of admission. Forty women (treatment group) received a 2-wk administration of etidronate. Forty-one women (control group) were not administered etidronate.

RESULTS

After completing a 3-mo rehabilitation program, BMD levels were remeasured. ADL was evaluated by FIM. The low ADL group had a larger decrease in BMD than the high ADL group. For the control group, the BMD rate of change on the paretic side of the femoral neck was -9.6%/3 mo for the low ADL group. BMD loss was reduced significantly by the administration of etidronate for the low ADL group.

CONCLUSIONS

Results indicate that ADL corresponds to the progression of osteoporosis in postmenopausal women with hemiplegia and that increasing the level of ADL will reduce the progression of osteoporosis. Use of etidronate has also been proven to have a suppressive effect on the BMD decrease in women.

Correlations between biochemical markers of bone resorption and creatinine excretion

There were two reasons for doing this study. The first was to assess whether expressing biochemical markers of bone resorption as a ratio to creatinine excretion influences the correlations between them. The second was to assess whether biochemical markers of bone resorption are correlated with creatinine excretion, which is a biomarker of muscle mass. Three biochemical markers of bone resorption, free deoxypyridinoline (DPD), N-telopeptides (NTx) and C-telopeptides (CTx), together with creatinine (cr), were measured in 24-h urine samples of 45 healthy people (26 women and 19 men). The urinary concentrations of DPD, NTx and CTx were highly correlated with each other. These relationships were weakened, or no longer statistically significant, when the markers were expressed as a ratio to cr excretion. The 24-h excretion of each of the markers was correlated with 24-h cr excretion in men, but only 24-h DPD was correlated with 24-h cr excretion in the women. The men had significantly higher 24-h excretion rates of each of the markers than the women did. Since muscle mass is related to skeletal mass, these data suggest that in healthy people the rate of bone resorption may be a function of skeletal size as well as the rate of bone turnover. For small human studies 24-h urine sampling is recommended in preference to untimed sampling. However, for clinical purposes, or for large clinical trials, this may not be practical.

Early response in biochemical markers predicts long-term response in bone mass during hormone replacement therapy in early postmenopausal women

Based on data from 153 early postmenopausal women who completed a double-blind, randomized 3 year study of graded hormone replacement therapy (HRT) doses or placebo, we investigated the value of bone markers to predict prevention of bone loss. Absolute values of serum and urinary CrossLaps (S-CTX and U-CTX) after 2 weeks of treatment were significantly correlated to 3 year bone mass response (r = -0. 28/-0.35; p < 0.001). These associations were fully expressed at 6 months (r = -0.61/-0.64; p < 0.001). Receiver operating characteristic analyses revealed that the predictive capacity of one measurement of a resorption marker after 6 months' treatment performed similarly as assessment of hip bone mass over 3 years in predicting preservation of spinal bone mass over 3 years. Comparable results were obtained using percent change from baseline in resorption markers at both 6 and 12 months, whereas for formation markers percent change was superior to absolute value at 6 months but not at 12 months. Values of accuracy for S-CTX for a cutoff of 1881 pmol/L at 6 months were 85.2% (sensitivity), 74.3% (specificity), 90.5% (positive predictive value), and 63.4% (negative predictive value); U-CTX performed similarly, whereas the values for the formation markers were slightly lower. A cutoff for S-CTX of 1245 pmol/L eliminated false-positive individuals (those who had a decrease below the cutoff but lost bone). In the false-negative group, which was composed of individuals whose S-CTX did not decrease below the cutoff but had preserved bone mass, S-CTX was significantly associated with spinal bone mass response (r = -0. 41; p < 0.01), indicating these women had been treated with a dose that was not at its optimum for their individual bone turnover. For this cutoff, the values were 49.5% (sensitivity), 97.1% (specificity), 98% (positive predictive value), and 40% (negative predictive value). In conclusion, early bone marker measurements predict long-term preservation of bone mass during HRT. Resorption markers seem superior to formation markers, which reflects that the primary effect of HRT is on bone resorption. A strategy with two cutoff levels may optimize the use of bone markers to predict bone mass response. Whether resorption markers can be used to guide individualized treatment remains to be investigated.

The role of bone turnover markers and risk factors in the assessment of osteoporosis and fracture risk

The clinical evaluation of osteoporosis in individual patients involves confirmation of the diagnosis, the investigation of secondary causes of osteoporosis and the evaluation of subsequent fracture risk. Optimum clinical assessment involves bone mineral densitometry with the treatment thresholds modified by clinical risk factors for individual patients. Bone turnover markers and clinical risk factors can be used to identify patients at risk of osteoporotic fracture and those who have secondary osteoporosis. Risk assessment should involve the evaluation of absolute rather than relative risk. Further work is required to improve the integration of clinical risk factors, bone turnover markers and bone densitometry into appropriate models to enable the assessment of the absolute risk of fracture for individual patients.

Proteolysis of human bone collagen by cathepsin K: characterization of the cleavage sites generating by cross-linked N-telopeptide neoepitope

An immunoassay for cross-linked N-telopeptides of type I collagen (NTx) in urine or serum has proven to give a sensitive index of osteoclast-mediated bone resorption. We show that recombinant human cathepsin K is highly active in releasing the NTx neoepitope in 100% yield from bone type I collagen. Cathepsins S, L, and B were also active but at 57%, 36%, and 27% of the yield of K, respectively. The matrix metalloproteinases that were tested, stromelysin, collagenase 3, or matrilysin, did not produce any immunoreactivity. Cathepsin K also acted on demineralized bone matrix, releasing NTx epitope and completely dissolving the bone particles in 24-48 h. Proteolytic cleavage of a G-L peptide bond in the alpha2(I)N-telopeptide was shown to be required for recognition by monoclonal antibody 1H11. Peptide analysis identified bonds in the N-telopeptide and helical cross-linking domains adjacent to the cross-linking residues at which cathepsin K cleaved in bone collagen. The sites were consistent with the known substrate specificity of cathepsin K, which prefers a hydrophobic residue or proline in the critical P2 position. The NTx peptides generated by cathepsin K were of low molecular weight, in the range previously found in human urine. Because cathepsin K appears to be essential for the normal resorption of mineralized bone matrix by osteoclasts, these findings help explain the specificity and responsiveness of NTx as a marker of osteoclastic bone resorption in vivo.

Clinical Utility of Biochemical Markers of Bone Remodeling

Remodeling is essential for bone health. It begins with resorption of old bone by osteoclasts, followed by the formation of new bone by osteoblasts. Remodeling is coupled (formation is linked to resorption). After middle age or perhaps beginning earlier, bone loss occurs because resorption exceeds formation. This imbalance is accentuated by estrogen deficiency as well as by many diseases and conditions. Biochemical markers that reflect remodeling and can be measured in blood or urine include resorption markers (e.g., collagen cross-links) and formation markers (e.g., alkaline phosphatase).

Bone markers exhibit substantial short-term and long-term fluctuations related to time of day, phase of the menstrual cycle, and season of the year, as well as diet, exercise, and anything else that alters bone remodeling. These biological factors, in addition to assay imprecision, produce significant intra- and interindividual variability in markers.

Bone marker measurements are noninvasive, inexpensive, and can be repeated often. Unfortunately, most of the studies that provided insight on clinical situations did not focus on markers as a primary endpoint. Bone markers have been useful in clinical practice and have been helpful in understanding the pathogenesis of osteoporosis and the mechanism of action of therapies. In clinical trials, markers aid in selecting optimal dose and in understanding the time course of onset and resolution of treatment effect. Clinical questions that might be answered by bone markers include diagnosing osteoporosis, identifying “fast bone losers” and patients at high risk of fracture, selecting the best treatment for osteoporosis, and providing an early indication of the response to treatment. Additional information is needed to define specific situations and cut points to allow marker results to be used with confidence in making decisions about individual patients.

Bone markers in clinical practice

Although biologic indices of bone turnover are widely accepted as research tools in population-based studies, their clinical utility in the management of the individual patient remains controversial. Their main limitation for a routine clinical use is related to an important biologic variability, which means that large variations (ie, in response to therapy) are needed to consider a difference between two measurements as reflecting a significant biologic change. To date, the most valuable bone markers are serum osteocalcin, bone-specific alkaline phosphatase, and the N-terminal propeptide of type 1 procollagen for bone formation and urinary measurements of the phenazopyridine crosslinks and related telopeptides for bone resorption. New serum assays for both C-telopeptide and N-telopeptide of type 1 collagen seem promising but need extensive validation. Although bone markers provide little information in the diagnosis of osteoporosis, strong evidence now shows that they can predict, albeit imperfectly, the rate of bone loss in menopausal women and the response to some antiresorptive therapies. In some populations, increased bone turnover has been shown to be a strong predictor of fracture risk, independently and to the same extent as low bone density. Whether bone markers are used to monitor the efficacy of (or compliance with) a specific treatment or to identify patients at risk for osteoporosis and thus to target preventive therapy, cost-benefit analysis, and evaluation of the potential improvement in patient outcome are clearly needed before these parameters may be universally accepted as tools to optimize patient care.

Biochemical markers of bone turnover

Biochemical markers of bone turnover that are specific to bone allow study of the subtle changes in bone turnover associated with osteoporosis. They have been evaluated in Paget's disease of the bone and chronic renal failure. This review focuses on the use of biochemical markers of bone turnover in osteoporosis. The data in this review period are numerous and varied due to the growing interest in the use of biochemical markers of bone turnover in clinical practice. The data provide support for the use of the newer bone turnover markers for monitoring treatment of osteoporosis, if care is taken to minimize sources of variability.

Practical clinical application of biochemical markers of bone turnover: Consensus of an expert panel

Biochemical markers of bone turnover have emerged as powerful tools to aid in managing osteoporosis. The newer bone markers have been intensively studied for more than a decade. As a result, we can now confidently report their clinical utility in assessing risk of rapid bone loss and fracture, and monitoring therapy in postmenopausal women with or at risk of osteoporosis. In this review, we will provide a comprehensive foundation for this utility. While there are still questions remaining to be answered, bone marker technology has matured to play an essential role in patient management. We will describe, in practical terms, how bone markers can be appropriately incorporated into clinical practice today.