The validity of biochemical markers in metabolic bone disease in preterm infants: a systematic review

Effects of two-stage preterm formulas on growth, nutritional biomarkers, and neurodevelopment in preterm infants

Background

Formula-fed preterm infants require nutrient-enriched formulas with optimized protein levels to support growth and neurodevelopment. The purpose of this study was to evaluate the safety, tolerability, and effectiveness of a new liquid two-staged formula system designed to provide tailored nutrition during hospital stay and after discharge.

Methods

Male and female very-low-birth-weight preterm infants (birth weight ≤1,500 g; gestational age ≤32 weeks) were recruited from three neonatal units in Poland and Slovakia in a prospective, open-label, interventional study. Stage 1 formula providing 3.6 g intact protein/100 kcal was consumed from enrollment until reaching 1,800 g, followed by a post-discharge (PD) Stage 2 formula with 2.8 g/100 kcal protein, which was consumed for 30 days. Weight gain velocity (WGV in g/kg/day) between the first day of achieving full enteral feeding (FEF D1 rate of 150 ml/kg/day and cessation of parenteral feeding) and day reaching 1,800 g was compared to the minimally required WGV (15 g/kg/day) for non-inferiority (primary endpoint), and to the Fenton median growth rate for superiority (17.3 g/kg/day), adjusting for sex, gestational age, site, visit, and WGV. Changes in z-scores, feeding tolerance, nutritional biomarker status, and safety were also assessed from FEF D1 to 30 days PD. In an observational follow-up at 2 years of age, neurodevelopment was evaluated using the Bayley Scales of Infant and Toddler Development (BSID-III).

Results

Adjusted weight gain velocity (95% CI) between the first day of full enteral feeding and day reaching 1,800 g in per protocol (PP, N = 18) was 23.0 (20.1-25.9) g/kg/day; lower limit of the 95% CIs exceeded the non-inferiority margin (15 g/kg/day, p < 0.001) and the superiority margin (17.3 g/kg/day, p < 0.001). Mean stool frequency ranged from 2.5 to 3.3 stools per day. The two-stage formula supported adequate growth patterns throughout the study and nutritional biomarkers of protein and mineral status were within normal ranges. At 24 months corrected age, the mean ± SD of the BSID cognitive scale was 97.3 ± 13.9 in PP, with all infants achieving a score >70. None of the adverse events reported were related to the study formulas.

Conclusion

The two-stage preterm formulas supported postnatal weight gain, adequate growth, cognitive development within normal ranges, and a safe profile of protein and bone biomarkers.

Clinical Trial Registration

Clinicaltrials.gov registration, NCT03728764, NCT04962035.

Role of fibroblast growth factor-23 as an early marker of metabolic bone disease of prematurity

PURPOSE

Metabolic bone disease of prematurity (MBDP) remains a significant cause of morbidity in extremely premature newborns. In high-risk patients, suspected diagnosis and subsequent treatment modifications, with limitations in terms of sensitivity and specificity, rely on low phosphorus levels and/or high levels of alkaline phosphatase (ALP). We investigated the potential of fibroblast growth factor-23 (FGF23) as an early marker for MBDP when measured at 3-4 weeks of life in at-risk patients.

METHODS

A single-center prospective observational non-interventional study including preterm newborns of both sexes, with a gestational age of less than 32 weeks and/or a birth weight of less than 1500 g. In the standard biochemical screening for MBDP performed between 3 and 4 weeks of life within a nutritional profile, the determination of FGF23 was included along with other clinical and metabolic studies. The study was conducted at Marqués de Valdecilla University Hospital in Santander, Spain, from April 2020 to March 2021. Participants provided informed consent. Biochemical analyses were conducted using various platforms, and follow-up evaluations were performed at the discretion of neonatologists. Patients at high risk for MBDP received modifications in treatment accordingly. The sample was descriptively analyzed, presenting measures of central tendency and dispersion for continuous variables, and absolute numbers/percentages for categorical ones. Tests used included t-tests, Mann‒Whitney U tests, chi-square tests, logistic regressions, Pearson correlation, and ROC curve analysis (IBM SPSS Statistics version 19). Significance level: P < 0.05.

RESULTS

In the study involving 25 at-risk premature newborns, it was found that 20% (n = 5) were diagnosed with MBDP. Three of these patients (60%) were identified as high-risk based on standard biochemical evaluation at 3-4 weeks of age, while the other two patients (40%) were diagnosed in subsequent weeks. However, in all 5 patients, measurement of FGF23 levels would allow for early identification and optimization of treatment before other markers become altered. Low levels of FGF23 at 3-4 weeks, even with normal phosphorus and ALP levels, indicate the need for modifications in nutritional supplementation.

CONCLUSIONS

MBDP remains a significant concern in extremely premature newborns. Current diagnostic methods rely on limited biochemical markers. Early detection of low FGF23 levels enables timely interventions, potentially averting demineralization.

Diagnostics of Metabolic Bone Disease in Extremely Preterm Infants-Clinical Applicability of Bone Turnover Biochemical Markers and Quantitative Ultrasound

BACKGROUND

Significant improvement in neonatal care has enabled increasing survival of preterm infants. Metabolic bone disease of prematurity is often overlooked due to other comorbidities of preterm birth. The best approach is screening and prevention of the disease in high-risk infants such as preterm infants.

AIM

We followed up the clinical, radiological, and serum biochemical markers of metabolic bone disease in extremely preterm infants (<28 weeks of gestation). The clinical applicability and validation of C-terminal telopeptide of type I collagen (CTX-I) as a novel bone turnover marker were assessed. Standard and novel biochemical bone turnover markers and quantitative ultrasound were compared.

METHOD

Patients' data were collected from medical records. Assessments of calcium, phosphate, alkaline phosphatase, bone-alkaline phosphatase, CTX-I, and quantitative ultrasound were prospectively performed twice in 42 extremely preterm infants at postmenstrual ages of 30-32 weeks and 36-40 weeks. Bone mineral density was measured by quantitative ultrasound.

CONCLUSION

Phosphate, alkaline phosphatase, bone alkaline phosphatase, calcium, or ionized calcium are not related to gestational age, but bone mineral density, measured by quantitative ultrasound, is related. There is no correlation between standard and novel biochemical markers and quantitative ultrasound for the identification of metabolic bone disease.

Neurodevelopment Outcomes in Very-Low-Birth-Weight Infants with Metabolic Bone Disease at 2 Years of Age

Metabolic bone disease (MBD) predominantly affects preterm infants, particularly very-low-birth-weight (VLBW) infants weighing <1500 g. However, there are limited reports on MBD and neurodevelopmental outcomes. This study aimed to analyze the risk factors for MBD and understand its impact on neurodevelopmental outcomes at 2 years of corrected age. Overall, 749 VLBW infants weighing <1350 g at birth were enrolled. Exclusion criteria were major congenital abnormalities, chromosomal abnormalities, and loss of follow-up on the Bayley Scales of Infant Development, Third Edition (BSID-III) test at 24 months of corrected age. Infants were retrospectively assessed by a trained case manager using the BSID-III test at 6, 12, and 24 months old. Infants were categorized as with or without MBD according to radiographic signs. Of those enrolled, 97 VLBW infants were diagnosed with MBD, compared to 362 VLBW infants without MBD. The proportion of infants that completed three follow-ups was 86%. At the assessment at 2 years of age, infants with MBD had lower and more significant differences in motor, language, and cognitive composites. MBD is associated with poor neurodevelopmental outcomes in cognitive, motor, and language composites for VLBW infants at 24 months of corrected age.

Early elevated alkaline phosphatase as a surrogate biomarker of ongoing metabolic bone disease of prematurity

Very low birth weight (VLBW) neonates present a high risk of metabolic bone disease (MBD). Our main objective was to determine the easiest way to make an early diagnosis of this disease by identifying surrogate biomarkers before any radiological signs occurred. We conducted in our NICU a 6-month observational prospective study, with inclusion of all singleton VLBW neonates. We collected clinical and biological data, and nutritional intakes during hospitalization. We defined biological MBD (bMBD) as alkaline phosphatase (ALP) levels superior to 600 UI/L at day of life 30 (DOL30) and performed a case-control analysis. Nine out of 30 patients (30%) exhibited bMBD. All have extremely low birth weight and were significantly younger in gestational age (GA) and smaller at birth. There was no statistically significant difference in nutritional intake between bMBD and control groups. In the bMBD group, phosphatemia was lower since DOL3. ALP was already significantly higher at DOL15, and way beyond normal range.

CONCLUSIONS

Our results showed that even the strict respect of nutritional guidelines cannot completely prevent bMBD in high-risk patients and suggest that an early screening from DOL15, with ALP levels greater than 500 UI/L, could be sufficient for detection of upcoming MBD.

WHAT IS KNOWN

• Metabolic bone disease of prematurity (MBD) definition is not consensual, but biological changes appear earlier than radiological signs of rickets. • MBD management relies on biological evidence. Treatment is based on phosphate and/or calcium and calcitriol supplementation.

WHAT IS NEW

• Studying phosphocalcic biological assessment in very low birth weight neonates, we showed respect of nutritional guidelines could not protect from biological MBD. • Increase in alkaline phosphatase (ALP), about 500 UI/l at day of life 15, could be a biomarker of MBD with no need of X-ray evaluation and sufficient to begin a treatment to prevent osteopenia.

Clinical Phenotypes of Malnutrition in Young Children: Differential Nutritional Correction

This review article summarizes current data on malnutrition etiology and pathogenesis in infants. Topical requirements for revealing this condition, its diagnosis and severity assessment via centile metrics are presented. The characteristics of the most common clinical phenotypes of postnatal growth insufficiency in infants (premature infants with different degree of maturation, including patients with bronchopulmonary dysplasia) are described. Differential approaches for malnutrition nutritional correction in these children are presented. The final section of the article describes special nutritional needs for children with congenital heart defects in terms of hemodynamic disorders nature and severity. Modern nutritional strategies for preparation of these patients to surgery and for their postoperative period are presented. The use of high-calorie/high-protein product for malnutrition correction in the most vulnerable patients with described in this review phenotypes is worth noticing.

Are we undertreating calcium deficiency in metabolic bone disease of prematurity? A case report and review

BACKGROUND

Both calcium (Ca) and phosphorus (P) are needed to prevent and treat metabolic bone disease (MBDP). However, the predominant focus of many treating neonatologists lies in supplementing P and vitamin D. In this report, we describe a VLBW infant with severe MBDP due to inadequately treated calcium deficiency and discuss the need to recognize this entity.

CASE DETAILS AND MANAGEMENT

A 25-week, 700 gm baby boy had chronic lung disease and necrotizing enterocolitis. He received total parenteral nutrition, budesonide, furosemide, and caffeine. With high serum alkaline phosphatase (ALP: 1,700 IU/L) and low P (2.8 mg/dl), MBDP was diagnosed at 12 weeks, started on oral phosphate, human milk fortifier, and 1,400 IU/d of vitamin D before discharge. He was readmitted 2 weeks later with decreased lower limb mobility and respiratory distress. X-rays revealed severe osteopenia and fractures of both femurs. Serum P was 4.6 mg/dl but ALP was high (1,700 IU/L), and Ca was low (6.4 mg/dl). Parathyroid hormone (PTH: 605 pg/ml) and 25-hydroxy Vitamin D (25 OHD > 200 ng/ml) were very high. We discontinued his P and vitamin D, hypocalcemia treated with IV Ca gluconate, later oral Ca citrate, and calcitriol. Phosphate was added after normalization of Ca. Over the next many weeks, X-rays and biochemistry improved.

DISCUSSION

MBDP results from both Ca and P deficiencies, especially in VLBW infants with comorbidities. P supplementation without treating underlying calcipenia can precipitate hypocalcemia and worsen osteopenia with disastrous consequences. In severe calcipenia, active vitamin D might have a role in addition to an appropriate dose of elemental calcium.

The Role of Nutrition in the Prevention and Management of Bronchopulmonary Dysplasia: A Literature Review and Clinical Approach

Bronchopulmonary dysplasia (BPD) remains the most common severe complication of preterm birth, and nutrition plays a crucial role in lung growth and repair. A practical nutritional approach for infants at risk of BPD or with established BPD is provided based on a comprehensive literature review. Ideally, infants with BPD should receive a fluid intake of not more than 135-150 mL/kg/day and an energy intake of 120-150 kcal/kg/day. Providing high energy in low volume remains a challenge and is the main cause of growth restriction in these infants. They need a nutritional strategy that encompasses early aggressive parenteral nutrition and the initiation of concentrated feedings of energy and nutrients. The order of priority is fortified mother's own milk, followed by fortified donor milk and preterm enriched formulas. Functional nutrient supplements with a potential protective role against BPD are revisited, despite the limited evidence of their efficacy. Specialized nutritional strategies may be necessary to overcome difficulties common in BPD infants, such as gastroesophageal reflux and poorly coordinated feeding. Planning nutrition support after discharge requires a multidisciplinary approach to deal with multiple potential problems. Regular monitoring based on anthropometry and biochemical markers is needed to guide the nutritional intervention.

Metabolic bone disease of prematurity-National survey of current neonatal and paediatric endocrine approaches

AIM

This study aimed to identify current trends in the management of metabolic bone disease of prematurity (MBDP) in the United Kingdom.

METHODS

A nationwide electronic survey was disseminated to all neonatal networks across the United Kingdom, as well as to paediatric endocrinologists for comparison. Weighted averages were used to compare relative importance placed on screening and diagnostic investigations (1 = not important, 5 = essential).

RESULTS

Sixty-nine individuals responded from 53 neonatal units. Greatest emphasis was placed on levels of serum phosphate and alkaline phosphatase for screening (weighted average 4.5 and 4.6, respectively), diagnosis (weighted average 4.1 and 4.5, respectively) and monitoring (93% and 97% of neonatal responders, respectively) of MBDP by neonatologists. Although similar results were obtained for endocrinologists, significantly greater emphasis was placed on plasma parathyroid hormone (PTH) level for screening, diagnosis and monitoring (p < 0.001 for each). Phosphate supplementation was reported almost universally by neonatal responders (99%), but was significantly less for endocrine responders (62%) for the treatment of MBDP (p < 0.001).

CONCLUSION

There is an under-utilisation of plasma PTH as a screening, diagnostic and monitoring investigation to guide appropriate supplementation for MBDP by neonatologists.

Screening of Serum Alkaline Phosphatase and Phosphate Helps Early Detection of Metabolic Bone Disease in Extremely Low Birth Weight Infants

Background: Extremely low birth weight (ELBW, <1,000 g) infants have a high risk of metabolic bone disease (MBD). Because of the late appearance of radiological signs, diagnosis of MBD in ELBW infants might be delayed, and its prevalence underestimated in this group of patients. This study adopted serial screening of serum alkaline phosphatase (ALP) and phosphate (P) of ELBW infants to determine whether such screening is helpful for the early detection of MBD. Materials and Methods: We performed a retrospective study of preterm infants with a gestational age ≤ 31 weeks and birth weight <1,000 g. MBD was absent (ALP ≤500 IU/L), mild (ALP >500 IU/L, P ≥4.5 mg/dL), and severe (ALP >500 IU/L, P <4.5 mg/dL); MBD was divided into early MBD (≤4 weeks after birth) and late MBD (>4 weeks after birth) according to the time of onset. Results: A total of 142 ELBW infants were included, with a median gestational age of 28.1 (26.5-29.7) weeks and a median birth weight of 875 (818-950) g. Seventy-three cases of MBD were diagnosed, and the total prevalence was 51.4% (mild MBD, 10.6%; and severe MBD, 40.8%). Male sex, breastfeeding, and sepsis would increase the risk of severe MBD. Most MBD in ELBW infants occurred at 3-4 weeks after birth. Sixty-two percent (45/73) of infants were diagnosed as having early MBD, which are diagnosed earlier than late MBD [24 (21-26) vs. 39 (36-41), t = -7.161; P < 0.001]. Male sex [odds ratio (OR), 2.86; 95% confidence interval (CI), 1.07-7.64; P = 0.036], initial high ALP levels (OR, 1.02; 95% CI, 1.01-1.03; P < 0.001), and breastfeeding (OR, 5.97; 95% CI, 1.01-25.12; P = 0.049) are independent risk factors for the development of early MBD. Conclusion: The risk of MBD among ELBW infants is very high. Most cases occurred early and were severe. Male sex, initial high ALP levels, and breastfeeding are closely related to the increased risk of early MBD. Serial screening of serum ALP and P helps early detection of MBD; it is recommended to start biochemical screening for ELBW infants 2 weeks after birth and monitor their biochemical markers weekly.

Metabolic Bone Disease of Prematurity: Risk Factors and Associated Short-Term Outcomes

Despite the importance of early recognition of metabolic bone disease (MBD) of prematurity, there is still significant variability in screening practices across institutions. We conducted an observational study of infants born at ≤32 weeks of gestation with a birth weight of ≤1500 g (n = 218) to identify clinical factors associated with biochemical indicators of MBD. Bone mineral status was assessed by measuring alkaline phosphatase and phosphate levels between weeks 3 and 5 of life. Two comparisons were performed after classifying infants as either MBD (cases) or non-MBD (controls), and as either high or low risk for MBD, as determined based on the results of MBD screening. In total, 27 infants (12.3%) were classified as cases and 96 (44%) as high-risk. Compared with controls, MBD infants had a significantly lower gestational age and birth weight, and a longer duration of parenteral nutrition and hospital stay. Respiratory outcomes were significantly poorer in high- versus low-risk infants. Multivariate logistic regression showed that birth weight was the only independent risk factor for MBD (odds ratio [OR]/100 g, 0.811; confidence interval [CI95%], 0.656-0.992; p = 0.045) and that birth weight (OR/100 g, 0.853; CI95%, 0.731-0.991; p = 0.039) and red blood cell transfusion (OR, 2.661; CI95%, 1.308-5.467; p = 0.007) were independent risk factors for high risk of MBD. Our findings provide evidence of risk factors for MBD that could help clinicians to individualize perinatal management. The association of red blood cell transfusion with MBD is a novel finding that may be related to iron overload and that merits further study.

Metabolic bone disease of prematurity: causes, recognition, prevention, treatment and long-term consequences

Metabolic bone disease of prematurity (MBDP) is characterised by skeletal demineralisation, and in severe cases it can result in fragility fractures of long bones and ribs during routine handling. MBDP arises from prenatal and postnatal factors. Infants who are born preterm are deprived of fetal mineral accumulation, 80% of which occurs in the third trimester. Postnatally, it is difficult to maintain a comparable intake of minerals, and medications, such as corticosteroids and diuretic therapy, lead to bone resorption. With improvements in neonatal care and nutrition, the incidence of MBDP in preterm infants appears to have decreased, although the recent practice of administering phosphate supplements alone will result in secondary hyperparathyroidism and associated bone loss, worsening MBDP. Postnatal immobilisation and loss of placental supply of oestrogen also contribute to skeletal demineralisation. There is no single diagnostic or screening test for MBDP, with pitfalls existing for most radiological and biochemical investigations. By reviewing the pathophysiology of calcium and phosphate homeostasis, one can establish that plasma parathyroid hormone is important in determining the aetiology of MBDP - primarily calcipaenia or phosphopaenia. This will then direct treatment with the appropriate supplements while considering optimal physiological calcium to phosphate ratios.

Nutritional Assessment in Preterm Infants: A Practical Approach in the NICU

A practical approach for nutritional assessment in preterm infants under intensive care, based on anthropometric measurements and commonly used biochemical markers, is suggested. The choice of anthropometric charts depends on the purpose: Fenton 2013 charts to assess intrauterine growth, an online growth calculator to monitor intra-hospital weight gain, and Intergrowth-21st standards to monitor growth after discharge. Body weight, though largely used, does not inform on body compartment sizes. Mid-upper arm circumference estimates body adiposity and is easy to measure. Body length reflects skeletal growth and fat-free mass, provided it is accurately measured. Head circumference indicates brain growth. Skinfolds estimate reasonably body fat. Weight-to-length ratio, body mass index, and ponderal index can assess body proportionality at birth. These and other derived indices, such as the mid-upper arm circumference to head circumference ratio, could be proxies of body composition but need validation. Low blood urea nitrogen may indicate insufficient protein intake. Prealbumin and retinol binding protein are good markers of current protein status, but they may be affected by non-nutritional factors. The combination of a high serum alkaline phosphatase level and a low serum phosphate level is the best biochemical marker for the early detection of metabolic bone disease.

Feasibility of quantitative ultrasonography for the detection of metabolic bone disease in preterm infants - systematic review

Metabolic bone disease of prematurity is characterised by disordered bone mineralisation and is therefore an increased fracture risk. Preterm infants are especially at risk due to incomplete in utero bone accretion during the last trimester. Currently, diagnosing metabolic bone disease mainly relies on biochemistry and radiographs. Dual-energy x-ray absorptiometry and quantitative ultrasound (US) are used less frequently. However, biochemical measurements correlate poorly with bone mineralisation and although scoring systems exist for metabolic bone disease, radiographs are subjective and do not detect early features of osteopenia. Dual energy x-ray absorptiometry is the reference standard for determining bone density in older children and adults. However, challenges with this method include movement artefact, difficulty scanning small and sick infants and a lack of normative data for young children. Quantitative US has a relatively low cost, is radiation-free and portable, and may hence be suitable for assessing bone status in preterm infants. This review aims to provide an overview of the use of quantitative US in detecting metabolic bone disease in preterm infants.

Growth and neurodevelopment in very preterm infants receiving a high enteral volume-feeding regimen - a population-based cohort study

AIM

The aim of this study is to evaluate a feeding regimen routinely providing >180 ml/kg/d fortified human milk to very preterm infants and impact on in-hospital growth, osteopenia, and neurodevelopment.

METHOD

Retrospective population-based descriptive study of infants <30-week gestation admitted within 24 h of birth and discharged during the 6-year period 2005-2010. Growth and neurodevelopment was assessed until 2 years corrected age, and cerebral palsy up to 4 years corrected age Results: Ninety-nine infants below 30-week gestation were admitted within 24 h of birth during the 6-year period, of which 84 (85%) survived to discharge. Two infants had surgical necrotizing enterocolitis, both survived to 2 years follow up. Seventy-eight infants (mean 27 weeks) had complete growth data until discharge. Full enteral feeds were tolerated after mean 10 d. Average milk volumes were 193 ml/kg/d from 15 to 42 d of life. Rates of weight below 10th centile were 10% at birth and 14% at discharge. Head circumference Z-scores were stable from birth to discharge. Blood values did not indicate osteopenia. Increasing head circumference Z-scores were associated with improved language development.

CONCLUSIONS

This high enteral feeding volume regimen was associated with low rates of in-hospital growth restriction and good head growth. High enteral volume intake seems safe and may improve nutritional status of very preterm infants.

Changes in Biochemical Parameters of the Calcium-Phosphorus Homeostasis in Relation to Nutritional Intake in Very-Low-Birth-Weight Infants

Preterm infants are at significant risk to develop reduced bone mineralization based on inadequate supply of calcium and phosphorus (Ca-P). Biochemical parameters can be used to evaluate the nutritional intake. The direct effect of nutritional intake on changes in biochemical parameters has not been studied. Our objective was to evaluate the effect of Ca-P supplementation on biochemical markers as serum (s)/urinary (u) Ca and P; alkaline phosphatase (ALP); tubular reabsorption of P (TrP); and urinary ratios for Ca/creatinin (creat) and P/creatinin in Very-Low-Birth-Weight infants on Postnatal Days 1, 3, 5, 7, 10, and 14. This observational study compared two groups with High (n = 30) and Low (n = 40) intake of Ca-P. Birth weight: median (IRQ) 948 (772–1225) vs. 939 (776–1163) grams; and gestational age: 28.2 (26.5–29.6) vs. 27.8 (26.1–29.4) weeks. Daily median concentrations of biochemical parameter were not different between the groups but linear regression mixed model analyses showed that Ca intake increased the uCa and TrP (p = 0.04) and decreased ALP (p = 0.00). Phosphorus intake increased sP, uP and uP/creat ratio and ALP (p ≤ 0.02) and caused decrease in TrP (p = 0.00). Protein intake decreased sP (p = 0.000), while low gestational age and male gender increased renal excretion of P (p < 0.03). Standardized repeated measurements showed that biochemical parameters were affected by nutritional intake, gestational age and gender.

The Clinical and Biochemical Predictors of Bone Mass in Preterm Infants

BACKGROUND

Metabolic bone disease of prematurity still occurs in preterm infants, although a significant improvement in neonatal care has been observed in recent decades. Dual-energy X-ray absorptiometry (DXA) is the precise technique for assessing bone mineral content (BMC) in preterm infants, but is not widely available.

AIM

To investigate the clinical and biochemical parameters, including bone metabolism markers as potential predictors of BMC, in preterm infants up to 3 months corrected age (CA).

MATERIALS AND METHODS

Ca-P homeostasis, iPTH, 25-hydroxyvitamin D, osteocalcin, N-terminal propeptide, cross-linked C-telopeptide and amino-terminal pro C-type natriuretic peptide and the DXA scans were prospectively performed in 184 preterm infants (≤ 34 weeks' gestation) between term age and 3 mo CA. Lower bone mass was defined as BMC below or equal to respective median value for the whole study group, rounded to the nearest whole number.

RESULTS

The appropriate quality DXA scans were available for 160 infants (87%) examined at term and for 130 (71%) tested at 3 mo CA. Higher iPTH level was the only independent predictor of lower BMC at term, whereas lower BMC at 3 mo CA was associated both with lower urinary phosphate excretion and higher serum osteocalcin level. ROC analysis showed that iPTH >43.6 pg/mL provided 40% sensitivity and 88% specificity in identification of preterm infants with lower BMC at term. In turn, urinary phosphate excretion (TRP>97% or UP/Cr ≤0.74 mg/mg) and serum osteocalcin >172 ng/mL provided 40% sensitivity and 93% specificity in identification of infants with decreased BMC at 3 mo CA.

CONCLUSION

Serum iPTH might to be a simple predictor of reduced BMC in preterm infants at term age, but urinary phosphate excretion and serum osteocalcin might predict reduced BMC at 3 mo CA. These results represent a promising diagnostic tool based on simple, widely available biochemical measurements for bone mass assessment in preterm infants.

Screening for secondary hyperparathyroidism in preterm infants

BACKGROUND

The major cause of osteopathy of prematurity is dietary phosphate deficiency, but secondary hyperparathyroidism caused by calcium deficiency or vitamin D deficiency is also important. Because parathyroid hormone (PTH) mobilizes calcium and phosphate from the bone, hyperparathyroidism worsens osteopathy of prematurity. In order to identify useful markers to screen for and diagnose hyperparathyroidism in preterm infants, we measured serum and urinary biochemical markers.

METHODS

Several biomarkers, including serum intact PTH (iPTH), were measured in urine and serum samples obtained from 95 preterm infants, and the relationship between serum iPTH and the other parameters was analyzed.

RESULTS

Mean gestation was 33.2 ± 2.9 weeks, and mean birthweight was 1705 ± 402 g. Samples were collected around postnatal day 17.3 ± 7.4. Fourteen infants (14.7%) had iPTH >65 pg/mL. Cut-offs for serum alkaline phosphatase (ALP) and percent tubular reabsorption rate of phosphate (%TRP) were fixed at 1300 IU/L and 93%, respectively using receiver operating characteristic curves with iPTH cut-off of 65 pg/mL. Serum ALP was proven to be a good marker: ALP had a sensitivity of 78.6% and a specificity of 86.4%, while %TRP itself was not: %TRP had a sensitivity of 64.3% and a specificity of 58.0%. Combined measurement of serum ALP (>1300 IU/L) and %TRP (≤93%), however, had a specificity of 93.8% for detecting elevated iPTH.

CONCLUSION

Measurement of serum ALP (>1300 IU/L) is considered as an effective screening method to detect hyperparathyroidism. In addition, combined assessment of ALP(>1300 IU/L) and %TRP(≤93%) is a good indicator of elevated iPTH in preterm infants.

Bone status in preterm infant: influences of different nutritional regimens and possible markers of bone disease

OBJECTIVE

The objective of this study was to evaluate possible influences of parenteral nutrition on growth and bone development in preterms and to search for markers of bone status.

STUDY DESIGN

Metacarpus bone transmission time (mc-BTT) was performed at birth, 21 days and 36 weeks of gestational age (GA) in preterms, receiving two different nutritional regimens, together with biochemical analysis.

RESULT

A total of 234 patients were studied. Newborns with aggressive nutrition had significantly better growth rate and higher values of mc-BTT until discharge. Mc-BTT at day 21 correlates positively with nutritional intakes and phosphatemia; lower limb length positively correlated with mc-BTT (P<0.01). Newborns with low energy intake in the first week of life (<70 kcal kg(-1) per day) and low serum phosphate level (<1.4 mmol l(-1)) at 21 days had lower mc-BTT at 36 weeks of GA (P<0.01).

CONCLUSION

Aggressive parenteral intakes in preterms improve growth and bone status in the short-medium term, suggesting that early nutrition could influence bone development.

Mineral status of premature infants in early life and linear growth at age 3

BACKGROUND

Preterm infants are at significant risk of reduced bone mineral content and subsequent bone disease (metabolic bone disease of prematurity, MBDP). MBDP is frequently found in very low-birthweight (VLBW) infants, but long-term height prognosis is not well known.

METHODS

VLBW infants from two major neonatal intensive care units were studied. Medical records were reviewed. A total of 143 subjects were analyzed after excluding subjects who died, or who had severe complications that could affect linear growth, Silver-Russell syndrome, severe cholestasis, and/or chromosomal abnormality. The relationship between MBDP and height at age 3 was investigated.

RESULTS

Height standard deviation score (SDS) at age 3 negatively correlated with peak serum alkaline phosphatase (ALP) activity in early life (r = -0.30, P = 0.0003) and positively correlated with serum phosphorus (P) at peak ALP (r = 0.33, P = 0.0002). In addition, serum P independently affected height SDS at 3 years of age (β = 0.19, P = 0.018), and was significantly different between infants with and without catch-up growth in height (difference: 0.23 mmol/L, 95%CI: 0.09-0.36, P = 0.0010).

CONCLUSIONS

MBDP, particularly hypophosphatemia in the early period of life, is associated with linear growth until 3 years of age in VLBW infants.

Prevention of postnatal growth restriction by the implementation of an evidence-based premature infant feeding bundle

OBJECTIVE

To develop an evidence-based feeding bundle to safely decrease the rate of PNGR in VLBW infants.

STUDY DESIGN

The bundle was developed and implemented in January 2010, followed by 3 years of monitoring bundle compliance and infant outcomes (days to first feed (FD), days to reach full feeds (FF), and birth-discharge growth trajectories (delta z-score)).

RESULTS

Data were collected on 482 infants (119 pre-bundle). PNGR decreased from 35% to 19% (P<0.01) and weight delta z-score improved from -0.82 to -0.45 (P<0.001). Percentage of infants with head circumference (HC) below 10th percentile at discharge decreased from 21% to 9% (P<0.01) and HC delta z-score improved from -0.65 to -0.17 (P<0.001). FD and FF also decreased significantly. Rates of necrotizing enterocolitis, peak alkaline phosphatase and peak direct bilirubin levels all trended downward.

CONCLUSIONS

An evidence-based, standardized feeding bundle was safe and effective in reducing the rate of PNGR and in improving head growth in VLBW infants.

Evaluation of bone metabolism in newborn twins using quantitative ultrasound and biochemical parameters

Metabolic bone disease (MBD) is one of the important complications of prematurity. Early and adequate nutritional interventions may reduce the incidence and potential complications of MBD. The present study aimed to evaluate bone metabolism in twins via biochemical parameters and quantitative ultrasound (QUS) and to compare the results between twin pairs. Moreover, twin infants were evaluated in terms of potential risk factors likely to have impact on MBD. Forty-three pairs of twins were included in the study. Serum calcium, phosphorus, magnesium, and alkaline phosphatase concentrations were assessed and bone mineral density was measured using QUS (speed of sound, SOS) at postnatal 30 d. Co-twin with the higher birth weight was assigned to Group 1 (n = 36) and the other twin was assigned to Group 2 (n = 36). Birth weight and head circumference were significantly higher in the infants of Group 1 compared with Group 2. No significant difference was found among the groups in terms of gender, history of resuscitation, length of stay in intensive care unit (ICU) or in the incubator, duration of total parenteral nutrition (TPN), type of nutrition, vitamin D use, biochemical parameters, and the SOS value. The factors likely to affect SOS, including type of pregnancy, maternal drug use, gender of infant, birth weight, head circumference at birth, gestational week, length of stay at the ICU, duration of TPN, type of nutrition, resuscitation, vitamin D use, and levels of calcium, phosphorus, magnesium, and alkaline phosphatase were entered into the model. The phosphorus level and the maternal drug use were found to be the factors that significantly reduced SOS, whereas pregnancy after assisted reproductive techniques was found to be a significant enhancing factor.

Parathyroid hormone as a marker for metabolic bone disease of prematurity

OBJECTIVE

To compare parathyroid hormone to alkaline phosphatase as a serologic marker for metabolic bone disease (MBD) in preterm infants.

STUDY DESIGN

An 18-month prospective observational study in neonates with birth weight < 1250 g. Simultaneous serum parathyroid hormone (PTH), alkaline phosphatase (ALP), calcium (Ca) and phosphorus (P) were measured at scheduled intervals during hospitalization. At 6 weeks of age, MBD was evaluated using knee radiographs. Comparisons were analyzed using multivariate logistic regression, receiver operating characteristic (ROC) curves, χ² and Student t-test.

RESULT

Fourty-nine infants were included in the study: 7 with severe and 42 with mild MBD. Using ROC curves, at 660 U l⁻¹ ALP had a sensitivity of 29% and specificity of 93% for severe MBD, while a cutoff point of 180 pg ml⁻¹ gave PTH a sensitivity of 71% and specificity of 88%. Infants with severe bone disease had a lower birth weight, 21-day serum P, an increased use of glucocorticoids and caffeine, and more likely to have major neonatal morbidities.

CONCLUSION

PTH is an early marker with better sensitivity than ALP in screening for MBD. At 3 weeks chronologic age, a PTH level > 180 mg dl⁻¹ or a P level <4.6 pg ml⁻¹ yielded a sensitivity of 100% and specificity of 94% for severe MBD [corrected].

Metabolic bone disease and bone mineral density in very preterm infants

OBJECTIVES

To evaluate bone mineral density (BMD) in preterm neonates at discharge and identify the optimum cutoff values for serum alkaline phosphatase (ALP) and phosphorus (P) concentrations to diagnose the severity of metabolic bone disease of prematurity.

STUDY DESIGN

A total of 336 preterm neonates (≤ 31 weeks' gestation and birth weight ≤ 1500 g) were prospectively evaluated for BMD before discharge using dual-energy X-ray absorptiometry.

RESULTS

BMD reference values (at ALP ≤ 500 IU/L) were measured in 279 patients. BMD was classified as poor (<10th percentile) at <0.068 g/cm(2), fair (10th-25th percentile) at 0.068-0.081 g/cm(2), good (25th-75th percentile) at 0.081-0.112 g/cm(2), and very good (>75th percentile) at >0.112 g/cm(2). Increased BMD was associated with a higher birth weight, short duration of parenteral nutrition, and the absence of small for gestational age status, patent ductus arteriosus, intraventricular hemorrhage, and other clinical variables. Metabolic bone disease of prematurity was absent (ALP ≤ 500 IU/L) in 279 cases (83.0%), mild (ALP >500 IU/L and P ≥ 4.5 mg/dL) in 46 cases (13.7%), and severe (ALP >500 IU/L and P <4.5 mg/dL) in 11 cases (3.3%).

CONCLUSIONS

A BMD >0.068 g/cm(2) at discharge indicated a 90.3% probability of not developing metabolic bone disease of prematurity. The factors independently associated with increased BMD included higher birth weight, short duration of parenteral nutrition, absence of intraventricular hemorrhage, exclusive feeding of fortified breast milk, and older age at discharge.

Assessment of bone health in preterm infants through quantitative ultrasound and biochemical markers

OBJECTIVE

To assess bone status in preterm infants with quantitative ultrasound and to search for biochemical markers of bone health.

METHODS

Metacarpus bone transmission time (mcBTT) was prospectively performed during hospitalization, together with biochemical and clinical outcomes analysis.

RESULTS

154 patients were studied. At 3rd week of life mcBTT positively correlated with serum phosphate. Urinary excretion of calcium and phosphate were assessed in a subgroup of 55 patients: on day 21 mcBTT positively correlated with phosphaturia, negatively with calciuria. Gestational age (GA), weight and length at 3rd week and at 36 weeks of GA correlated positively with mcBTT. We found negative correlation between mcBTT at 3rd week and days of parenteral nutrition, mechanical ventilation period and days to reach 1800 g.

CONCLUSIONS

Serum phosphate, phosphaturia and calciuria correlate most with mcBTT. Further studies are necessary to verify the possible influence of early bone status on future bone health.

[Neonatal parenteral nutrition prescription practices in Portugal]

INTRODUCTION

The use of guidelines for neonatal parenteral nutrition (PN) improves its clinical efficiency and the safety of prescription.

OBJECTIVE

To evaluate the practices of neonatal parenteral nutrition prescription in Portugal, and the adherence to the National Consensus on neonatal PN (2008).

METHODS

A questionnaire based on a multiple choice response on parenteral nutrition prescription was conducted, and sent to the coordinators of the 50 public and private Portuguese neonatal special care units, 25 being level III and 25 level II.

RESULTS

Parenteral nutrition was prescribed in 32 neonatal units, 23 of which (71.9%) responded to the questionnaire. Of the respondents, 19 (82.6%) refer to follow the National Consensus, the remaining following local guidelines; 17 (73.9%) of units referred to using an electronic based system for prescription. In preterm neonates, most mentioned: administering judiciously the fluid intake during the first post-natal week; starting amino acids from the first post-natal day with 1.5-3g/kg/d, increasing up to 3-4g/kg/d; starting lipids from the first three post-natal days with 1g/kg/d, increasing up to 3g/kg/d; administering 40-70mg/kg/d of calcium and of phosphorus with the fixed calcium:phosphorus ratio of 1.7: 1 (mg:mg); and estimating the osmolality of the solutions, and weekly monitoring of serum triglycerides, blood urea, serum phosphorus and liver function.

CONCLUSIONS

The high response rate is probably representative of the practice of PN prescription in Portugal. Most of the units used the National Consensus on neonatal PN as a reference, thus contributing to better nutritional support for neonates.