New Predictive Equations for Serum Ionized Calcium in Hospitalized Patients

Understanding the Korean Dialysis Cohort for Mineral, Vascular Calcification, and Fracture (ORCHESTRA) Study: Design, Method, and Baseline Characteristics

INTRODUCTION

End-stage renal disease (ESRD) is a growing disease worldwide, including Korea. This is an important condition that affects patient outcome. To provide optimal management for mineral disturbance, vascular calcification, and bone disease in ESRD patients, the Korean dialysis cohort for mineral, vascular calcification, and fracture (ORCHESTRA) study was conducted by enrolling Korean dialysis patients.

METHODS

Sixteen university-affiliated hospitals and one Veterans' Health Service Medical Center participated in this study. This prospective cohort study enrolled approximately 900 consecutive patients on dialysis between May 2019 and January 2021. Enrolled subjects were evaluated at baseline for demographic information, laboratory tests, radiologic imaging, and bone mineral densitometry (BMD) scans. After enrollment, regular assessments of the patients were performed, and their biospecimens were collected according to the study protocol. The primary outcomes were the occurrence of major adverse cardiovascular events, invasive treatment for peripheral artery disease, and osteoporotic fractures. The secondary outcomes were hospitalization for cerebrovascular disease or progression of abdominal aortic calcification. Participants will be assessed for up to 3 years to determine whether primary or secondary outcomes occur.

RESULTS

Between May 2019 and January 2021, all participating centers recruited 900 consecutive dialysis patients, including 786 undergoing hemodialysis (HD) and 114 undergoing peritoneal dialysis (PD). The mean age of the subjects was 60.4 ± 12.3 years. Males accounted for 57.7% of the total population. The mean dialysis vintage was 6.1 ± 6.0 years. The HD group was significantly older, had a longer dialysis vintage, and more comorbidities. Overall, the severity of vascular calcification was higher and the level of BMD was lower in the HD group than in the PD group.

CONCLUSION

This nationwide, multicenter, prospective cohort study focused on chronic kidney disease-mineral and bone disorder and aimed to provide clinical evidence to establish optimal treatment guidelines for Asian dialysis patients.

Measurement of plasma total calcium before plasma free ionized calcium - a possibility with affordable pitfalls

Free ionized calcium (fCa) is considered the gold standard for assessing calcium status in patients, but it is relatively expensive and is associated with several preanalytical and analytical error sources. We investigated the feasibility of using a reflex test that involves first measuring total calcium (tCa) and if out of reference range, then measure fCa, with expectation of reducing the number of fCa measurements. We used data from 1815 unique patients with concurrent measurement of fCa, tCa and albumin adjusted calcium (aCa). Patients were stratified by albumin level, and the association of fCa to tCa and aCa respectively was assessed with linear regression. The regression analysis showed the best linearity for tCa and aCa at albumin <35 g/L (R2: 0.80-0.90), and the poorest at albumin >40 g/L (R2: tCa 0.58; aCa 0.59). We examined the accuracy of hypo- and hypercalcemia classifications for tCa, aCa and the reflex test. aCa had more misclassifications of hypo- and hypercalcemia than tCa, with respectively 25% and 21%. Implementation of the reflex test would correct any false hypo- or hypercalcemia classified by tCa, leaving only false negative results corresponding to 9% of all tCa measurements. False negative results were on average 0.04 mmol/L above or below the reference range of fCa. Implementation of the reflex test reduces the number of fCa by 68% without major errors diagnosing hyper- or hypocalcemia.

A New Predictive Equation for Estimating Serum Ionized Calcium Levels in Patients on Chronic Hemodialysis

BACKGROUND Circulating calcium mainly carries out its physiologic function in its ionized form (iCa). Clinically, iCa is usually estimated by multiplying the total calcium (TCa) level by 0.5 in the general population, but this method is not accurate when applied to patients on long-term hemodialysis (CHD). Accordingly, this study aimed to develop a predictive function for iCa in patients on CHD by incorporating TCa and other additional variables. MATERIAL AND METHODS This was a retrospective cross-sectional study consisting of 2 cross-sectional datasets: a derivation set including 469 CHD patients in June 2019, and a validation set including 446 CHD patients in September 2019. The derivation set's data were analyzed using the stepwise model selection of machine learning with 10-fold cross-validation to develop a predictive function for iCa. This predictive function was then applied to the validation set's data, and the predictive function's estimated iCa was compared with the actual laboratory iCa by using the paired-samples t test and intraclass correlation coefficient. RESULTS After analyzing the routine laboratory data parameters of patients in the derivation set, the following 5 variables were included in the predictive function of iCa: blood urea nitrogen, creatinine, phosphate, TCa, and albumin. This predictive function was applied to the validation set to yield an estimated iCa level that was not significantly different from the laboratory-measured iCa level of the validation dataset (P=0.676) with an excellent ICC of 0.905. CONCLUSIONS We developed a new predictive function that accurately measures the iCa in patients on CHD by using routine laboratory data.

The Effect of Pre-Thyroidectomy Calcitriol Prophylaxis on Post-Thyroidectomy Hypocalcaemia in Children

INTRODUCTION

Transient or persistent hypoparathyroidism is one of the most well-known complications of total thyroidectomy and may lead to symptomatic hypocalcaemia. In children, treatment of post-thyroidectomy hypocalcaemia usually consists of postoperative calcium and/or vitamin D supplementation. In 2013, we implemented prophylactic pre-thyroidectomy calcitriol supplementation for all children undergoing total thyroidectomy at the Amsterdam UMC. The objective of this study was to evaluate the efficacy of this prophylactic calcitriol supplementation in preventing post-thyroidectomy hypocalcaemia in children.

METHODS

In a retrospective case study, we included all children (age <18 years), who underwent a total or completion thyroidectomy in the Amsterdam UMC, between 2000 and 2020. Patients were divided into two groups, patients with preoperative calcitriol supplementation and those without (controls). Hypocalcaemia was defined as total serum calcium concentration of <2.0 mmol/L. The primary outcome measure was the occurrence of hypocalcaemia in the first 72 h after surgery. Secondary outcome measures were occurrence of symptomatic hypocalcaemia, need for medical intervention within the first 72 h after surgery, and length of hospitalization.

RESULTS

A total of 51 patients were included; 26 with calcitriol prophylaxis and 25 controls. There was no significant difference in occurrence of hypocalcaemia (17/26 prophylaxis group; 18/25 control group). Median postoperative calcium concentrations in the first 72 h were significantly higher in the group with prophylaxis at 30-35 h (2.26 vs. 2.01 mmol/L) and 36-41 h (2.17 vs. 1.92 mmol/L). Occurrence of symptomatic hypocalcaemia, need for medical intervention, and length of hospitalization were not significantly different between the groups.

CONCLUSION

Calcitriol prophylaxis resulted in somewhat higher postoperative calcium concentrations but did not reduce the occurrence of hypocalcaemia or affect clinical outcome measures such as occurrence of symptomatic hypocalcaemia and length of postoperative hospitalization.

Poor performance of albumin or protein-adjusted plasma calcium to diagnose dyscalcemia in hospitalized patients: A confirmatory study in a general internal medicine department

INTRODUCTION

Hypo- and hypercalcemia are common and some causes require urgent diagnosis and treatment. Measurement of ionized calcium is the reference test to diagnose calcium disorders but total calcium adjusted for protein or albumin concentration is more often used.

METHODS

Patients hospitalised in a general internal medicine department from September 2013 to December 2015 who had a total plasma calcium concentration and a serum albumin or protein concentration measured within 24h of a ionized calcium blood measurement were included. Total calcium was adjusted for protein or albumin concentration using widely used formulas and compared to ionized calcium as the gold standard.

RESULTS

Among 210 included patients, 46 (22%) had hypocalcemia, 124 (59%) normocalcemia and 40 (19%) hypercalcemia according to ionized calcium concentration. Total calcium had 50% sensitivity and 95% specificity to diagnose hypocalcemia and a 93% sensitivity and 89% specificity to diagnose hypercalcemia. Adjusting total calcium for protein or albumin concentrations did not increase and sometimes decreased diagnostic accuracy.

CONCLUSION

Total calcium, with or without albumin/protein adjustment, is poorly sensitive to screen for hypocalcemia. Unadjusted total calcium is as sensitive as protein- or albumin-adjusted total calcium to screen for hypercalcemia. These data argue against the use of albumin- or protein-adjusted calcium. Ionized calcium measurement should be performed to confirm dyscalcemia in patients with abnormal total calcium concentration and to rule out hypocalcemia in patients with total calcium concentration in the lower range of normal values.

Serum sodium variation is a major determinant of peridialytic blood pressure trends in haemodialysis outpatients

Intradialytic hypotension (IDH) and peridialytic blood pressure (BP) trends are associated with morbidity and mortality in haemodialysis (HD) patients. We aimed to characterise the respective influence of volume status and small solutes variation on peridialytic systolic BP (SBP) trends during HD. We retrospectively analysed the relative peridialytic SBP decrease in 647 prevalent outpatients attending for their mid-week session with corresponding pre- and post-HD bioelectrical impedance analysis. Mean SBP decreased by 10.5 ± 23.6 mmHg. Factors positively associated with the relative decrease in SBP were: serum sodium (Na) decrease, body mass index, serum albumin, dialysis vintage, ultrafiltration rate and urea Kt/V (p < 0.05 for all). Antihypertensive medications and higher dialysate calcium were negatively associated with the relative decrease in SBP (p < 0.05 for both). Age had a quadratic relationship with SBP trends (p < 0.05). Pre-HD volume status measured by extracellular to total body water ratio was not associated with SBP variation (p = 0.216). Peridialytic SBP trends represent a continuum with serum Na variation being a major determinant while volume status has negligible influence. Middle-aged and overweight patients are particularly prone to SBP decline. Tailoring Na and calcium dialysate concentrations could influence haemodynamic stability during HD and improve patient experience and outcomes.

Comparison of fractional excretion of electrolytes in patients at different stages of chronic kidney disease: A cross-sectional study

Kidney handling of electrolytes varies in different stages of chronic kidney disease (CKD). Diabetes mellitus (DM) plays an important role in CKD. Fractional excretion (FE) is an important means in clinical practice. The relationship between FE of electrolytes in patients at different stages of CKD is worth further investigating.We designed a cross-sectional study in 1 teaching hospital, consecutive CKD patients were enrolled between February 2016 and January 2017. Including clinical demographic features, laboratory examination including spot urine electrolytes, blood biochemistries, and relevant medications were determined.A total of 762 CKD patients completed the study. Of these, 218 (28.6%) had DM. Participants were grouped according to estimated glomerular filtration rate into 7 categories: hyperfiltration (HF), CKD1, CKD2, CKD3a, CKD3b, CKD4, and CKD5. Groups HF, CKD1, 2, 3a, 3b, 4 and 5 contained 83, 143, 192, 94, 82, 82, and 86 patients, respectively. FE of electrolytes tended to increase along with the decline of renal function (CKD1-CKD5) (P < .001). The relationship was similar between the DM and non-DM groups. Diabetic patients demonstrated higher FE of magnesium compared with non-DM subjects at CKD2 and CKD5 (P < .05).CKD patients showed a progressive increase in the FE of electrolytes; FE of magnesium seemed to increase more among diabetic patients with CKD, and could be a potential predictor of CKD progression.

Total and ionized calcium and magnesium are significantly lowered in drug-naïve depressed patients: effects of antidepressants and associations with immune activation

Major depressive disorder (MDD) is associated with alterations in calcium (Ca) and magnesium (Mg), as well as circulating pro- and anti-inflammatory cytokines. Anti-inflammatory drugs are commonly used as adjuvant treatments for MDD. However, no studies examined the effects of a combinatorial treatment with sertraline and ketoprofen, an anti-inflammatory drug, on Ca and Mg levels in MDD. The present study examined a) differences in both cations between drug-naïve MDD patients and controls, and b) the effects of sertraline and ketoprofen on Ca and Mg (both total and ionized). In the same patients, we also examined the associations between both cations and IL-1β, IL-4, IL-6, IL-18, IFN-γ, TGF-β1, zinc, and indoleamine 2,3-dioxygenase (IDO). Clinical improvement was assessed using the Beck Depression Inventory-II (BDI-II) at baseline and after follow up for 2 months. Serum Ca and Mg (total and ionized) were significantly lower in MDD patients as compared with controls, while treatment significantly increased calcium but decreased magnesium levels. There were significant and inverse correlations between the BDI-II scores from baseline to endpoint and Ca (both total and ionized), but not Mg, levels. The effects of calcium on the BDI-II score remained significant after considering the effects of zinc, IDO and an immune activation z unit-weighted composite score based on the sum of all cytokines. There was a significant and inverse association between this immune activation index and calcium levels from baseline to endpoint. In conclusion, lowered levels of both cations play a role in the pathophysiology of major depression. Antidepressant-induced increases in Ca are associated with clinical efficacy and attenuation of the immune response. The suppressant effect of antidepressants on Mg levels is probably a side effect of those drugs. New antidepressant treatments should be developed that increase the levels both Ca and Mg. Graphical abstract.

Effects of pH and the plasma or serum concentrations of total calcium, chloride, magnesium, l-lactate, and albumin on the plasma ionized calcium concentration in calves

Background

The plasma ionized calcium concentration (cCa²⁺) represents the biologically active form of calcium and is the preferred method for evaluating calcium status in animals. Different pH‐corrective equations have been developed for human plasma, but the validity of the equations for bovine plasma is unknown.

Hypothesis

We hypothesized that pH‐corrective equations for bovine plasma would be similar to those used for human plasma; cCa²⁺ was dependent on the plasma concentrations of total calcium (cTCa), chloride (cCl), L‐lactate (cLactate), and albumin (cAlbumin); and the in vitro and in vivo cCa²⁺‐pH relationships would differ.

Animals

Ten healthy calves (in vitro study), 1426 critically ill calves.

Methods

The in vitro plasma log₁₀(cCa²⁺)‐pH relationship was determined by CO₂ tonometry of 465 plasma samples. Plasma cCl was altered by equivolume dilution of plasma with 3 electrolyte solutions of different cCl. The in vivo plasma cCa²⁺‐pH relationship was investigated and validated using clinicopathologic data extracted from the medical records of 950 (model development) and 476 (model validation) critically ill calves.

Results

pH‐corrective equations for bovine plasma were similar to those used for human plasma. Plasma cCa²⁺ increased in vitro with increases in plasma cCl. Plasma cCa²⁺ in critically ill calves was associated with plasma cTCa, blood pH, plasma cCl, serum cMg, and cL‐lactate (R² = 0.69) but not plasma cAlbumin.

Conclusions and Clinical Importance

Calculation of cCa²⁺ from cTCa in calf plasma or serum requires adjustment for at least pH and cCl when 1 or both are outside the reference range.

Ex vivo detection of calcium phosphate and calcium carbonate in rat blood serum

The total calcium (tCa) in blood serum comprises free Ca²⁺ ions (fCa), protein-bound calcium (prCa), and complexed calcium by small anions (cCa). The cCa fraction, in addition to fCa, has been indicated to have some physiological activity. However, there is little evidence for the structure of its constituents. Here we report an ex vivo detection of the cCa constituents by synchrotron X-ray absorption near-edge structure spectroscopy. We collected the data directly on rat blood serum and, by making use of the reference samples, derived a spectrum that exhibits the features of cCa constituents. Among the features are those of the complexes of calcium phosphate and calcium carbonate. The detected complexes in the cCa fraction are mainly Ca(η²-HPO₄)(H₂O)₄ and Ca(η¹-HCO₃)(H₂O)₅⁺, in which HPO₄^2- and HCO₃^- serve as bidentate and unidentate ligands, respectively. The remained H₂O molecules on the coordination sphere of Ca²⁺ enable these complexes to behave partially like aquated Ca²⁺ ions in protein-binding. Besides, as the dominant part of prCa, albumin-bound calcium (albCa) exhibits a spectrum that closely resembles that of fCa, indicating weak interactions between the protein carboxyl groups and calcium. The weak-bound cCa and albCa, along with fCa and the relevant anions, compose a local chemical system that could play a role in maintaining the calcium level in blood.

Comparison of pre-filter and post-filter ionised calcium monitoring in continuous veno-venous hemodiafiltration (CVVHD-F) with citrate anti-coagulation

Background

It is widespread practice during citrate anticoagulated renal replacement therapy to monitor circuit ionised calcium (iCa²⁺) to evaluate the effectiveness of anticoagulation. Whether the optimal site to sample the blood path is before or after the haemofilter is a common question.

Methods

Using a prospectively collected observational dataset from intensive care patients receiving pre-dilution continuous veno-venous haemodiafiltration (CVVHD-F) with integrated citrate anticoagulation we compared paired samples of pre and post filter iCa²⁺ where the target range was 0.3–0.5 mmol.L^-1 as well as concurrently collected arterial iCa²⁺. Two nested mixed methods linear models were fitted to the data describing post vs pre filter iCa²⁺, and the relationship of pre, post and arterial samples.

Setting

An 11 bed general intensive care unit.

Participants

450 grouped samples from 152 time periods in seven patients on CRRT with citrate anticoagulation.

Results

The relationship of post to pre-filter iCa²⁺ was not 1:1 with post = 0.082 + 0.751 x pre-filter iCa²⁺ (95% CI intercept: 0.015–0.152, slope 0.558–0.942). Variation was greatest between patients rather than between circuits within the same patient or citrate dose. Compared to arterial iCa²⁺ there was no significant difference between pre and post-filter sampling sites (F-value 0.047, p = 0.827)

Conclusion

These results demonstrate that there is minimal difference between pre and post filter samples for iCa²⁺ monitoring of circuit anticoagulation in citrate patients relative to the arterial iCa²⁺ in CVVHD-F however compared to pre-filter sampling, post filter sampling has a flatter response and greater variation.