Nephrology (Carlton). 2021 Jun 5. doi: 10.1111/nep.13910. Online ahead of print.
ABSTRACT
BACKGROUND: Albumin-adjusted calcium remains widely used in clinical practice with guidelines for chronic kidney disease (CKD) mineral bone disorder recommending the use of serum calcium for monitoring. This is despite ionised calcium being the biologically active fraction. This study aimed to investigate the ability of total calcium and albumin-adjusted calcium to correctly assign calcium status in stage 5/5D CKD across non-dialysis, haemodialysis and peritoneal dialysis patients.
METHODS: Over a 6-months, 352 paired serum and ionised calcium samples were collected from stage 5 (n = 58) and 5D (n = 294, 196 haemodialysis, 98 peritoneal dialysis) CKD patients in a tertiary-hospital setting. Albumin-adjusted calcium was calculated using the modified-Payne formula. Ionised calcium was the reference standard. The agreement between the two methods in assigning calcium status was assessed using Cohen’s weighted kappa (κ) statistic.
RESULTS: Albumin-adjusted calcium was a poor predictor of calcium status compared to ionised calcium in stage 5/5D CKD (observed agreement 0.42, weighted κ 0.20, 95% CI 0.15-0.26). Dialysis dependence was associated with worse agreement (observed agreement 0.38, weighted κ 0.14, 95% CI 0.09-0.19). Total calcium was more reliable however remained inaccurate. Calcium status was not more accurately classified in those with higher albumin levels ≥30 g/L (observed agreement 0.47, weighted κ 0.23, 95% CI 0.10-0.36).
CONCLUSION: Total calcium provides better approximation of calcium status than albumin-adjusted calcium in stage 5/5D CKD. Albumin-adjusted calcium tends to ‘overcorrect’ serum calcium upward. Clinicians should use ionised calcium where accurate measure of calcium is indicated, with total calcium used as the next best option where resources are limited.
PMID:34089212 | DOI:10.1111/nep.13910