Joel D Smith1, Scott Wilson2,3, Hans G Schneider4,3. 1. Clinical Biochemistry Unit, Alfred Pathology Service, Alfred Health, Melbourne, Australia. 2. Department of Renal Medicine, Alfred Health, Melbourne, Australia. 3. Monash University, Melbourne, Victoria, Australia. 4. Clinical Biochemistry Unit, Alfred Pathology Service, Alfred Health, Melbourne, Australia; schneiderh@alfred.org.au.
Abstract
BACKGROUND: Clinical laboratories measure total calcium and adjust for albumin concentrations to predict calcium status. We compared total and adjusted calcium (Adj-Ca) with ionized calcium (Ca2+) for correct assignment of calcium status. The effect of restriction of Adj-Ca reporting in patients with hypoalbuminemia was determined on the basis of frequency of misclassifications. METHODS: Extraction of laboratory results was performed for 24 months. Adj-Ca was calculated from a modified Payne formula. A further prospective data set for 6 months was collected after stopping reporting of Adj-Ca for patients with an albumin <3.0 g/dL. The agreement between Ca2+ and Adj-Ca or total Ca was assessed with Cohen's kappa statistic. RESULTS: In 5553 hospitalized patients, 13604 paired Ca2+ results were analyzed retrospectively. Prospective collection in 1113 paired samples was from 450 patients. Adj-Ca was a poor predictor of calcium status compared to the Ca2+ reference standard in both data sets (agreement 56.9% in the first, 65.6% in the second data set). Renal failure and low albumin concentrations were associated with worse agreement between Adj-Ca and Ca2+. Restriction of reporting of Adj-Ca to albumin concentrations >3.0g/dL improved correct classification of calcium status from 65.6% to 77.6% (P < 0.0001). Total Ca performed better than Adj-Ca for low albumin (<3.0g/dL) and performed similarly in samples with albumin >3.0g/dL. CONCLUSIONS: Adj-Ca is unreliable for the classification of calcium status in hospital patients when compared to Ca2+. Adj-Ca overestimates calcium for patients with renal impairment and albumin concentrations <3.0g/dL. Restriction of reporting Adj-Ca for albumin below 3.0 g/dL reduces the number of misclassified patients.
BACKGROUND: Clinical laboratories measure total calcium and adjust for albumin concentrations to predict calcium status. We compared total and adjusted calcium (Adj-Ca) with ionizedcalcium (Ca2+) for correct assignment of calcium status. The effect of restriction of Adj-Ca reporting in patients with hypoalbuminemia was determined on the basis of frequency of misclassifications. METHODS: Extraction of laboratory results was performed for 24 months. Adj-Ca was calculated from a modified Payne formula. A further prospective data set for 6 months was collected after stopping reporting of Adj-Ca for patients with an albumin <3.0 g/dL. The agreement between Ca2+ and Adj-Ca or total Ca was assessed with Cohen's kappa statistic. RESULTS: In 5553 hospitalized patients, 13604 paired Ca2+ results were analyzed retrospectively. Prospective collection in 1113 paired samples was from 450 patients. Adj-Ca was a poor predictor of calcium status compared to the Ca2+ reference standard in both data sets (agreement 56.9% in the first, 65.6% in the second data set). Renal failure and low albumin concentrations were associated with worse agreement between Adj-Ca and Ca2+. Restriction of reporting of Adj-Ca to albumin concentrations >3.0g/dL improved correct classification of calcium status from 65.6% to 77.6% (P < 0.0001). Total Ca performed better than Adj-Ca for low albumin (<3.0g/dL) and performed similarly in samples with albumin >3.0g/dL. CONCLUSIONS:Adj-Ca is unreliable for the classification of calcium status in hospital patients when compared to Ca2+. Adj-Ca overestimates calcium for patients with renal impairment and albumin concentrations <3.0g/dL. Restriction of reporting Adj-Ca for albumin below 3.0 g/dL reduces the number of misclassified patients.
Authors: Juan C Ramirez-Sandoval; Pablo Diener-Cabieses; Fabián Gutiérrez-Valle; Sofía Ley-Tapia; Santiago Pastrana-Brandes; Pablo E Galindo; Reynerio Fagundo; Mauricio Moreno-Yañez; Alfredo Adolfo Reza-Albarrán; Ricardo Correa-Rotter Journal: Int Urol Nephrol Date: 2022-03-16 Impact factor: 2.266