Reconsideration of Albumin corrected total calcium Determinations: Potential errors in the Clinical management of disorders of calcium metabolism

Background: The formula, referenced in major textbooks, for albumin corrected calcium [Calcium(alb)] may not accurately depict ionized calcium [ICa]. We evaluated the accuracy of unadjusted calcium [Calcium(Unadjusted)] and [Calcium(alb)], and developed a protocol for local laboratory adjustment of calcium for albumin.Methods: Laboratory data were obtained from an electronic health record. Assessments were accuracy, false positive, and false negative rates. Clinical reliability was defined in error zones for calcium [Ca]: Zone A = Ca (normal), ICa(low); Zone B = Ca(low), ICa(normal); and Zone C = Ca(normal), ICa(high), Zone D = Ca(high), ICa (normal).Results: A linear regression from 468 laboratory tests was used to derive a formula for revised corrected calcium [Calcium (revised)] over a range of albumin concentrations where, [Calcium (revised)] = plasma calcium (mg/dl) + [(4-Albumin (g/d)L)]*(plasma calcium (mg/dl)*0.052)]. [Calcium(alb]] vs [Calcium(Unadjusted)] decreased zone B errors 12%, [95%CI;8-15%], vs 44% [95%CI;37-50%], p < 0.001. However, [Calcium(alb]] vs [Calcium(U-nadjusted)] increased zone A error (60%,[95%CI;42-78%], vs 7% [95%CI;1-13%], p < 0.001). [Calcium (revised)] decreased zone A errors (15%, [95%CI;6-24%]) vs [Calcium(alb) ] (60% [95%CI;42-78%], p < 0.001) and Zone D errors from 9% [95%CI;6-12%] to 2% [95%CI;1:5%, p < 0.001].Conclusions: [Calcium(alb)] is unreliable in hypo-or hypercalcemia. We provide a protocol for locally derived correction of calcium for albumin.

Automated summary

In this study, the accuracy of unadjusted calcium and albumin corrected calcium was evaluated. It was found that albumin corrected calcium is unreliable in hypo- or hypercalcemia. A new algorithm for adjusting calcium based on albumin levels was proposed.