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(Unadjusted)] 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.

Novel method for measuring S-nitrosothiols using hydrogen sulfide.

Recent advances in techniques that allow sensitive and specific measurement of S-nitrosothiols (RSNOs) have provided evidence for a role for these compounds in various aspects of nitric oxide (NO) biology. The most widely used approach is to couple reaction chemistry that selectively reduces RSNOs by one electron to produce NO, with the sensitive detection of the latter under anaerobic conditions using ozone based chemiluminescence in NO analyzers. Herein, we report a novel reaction that is readily adaptable for commercial NO analyzers that utilizes hydrogen sulfide (H2S), a gas that can reduce RSNO to NO and, analogous to NO, is produced by endogenous metabolism and has effects on diverse biological functions. We discuss factors that affect H2S based methods for RSNO measurement and discuss the potential of H2S as an experimental tool to measure RSNO.