Abstract：
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.
摘要：
游离离子钙（fCa）被认为是评估患者钙状态的金标准，但它相对昂贵，并与几个分析前和分析误差源有关。我们调查了使用反射测试的可行性，该测试涉及首先测量总钙（tCa），如果超出参考范围，然后测量fCa，期望减少FCa测量的数量。我们使用了1815名独特患者的数据，同时测量了fCa，tCa和白蛋白调节钙(aCa)。患者按白蛋白水平分层，用线性回归法评估fCa分别与tCa和aCa的相关性。回归分析显示，在白蛋白<35g/L时，tCa和aCa的线性最好（R2：0.80-0.90），白蛋白>40g/L时最差(R2:tCa0.58；aCa0.59)。我们检查了tCa的低钙血症和高钙血症分类的准确性，Ca和反射测试。aCa对低钙血症和高钙血症的错误分类比tCa多，分别为25%和21%。反射测试的实施将纠正任何由tCa分类的假低钙血症或高钙血症，只留下假阴性结果，相当于所有tCa测量的9%。假阴性结果平均高于或低于fCa的参考范围0.04mmol/L。反射测试的实施使fCa的数量减少了68％，而没有诊断高血钙或低血钙的重大错误。
