What could lead to erroneous measurement of calcium if blood is collected in a specific anticoagulant?

The erroneous measurement of calcium in blood samples can be significantly influenced by the choice of anticoagulant used during collection. In this context, oxalate is particularly problematic for calcium measurement because oxalate ions can combine with calcium ions to form insoluble calcium oxalate, thus artificially lowering the levels of calcium that can be detected in the sample.

When blood is collected in a tube containing oxalate, the oxalate binds with free calcium in the plasma, leading to a reduction in the measurable calcium concentration. This reaction distorts the true calcium level present in the sample, leading to misleading results in calcium assays.

In contrast, while heparin, EDTA, and citrate are also anticoagulants used in blood collection and can have effects on calcium measurement, they do so differently. EDTA binds calcium ions, but it is notably more completely dissociative than oxalate, which impacts its usability in calcium assays. Citrate also binds calcium, but, depending on the assay method, it may not cause as significant a disturbance in measured calcium levels when used appropriately. Heparin generally has a lesser impact on calcium levels compared to oxalate and is often used without significant issues in calcium determination.

Thus, when considering