What is the most likely explanation for the low serum calcium results in a red-stoppered tube?

The presence of low serum calcium results in a red-stoppered tube can be attributed to the introduction of anticoagulated blood into the sample. Red-stoppered tubes are typically used for serum collection and do not contain any additives, allowing for clot formation. If anticoagulated blood, such as that from a tube with an additive like EDTA or heparin, is mixed with the serum sample, it can cause a decrease in calcium levels due to the sequestration of calcium ions by the anticoagulant.

Calcium levels in blood are tightly regulated, and the introduction of anticoagulants can bind free calcium ions, leading to artificially low serum calcium measurements. This scenario explains the observed low calcium results, as the anticoagulant interferes with the accurate measurement of calcium in the sample.

In contrast, severe hemolysis during sample collection can cause the release of intracellular components, but it typically does not specifically lower calcium levels; rather, it can affect other analytes. Laboratory error can result from various factors, but once established that the sample collection was done correctly, it's less likely to explain the specific low calcium result. Lastly, if the wrong order of draw was used, it could lead to contamination affecting other tests but would not typically