What substance is found in the purple tubes used for blood collection?

The correct response is Ethylenediaminetetraacetate (EDTA), which is the additive found in purple-top tubes used for blood collection. EDTA functions as an anticoagulant by binding to calcium ions in the blood, effectively preventing clot formation. This property makes it ideal for various hematology tests, including complete blood counts (CBC), where preserving the integrity of the blood cells is essential for accurate results.

In clinical practice, purple-top tubes are specifically designed to maintain the stability of cellular components and are frequently used in laboratory settings to ensure that the blood samples remain in a non-clotted state. If a sample is clotted, it could lead to inaccurate results, which is why the proper use of EDTA in these tubes is crucial.

The other substances mentioned are not found in purple tubes. Heparin, for instance, is used in green tubes and acts as an anticoagulant by inhibiting thrombin. Sodium citrate, on the other hand, is present in blue-top tubes and also acts as an anticoagulant but through a different mechanism that involves binding calcium as well. Lastly, calcium is not an additive but rather a vital component in the coagulation cascade, and its presence in blood samples could lead to clot