NHA Phlebotomy Certification Practice Exam

Most anticoagulants in blood collection tubes prevent clotting by:

1. Binding calcium.

2. Acting as an antithrombin agent.

3. Binding fibrinogen.

4. Releasing heparin.

The correct answer is: Binding calcium.

The correct answer is that most anticoagulants in blood collection tubes prevent clotting by binding calcium. In the coagulation process, calcium ions play a critical role as they are necessary for many of the steps involved in the formation of a blood clot. By binding calcium, anticoagulants such as EDTA (ethylenediaminetetraacetic acid) and citrate effectively inhibit the clotting cascade, preventing the blood from clotting inside the collection tube. Understanding this mechanism is essential for phlebotomy professionals, as it directly influences the handling and processing of blood samples. When blood is drawn into a tube containing an anticoagulant that binds calcium, it allows for accurate analysis of blood components without the interference of clot formation. This knowledge helps ensure that laboratory results are reliable and reflect the true state of the patient’s blood chemistry. Other anticoagulants work through different mechanisms, but for those commonly used in blood collection, binding calcium is the predominant method.