Which chemical prevents clotting in a blood specimen and is commonly used in chemistry tests?

Which chemical prevents clotting in a blood specimen and is commonly used in chemistry tests?

• A. EDTA
• B. Citrate
• C. Sodium fluoride
• D. Heparin

Answer: (D)

The key idea is choosing an anticoagulant that keeps the sample liquid without interfering with the chemistry tests. Heparin prevents clotting by activating antithrombin III, which neutralizes thrombin and factor Xa, stopping the coagulation cascade. This leaves plasma available for a wide range of chemistry assays and tends to have minimal interference with the tests, making it the preferred anticoagulant for many chemistry panels. In contrast, EDTA works by binding calcium, which is essential for many enzymes and reactions; it is excellent for preserving cells for a complete blood count but can skew chemistry results. Citrate also chelates calcium and is mainly used for coagulation studies; it can dilute the sample and affect other chemistry measurements. Sodium fluoride is not an anticoagulant—it inhibits glycolysis to preserve glucose and is used with oxalate for glucose testing, so it doesn’t prevent clotting on its own.

The key idea is choosing an anticoagulant that keeps the sample liquid without interfering with the chemistry tests. Heparin prevents clotting by activating antithrombin III, which neutralizes thrombin and factor Xa, stopping the coagulation cascade. This leaves plasma available for a wide range of chemistry assays and tends to have minimal interference with the tests, making it the preferred anticoagulant for many chemistry panels.

In contrast, EDTA works by binding calcium, which is essential for many enzymes and reactions; it is excellent for preserving cells for a complete blood count but can skew chemistry results. Citrate also chelates calcium and is mainly used for coagulation studies; it can dilute the sample and affect other chemistry measurements. Sodium fluoride is not an anticoagulant—it inhibits glycolysis to preserve glucose and is used with oxalate for glucose testing, so it doesn’t prevent clotting on its own.