NHA Phlebotomy Certification Practice Exam

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What substance is used as an additive in the blue top tube for PT/PTT testing?

Sodium Citrate
EDTA
Heparin
Potassium Oxalate

The correct answer is: Sodium Citrate

The blue top tube is specifically designed for coagulation studies, including Prothrombin Time (PT) and Partial Thromboplastin Time (PTT) tests. The additive used in the blue top tube is sodium citrate, which functions as an anticoagulant. When blood is collected into this tube, sodium citrate binds calcium ions in the blood sample. By chelating calcium, it effectively prevents the blood from clotting, allowing for accurate measurement of clotting factors during laboratory analysis. This anticoagulation property is crucial, as PT and PTT tests evaluate the time it takes for blood to clot, providing vital information regarding the coagulation cascade and potential bleeding disorders. Using sodium citrate in the blue top tube ensures that the collected sample is suitable for these specific tests without compromising the results.