First tube drawn if you only need a coagulation test?

First tube drawn if you only need a coagulation test?

• A. Red top tube
• B. Lt blue discard tube
• C. Green top tube
• D. Lavender top tube

Answer: (B)

Coagulation testing relies on an uncontaminated blood sample collected in a sodium citrate tube because citrate preserves the clotting factors by binding calcium, and the tube must be filled to the correct 9:1 blood-to-anticoagulant ratio. Drawing and discarding the first tube helps flush away any contaminants from the venipuncture site or IV line (such as tissue thromboplastin or IV fluids) that could skew results. The other tube types introduce substances that alter coagulation measurements: red tops yield serum, not suitable for clotting studies; green tops contain heparin which can affect results; lavender tops contain EDTA which chelates calcium and disrupts coagulation tests.

Coagulation testing relies on an uncontaminated blood sample collected in a sodium citrate tube because citrate preserves the clotting factors by binding calcium, and the tube must be filled to the correct 9:1 blood-to-anticoagulant ratio. Drawing and discarding the first tube helps flush away any contaminants from the venipuncture site or IV line (such as tissue thromboplastin or IV fluids) that could skew results. The other tube types introduce substances that alter coagulation measurements: red tops yield serum, not suitable for clotting studies; green tops contain heparin which can affect results; lavender tops contain EDTA which chelates calcium and disrupts coagulation tests.