Which tube is used for coagulation studies such as PT/INR?

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Multiple Choice

Which tube is used for coagulation studies such as PT/INR?

Coagulation testing hinges on using a blood sample that is kept from clotting until the lab is ready to run the test, but can be brought to clot under controlled conditions during the assay. The light-blue top tube contains sodium citrate, an anticoagulant that binds calcium to prevent clotting in the collection tube. This preserves the plasma and the clotting factors so the lab can accurately measure how long it takes for clot formation when calcium and thromboplastin are later added. It’s crucial that the tube is filled to the correct volume (roughly a 9:1 blood-to-citrate ratio); underfilling leaves too much citrate and prolongs PT/INR results, while overfilling can distort them as well. After collection, mix gently to distribute the citrate, then centrifuge to obtain plasma for testing. Other common tubes use different additives (like EDTA or heparin) or collect serum, which interfere with calcium-dependent clotting tests, so they aren’t appropriate for PT/INR. That’s why the light-blue top tube is the correct choice for coagulation studies.

Coagulation testing hinges on using a blood sample that is kept from clotting until the lab is ready to run the test, but can be brought to clot under controlled conditions during the assay. The light-blue top tube contains sodium citrate, an anticoagulant that binds calcium to prevent clotting in the collection tube. This preserves the plasma and the clotting factors so the lab can accurately measure how long it takes for clot formation when calcium and thromboplastin are later added. It’s crucial that the tube is filled to the correct volume (roughly a 9:1 blood-to-citrate ratio); underfilling leaves too much citrate and prolongs PT/INR results, while overfilling can distort them as well. After collection, mix gently to distribute the citrate, then centrifuge to obtain plasma for testing. Other common tubes use different additives (like EDTA or heparin) or collect serum, which interfere with calcium-dependent clotting tests, so they aren’t appropriate for PT/INR. That’s why the light-blue top tube is the correct choice for coagulation studies.

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