Which of the following statements explains why a light blue top tube must be completely filled when collecting blood for coagulation studies?

Prepare for the CAMLPR Specimen Collection Competency Test. Practice with diverse question sets including multiple-choice and flashcards. Each question includes hints and explanations to help you become proficient before the exam.

The key idea is the need to keep the blood-to-anticoagulant ratio correct for coagulation testing. Light blue tubes contain sodium citrate, an anticoagulant that binds calcium to prevent clotting. Tests like PT and aPTT rely on a precise ratio of blood to citrate (9 parts blood to 1 part citrate). If the tube isn’t filled fully, the amount of citrate relative to the blood changes, which alters the calcium binding and skews clotting times. Underfilled tubes dilute the blood sample with too much citrate, lengthening clotting times; overfilled tubes reduce citrate, shortening them. Either way, results become unreliable, which is why complete filling is essential. Sealing, contamination, or transport expansion aren’t the main factors that determine the accuracy of these coagulation measurements.