Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

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Which blood collection tube is used for WBC counts?

Blue stopper
Grey stopper
Black stopper
Lavender stopper

The correct answer is: Lavender stopper

The lavender stopper blood collection tube is specifically designed for complete blood counts (CBC), which includes white blood cell (WBC) counts. This type of tube contains ethylenediaminetetraacetic acid (EDTA), an anticoagulant that prevents blood from clotting. By using a tube with EDTA, the sample remains in a liquid state, which is essential for accurate cell counting, particularly for WBCs, since any coagulation could lead to inaccurate or misleading results. The other tubes mentioned are used for different purposes: the blue stopper tube is typically used for coagulation studies, the grey stopper tube is primarily used for glucose levels or lactate measurements, and the black stopper is often utilized for specific sedimentation rate tests. Each type of tube contains different additives tailored for specific laboratory tests, making the lavender stopper tube the correct choice for WBC counts.