In routine phlebotomy practice, which colour coded vacutainer tube is typically used for coagulation tests such as prothrombin time (PT) and activated partial thromboplastin time (aPTT)?

Introduction / Context:
Phlebotomy, the practice of drawing blood for laboratory testing, relies on standard colour coded tubes that contain different additives. Correct tube selection is critical because the additive can directly affect the test result. Coagulation tests such as prothrombin time and activated partial thromboplastin time assess the clotting system and therefore require a tube that preserves clotting factors in a very specific way. This question checks whether you know which tube colour and additive are used for such coagulation studies.

Given Data / Assumptions:

• We are concerned with tests like prothrombin time and activated partial thromboplastin time.
• Options list common tube colours and additives used in phlebotomy.
• We assume familiarity with basic laboratory practice or general nursing and medical entrance content.

Concept / Approach:
Coagulation tests require anticoagulated plasma in which clotting factors have not been consumed. The standard tube used is the light blue top vacutainer containing sodium citrate. Sodium citrate binds calcium reversibly, preventing clotting while preserving the clotting factors. In the laboratory, calcium can be added back in a controlled manner to initiate clotting and measure clotting times. Tubes with EDTA, heparin, or no anticoagulant are designed for other types of tests and are not appropriate for routine coagulation profiles.

Step-by-Step Solution:
Step 1: Identify the tests in the question as coagulation studies, which require special handling. Step 2: Recall that light blue top tubes with sodium citrate are standard for coagulation testing because citrate preserves clotting factors by binding calcium. Step 3: Compare this with lavender top tubes containing ethylenediaminetetraacetic acid, which are usually used for complete blood counts and haematology because EDTA strongly chelates calcium and preserves cell morphology. Step 4: Note that green top heparin tubes and red top plain tubes serve other purposes, such as some chemistry tests or serology, and are not the first choice for PT or activated partial thromboplastin time.

Verification / Alternative check:
Standard phlebotomy guides and laboratory manuals provide colour coding charts. In these charts, the light blue top tube with sodium citrate is always listed under coagulation tests such as PT, activated partial thromboplastin time, and D dimer. Nurses and phlebotomists are trained to follow this colour coding so that the correct additive is used for each test. This consistency across institutions confirms the link between light blue tubes and coagulation studies.

Why Other Options Are Wrong:

• Lavender top with ethylenediaminetetraacetic acid: Mainly used for complete blood count and other haematology tests; the strong chelation by ethylenediaminetetraacetic acid is not suited for standard coagulation timing assays.
• Green top with heparin: Used for some chemistry tests and special studies where plasma is required, but heparinised samples are not standard for routine coagulation time measurements.
• Red top plain tube: This tube allows blood to clot and is commonly used for serum based tests, not for measuring clotting times that require plasma with intact clotting factors.

Common Pitfalls:
A frequent source of error is confusing the lavender and light blue tubes because both are commonly used. Remember that lavender top tubes are closely associated with complete blood counts, while light blue top tubes are strongly associated with coagulation tests. Another pitfall is assuming any anticoagulant tube can be used for any test. In reality, each additive has a specific purpose, and using the wrong tube can invalidate results and require repeat blood draws.

Final Answer:
Coagulation tests such as prothrombin time and activated partial thromboplastin time are collected in a light blue top tube containing sodium citrate.