Which anticoagulant is used in the tube for coagulation testing?

AIIMS CRE, SNO-2024

Biochemistry and Nutrition

Easy

Appeared in: AIIMS CRE, SNO-2024

Explanation

Sodium citrate is the anticoagulant of choice for coagulation studies, such as Prothrombin Time (PT) and Activated Partial Thromboplastin Time (aPTT).
It is used in light blue-top collection tubes.
Citrate prevents clotting by binding to calcium ions in the blood, a process that is reversible.
The reversibility is essential because calcium is added back in the lab to start the clotting cascade and measure the time it takes, providing an accurate assessment of the patient's coagulation status.

Option A: EDTA (Ethylenediaminetetraacetic acid) binds calcium too strongly and irreversibly for the purposes of coagulation testing, which would lead to falsely prolonged or unclottable results.
Option B: Heparin prevents clotting by inhibiting key factors in the coagulation cascade, specifically thrombin and Factor Xa. Using it for coagulation tests would directly interfere with the measurement of the cascade's function.
Option D: Oxalate binds with calcium to form an insoluble precipitate, which is an irreversible action. This makes it unsuitable for coagulation studies.

Visual 1: Diagram - An infographic showing the common types of blood collection tubes (vacutainers). Each tube should be color-coded (light blue, lavender, green, gray) and labeled with its specific additive (Citrate, EDTA, Heparin, Oxalate/Fluoride) and primary laboratory use (Coagulation, Hematology, Chemistry, Glucose).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anticoagulants in blood collection tubes for laboratory testing as background academic context rather than a clinical decision trigger.
Using the correct blood collection tube for the specified test is a critical nursing responsibility to ensure patient safety and prevent diagnostic errors.
A pre-analytical error, such as drawing blood in the wrong tube, will lead to rejection of the sample by the laboratory, delaying diagnosis and treatment.
What if? If a nurse draws blood for a PT/INR test into a lavender-top (EDTA) tube instead of a light blue-top (citrate) tube, the lab will report a critically high or unmeasurable INR. This could lead to a dangerous clinical decision, such as withholding a necessary anticoagulant, if the error is not caught. The sample would be rejected, and a redraw would be required, delaying patient care.

How to Approach the Question

This is a factual recall question that tests your knowledge of laboratory procedures.
First, identify the key terms in the question: 'anticoagulant' and 'coagulation testing'.
Recall the different types of blood collection tubes, their cap colors, and the additives they contain.
Associate 'coagulation testing' (e.g., PT, aPTT, INR) with the light blue-top tube.
Remember that the additive in the light blue-top tube is sodium citrate.
Evaluate the other options: EDTA is for hematology (lavender top), Heparin is for chemistry (green top), and Oxalate is for glucose testing (gray top). This confirms that citrate is the correct choice.

Concept Tested & Keywords

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