Which vial is generally used for collecting blood samples for plasma glucose estimation?

RML PRE 2025

Biochemistry & Nutrition

Easy

Appeared in: RML PRE 2025

Explanation

Sodium fluoride is the correct additive for plasma glucose estimation because it acts as a glycolysis inhibitor.
It specifically inhibits the enzyme enolase in the glycolytic pathway, preventing red blood cells from consuming glucose in the sample after it has been drawn.
This action is crucial because it ensures the measured glucose level accurately reflects the patient's blood glucose at the time of the draw, preventing falsely low results.
Blood for glucose testing is typically collected in a grey-top tube, which contains sodium fluoride and an anticoagulant like potassium oxalate.

Option A: EDTA is an anticoagulant that prevents clotting by chelating calcium, but it does not stop the metabolic process of glycolysis. Therefore, glucose levels in an EDTA tube will decrease over time, leading to inaccurate results for glucose estimation.
Option B: Heparin is an anticoagulant that works by inhibiting thrombin, but like EDTA, it does not have antiglycolytic properties. It is unsuitable for routine glucose testing as glucose degradation will occur.
Option C: Sodium bicarbonate is a buffer used therapeutically to manage conditions like metabolic acidosis. It is not used as a preservative or anticoagulant in standard blood collection tubes.

Clinical Relevance

Nursing practice connection: Knowing Additives in blood collection vials for specific laboratory tests helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Using the correct blood collection vial is a critical pre-analytical step for ensuring accurate diagnostic test results. A sample drawn in the wrong tube can lead to erroneous results, misdiagnosis, and inappropriate patient treatment.
For a diabetic patient, an inaccurately low glucose reading (due to glycolysis in the wrong tube) could lead to a missed diagnosis of hyperglycemia or an incorrect assessment of glycemic control, impacting insulin dosage and management.
What if? If a sample for glucose testing was accidentally collected in a heparin (green-top) tube and there was a 2-hour delay before analysis, the glucose value would be falsely low by approximately 20 mg/dL because glycolysis would continue unchecked.

How to Approach the Question

First, identify the key test mentioned in the question: 'plasma glucose estimation'.
Second, recall the specific requirements for this test. Glucose is a labile analyte that is consumed by blood cells after collection (a process called glycolysis), so a special preservative is needed to stop this process.
Third, evaluate the options based on their primary function. Consider which additive acts as an antiglycolytic agent.
Recognize that EDTA and Heparin are primarily anticoagulants; they prevent clotting but do not stop glycolysis.
Eliminate Sodium bicarbonate as it is not a standard tube additive for sample preservation.
This leaves Sodium fluoride, which is the classic glycolysis inhibitor used for glucose testing. Match this function to the requirement of the test to confirm it as the correct answer.

Concept Tested & Keywords

Concept Tested: Additives in blood collection vials for specific laboratory tests.
Stem keywords: blood samples, plasma glucose estimation, vial
Lead-in keywords: Which
Negative lead-in flag: false

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E6 textbook of Applied Biochemistry and Nutrition & DieteticsHarbans Lal (pp 26-464 of 479) pp. 213-215, 214-216

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart B (pp 240-463 of 478) p. 83-85