AIIMS CRE, SNO-2024: Hemoglobin is measured using which sample type?

AIIMS CRE, SNO-2024

Biochemistry & Nutrition

Medium

Appeared in: AIIMS CRE, SNO-2024

Explanation

Hemoglobin is a protein located entirely inside red blood cells (RBCs), which are responsible for oxygen transport.
To measure hemoglobin, the laboratory requires a sample that includes the intact red blood cells.
Whole blood is the only sample type listed that contains all cellular components, including RBCs, suspended in plasma.
During the test, the RBCs in the whole blood sample are lysed (broken open) to release the hemoglobin for measurement.
The sample is collected in a tube with an anticoagulant (e.g., EDTA) to prevent clotting and preserve the cellular components.

Option A: Serum is the liquid part of blood after it has clotted. The red blood cells, which contain hemoglobin, are removed as part of the clot.
Option C: Plasma is the liquid portion of unclotted blood from which the cells have been removed by centrifugation. Since it is cell-free, it does not contain the red blood cells necessary for a hemoglobin measurement.
Option D: Distilled water is purified water, not a biological sample from a patient. It has no clinical use for measuring blood components.

Visual 1: Diagram: An infographic illustrating the difference between whole blood, plasma, and serum. It would show a test tube of whole blood, then show it separated by centrifugation into plasma and packed cells, and a third tube showing serum separating from a clot.
Visual 2: Image: A picture of different color-coded vacutainer tubes, highlighting the lavender/purple top tube used for collecting whole blood (with EDTA anticoagulant) for a Complete Blood Count (CBC).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Appropriate blood sample type for hemoglobin measurement as background academic context rather than a clinical decision trigger.
Patient Safety: Using the correct sample type is critical for accurate laboratory results. An incorrect sample (e.g., using serum for a hemoglobin test) would lead to a failed test or a dangerously inaccurate result, potentially masking a condition like severe anemia or polycythemia.
Nursing Responsibility: Nurses are responsible for collecting blood samples using the correct vacutainer tube for the ordered test. Knowing that a CBC or hemoglobin test requires a lavender-top (EDTA) tube for a whole blood sample is a fundamental nursing skill.
What if? If a nurse accidentally draws blood for a CBC into a serum-separator tube (SST), the blood will clot. If this clotted sample is sent to the lab, it cannot be used for a CBC. The lab will reject the sample, and the patient will need to undergo another venipuncture, causing delay in diagnosis and treatment, and unnecessary discomfort.

How to Approach the Question

Step 1: Identify the substance being measured. The question asks about measuring 'hemoglobin'.
Step 2: Recall the location of this substance in the body. Remember that hemoglobin is the main component inside red blood cells (erythrocytes).
Step 3: Analyze the options based on this knowledge. Evaluate each sample type to see if it contains red blood cells.
Step 4: Eliminate incorrect options. Serum and plasma are liquid components from which red blood cells have been removed (either by clotting or centrifugation). Distilled water is not a biological sample.
Step 5: Select the correct option. Whole blood is the only option that contains all the components of blood, including the red blood cells where hemoglobin is found. Therefore, it is the correct sample type.

Concept Tested & Keywords

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E6 Biochemistry U Satyanarayana 7th Edition — Part 1 (pp 26-420 of 840) p. 420-840