Which manual laboratory test would be most affected by using an EDTA sample that contains only about 1 mL of whole blood?

Which manual laboratory test would be most affected by using an EDTA sample that contains only about 1 mL of whole blood?

• A. ESR
• B. Hemoglobin
• C. Blood glucose
• D. Creatinine

Answer: (A)

Erythrocyte sedimentation rate depends on a precisely filled, anticoagulated blood sample in a Westergren tube. When only about 1 mL of whole blood is available in an EDTA vial, you cannot achieve the proper blood-to-anticoagulant and blood-to-diluent ratios required for the sedimentation measurement, so the height of settled cells becomes unreliable and the result is invalid. Other tests can tolerate smaller volumes or are less sensitive to the exact ratio in the sample: hemoglobin can be measured from a small aliquot, glucose can be measured on plasma but is influenced by processing time, and creatinine measurement uses plasma/serum volumes that are usually feasible even with limited blood. Thus, the manual ESR reading is the most affected by a very small EDTA sample.

Erythrocyte sedimentation rate depends on a precisely filled, anticoagulated blood sample in a Westergren tube. When only about 1 mL of whole blood is available in an EDTA vial, you cannot achieve the proper blood-to-anticoagulant and blood-to-diluent ratios required for the sedimentation measurement, so the height of settled cells becomes unreliable and the result is invalid. Other tests can tolerate smaller volumes or are less sensitive to the exact ratio in the sample: hemoglobin can be measured from a small aliquot, glucose can be measured on plasma but is influenced by processing time, and creatinine measurement uses plasma/serum volumes that are usually feasible even with limited blood. Thus, the manual ESR reading is the most affected by a very small EDTA sample.