If a 7.0-mL EDTA tube contains only 2.0 mL of blood, which test will likely be erroneous?

In a scenario where only 2.0 mL of blood is present in a 7.0-mL EDTA tube, the hematocrit (Hct) test is the most likely to yield erroneous results. Hematocrit is a measure of the proportion of blood volume that is occupied by red blood cells. It is calculated based on the volume of cells to the total volume of the sample.

When the sample volume is significantly less than required, the overall concentration of red blood cells can be misinterpreted, as there may not be enough blood to accurately determine the true proportions of cellular components. Low sample volume can lead to skewed calculations, especially with hematocrit, where an accurate measurement requires a sufficient volume for proper separation and volume measurement of the packed cells.

In contrast, while RBC count, hemoglobin, and WBC count can also be affected by sample volume, they are generally less susceptible to distortion in smaller volume samples than hematocrit calculations are. RBC and WBC counts can still provide some degree of accuracy because they assess individual cell counts, while hemoglobin concentration can often be estimated reliably even with lower sample volumes due to less dependence on total volume.