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The term hematocrit is derived from the English prefix hemato- and the Greek word krites. Hematocrit measures the volume of packed red blood cells (RBCs) relative to whole blood cells (WBCs). Hence, it is also known and reported as a packed cell volume. Hematocrit is a simple test used to identify conditions such as anemia or polycythemia and to monitor the response to treatments. A glass tube and a centrifuge machine are sufficient to measure hematocrit. After centrifugation, the blood component separates into 3 distinct parts—the bottom layer of RBCs, a middle layer of WBCs and platelets, and a top layer of plasma. This method of determining hematocrit using a Wintrobe hematocrit tube is known as the macrohematocrit method (see Image. Wintrobe Hematocrit Tube Containing Blood Components After Centrifugation).[1] The Wintrobe tube is a narrow glass tube measuring 110 mm long, with graduation from 0 to 100 mm in ascending and descending order. This method has been replaced by the microhematocrit method, which uses a small capillary tube instead of a Wintrobe hematocrit tube. The microhematocrit method requires a smaller blood sample and less time for the testing procedure, making it beneficial for patients where blood collection is difficult, such as pediatric patients or those with hypovolemia. However, the principle of the test remains the same as the macrohematocrit method. Hematocrit calculation is performed by dividing the lengths of the packed RBC layer by the length of total cells and plasma. As it is a ratio, it does not have any unit. Multiplying the ratio by 100 gives the accurate value, which is the accepted reporting style for hematocrit. For healthy adults, normal hematocrit ranges from 40% to 54% in males and 36% to 48% in females.[2] Although these 2 methods are still used in some primary care settings and medical teachings, they are widely replaced in most settings by an automated analyzer, where hematocrit reports are generated along with the complete blood count.

With the advent of automated hematology cell counters, the macrohematocrit and microhematocrit methods have become less commonly used in many clinical settings. However, these techniques remain vital in resource-poor environments where access to advanced technology may be limited. In these contexts, macrohematocrit and microhematocrit methods are essential for diagnosing conditions such as anemia and polycythemia and monitoring treatment responses. Notably, in rural healthcare facilities, the microhematocrit method is often more reliable for identifying anemia compared to total RBC counts, which are prone to significant errors in manual assessment. The microhematocrit method, in particular, offers advantages that make it suitable for mass surveys and screening programs. This method requires a smaller blood sample, which benefits patients, especially when blood volume is a concern, such as in pediatric populations or individuals with difficult venous access. In addition, the testing time for microhematocrit is significantly shorter compared to that for the macrohematocrit method, allowing for a quicker turnaround in results. This efficiency enhances the treatment of patients and facilitates timely interventions in public health initiatives, making it a valuable tool in settings where rapid diagnosis is crucial.