Is the Packed Cell Volume (PCV) Reliable

The reliability of the packed cell volume (PCV) has received far less scrutiny than that given to the reliability of hemoglobin and red cell count measurements. The availability of a reference PCV method allowed us to examine 12 different capillary tubes available from scientific supply houses. Our goal was to determine if PCVs obtained in these tubes were of adequate accuracy to allow the PCV to perform its calibration and quality control functions in the clinical laboratory. We confirmed that several sources of error exist in the routine laboratory performance of the PCV. Fortunately, these errors compensate for each other in the usually encountered hematocrit range. The majority of the tubes with internal diameters >1.0 mm, when used with normal blood samples, produced PCV results with biases of less than half a PCV unit. Of the 12 brands of capillary tubes evaluated, 10 were deemed “acceptable” by comparison to reference methods. Using these 10 acceptable tubes, the mean bias at PCV 0.3 was 0.004 ± 0.0011 (95% confidence limits); mean bias at PCV 0.4 was 0.001 ± 0.0012; and mean bias at PCV 0.5 was ‐0.002 ± 0.0014. The cards commonly used to read PCV values introduce significantly more irreproducibility. The smallest marked interval (0.01) commonly used on PCV reading cards is 5 to 10 times greater. Lab. Hematol. 2001;7:191‐196