The evolution of the complete blood count: have we gone too far?

The complete blood count (CBC) began its evolution at the end of the 19th century with the development of the hemacytometer to count blood cells. Soon thereafter, the hematocrit, a method to determine the packed red cell volume, was described in Sweden. Subsequently, the mean volume and hemoglobin content of red cells were added. Stains that distinguished individual leukocyte types permitted differential white cell counts: the product of the total white cell count and the fraction of each white cell type. A reliable means to count platelets rounded out the manual CBC. In 1954, Wallace Coulter introduced the Model A electronic particle counter. Modifications and advancements evolved into the Model S, a rapid, accurate, electronic method to determine the standard variables in the CBC and an array of additional measurements. Electronic particle counting has undergone numerous further developments including the application of florescence technology, such that approximately 30 variables can be measured as part of a CBC. This evolution has led to a chaotic situation; a recent study showed that the CBC ranged from 12 to over 24 variables when measured in either a community or academic hospital hematology laboratory. Out-of-range values, frequent and often trivial, have to be reconciled for patient and physician. Redundant and very low value variables have accrued in the CBC. We propose a major change in the CBC depending on the reason for its measurement. These recommendations markedly decrease the variables measured and make the results more impactful, which will enhance the physician's focus on the use of this key laboratory test to the benefit of the patient's care.