The Demise of the Eyecount Leukocyte Differential

Peripheral blood film review refers to checking or verifying flagged or abnormal results obtained by an automated hematology analyzer. The usual mechanism for this review is to have an expert human inspect a stained blood film with identification and enumeration of 100 or more consecutive leukocytes. This function also includes inspection of red cell and platelet morphology with comments and interpretation of the findings, when indicated. Before the introduction of automated leukocyte differential instruments, it was common practice to prepare, stain, and examine a blood film and perform a 100or 200-cell eyecount leukocyte differential count (ECLDC) on all samples submitted for a complete blood count (CBC), whether done by old-fashioned manual techniques or modern automated hematology analyzers. This practice was labor intensive requiring highly trained technologists, and added greatly to the cost of providing laboratory results. This practice took place because it was a widely held belief that it was necessary, to prevent significant errors caused by false-negative results by the instruments. The complete blood cell count and leukocyte differential count traditionally have been the highest volume tests in the clinical laboratory. Today, the common laboratory practice is to review only those specimens from the automated instruments that are flagged for review, because of distributional, morphologic, or instrument failure flags. Numerous studies have documented that this approach can markedly reduce the costs of the CBC and leukocyte differential, and provide greater sensitivity for detection of abnormalities of the CBC and leukocyte differential.1, 5 The following issues are covered in this article: