Automated leukocyte differential counters.

The leukocyte or white blood cell (WBC) differential count has been an established laboratory examination for almost a century. In recent years, the number of clinicians' requests for the test has grown steadily, and presently over 1,000,000 WBC differentials are performed daily in the United States. The manual WBC differential count requires tedious and repetitious cell classification, which is prone to subjective bias. Quite understandably, the WBC differential count has been a prime candidate for automation. Manufacturers have developed automated WBC differential counters that are accurate and that more precisely classify WBCs than do experienced morphologists. However, the WBC differential count, initially controversial because of technologists' subjective cell classification, has again become an object of debate following the substitution of automated instruments to perform cell identification. Instead of significantly better test results, automated WBC differential counters have demonstrated that variables inherent in the methodology, which cannot be controlled by automated techniques, limit the validity of information derived from the WBC differential. This report discusses the issues surrounding the use of automated WBC differential counters that need to be addressed by those contemplating acquisition of the technology. More fundamental questions are also explored, i.e., if the acknowledged clinical utility of the WBC differential in its present status is limited, what alternatives are available, and is investment in the currently available technology prudent?