Optimization of Laboratory Ordering Practices for Complete Blood Count With Differential

Jeffrey Z. Shen; Benjamin C. Hill, MD; Sherry R. Polhill, MBA, MT(ASCP); Paula Evans, MT(ASCP); David P. Galloway, MD; Robert B. Johnson, RRT, MS; Vishnu V.B. Reddy, MD; Patrick L. Bosarge, MD; Lisa A. Rice-Jennings, MT(ASCP); Robin G. Lorenz, MD, PhD


Am J Clin Pathol. 2019;151(3):306-315. 

In This Article

Abstract and Introduction


Objectives: To investigate the utilization of CBC and CBC with differential (CBC w/diff) tests at University of Alabama at Birmingham Hospital, and to determine if a reduction in CBC w/diff tests could be achieved without negatively impacting patient care.

Methods: The quantity of testing and distribution of repeated tests before, during, and after an educational intervention were compared.

Results: CBC w/diff tests were ordered 10-fold more frequently than CBC tests. The trauma burn intensive care unit ordered the most CBC w/diff tests, with repeat tests done every 4 or 12 hours. The educational intervention reduced the number of CBC w/diff tests ordered and tests repeated every 12 hours.

Conclusions: The educational intervention changed the ordering practices of CBC w/diff and CBC tests. This was sustained after the intervention and no negative effects on patient care were noted. Similar interventions may lead to optimization of ordering practices of other laboratory tests.


Health care expenditures are estimated to rise to $3.6 trillion in 2018,[1] with accelerated growth in hospital spending and spending on physician and clinical services. Excess health care costs are estimated to be $750 billion, and are caused by unnecessary services, inefficient delivery of services, high prices, excess administrative costs, missed prevention opportunities, and medical fraud. Out of these six reasons, unnecessary services are the largest contributor to excess health care costs.

More than 5 billion laboratory tests are performed each year, over 20% of which have been reported to be unnecessary.[2] In 2012, the American Board of Internal Medicine Foundation initiated the Choosing Wisely campaign to increase awareness of wasteful or unnecessary medical tests, procedures, and treatments.[3,4] More than 70 individual medical and physician societies are now participating in the Choosing Wisely[3] campaign and have released recommendations designed to reduce these wasteful and unnecessary tests.

Often tests are ordered routinely without a clear rationale. Not only do these routine tests increase health care spending but are also a source of iatrogenic blood loss and anemia in hospitalized and critical care patients.[5] Hospital-acquired anemia has been associated with increased blood transfusions (and the subsequent increased exposure to infection), as well as increased length of stay and mortality.[6] It has been estimated that it would only take 9 to 14 days of routine blood draws to take a critical care hospitalized patient below the RBC transfusion threshold.[5,7]

Because of its wide-reaching potential for disease diagnosis, the complete blood count (CBC) and complete blood count with differential (CBC w/diff) tests are, respectively, the first and second most performed tests in the clinical hematology laboratory.[8] Choosing Wisely[3] recommends eliminating repetitive CBC and chemistry testing for clinically stable patients. However, in investigating repeat testing, it has been suggested that the CBC w/diff test should only be ordered if there are symptoms or risk of anemia, if the patient is bleeding or at risk of bleeding due to a pending surgical intervention or procedure, if there are signs of infection, if the patient has a disease that affects blood cells, or if the patient is receiving a treatment that would affect blood cells.[8,9] Along with evaluating the rationale for ordering the CBC w/diff test, the frequency at which the test is repeated should be determined. This frequency can be estimated by the time it takes for the last neutrophil progenitor to be released in the blood as a neutrophil, because neutrophils have the shortest half-life of the cell types analyzed by the CBC w/diff test. Multiple studies in both animals and humans have estimated that this time is 6 to 7 days when an individual is healthy, and 2 days in diseased individuals.[10]

Based on these data, several studies have defined the criteria for appropriate ordering of the CBC w/diff test for both initial test ordering and repeated testing. In 1989, the criteria for appropriate CBC w/diff initial testing included: emergency admission, a temperature of greater than 38.0°C, suspected infection, primary hematologic disorder (ie, anemia, myeloproliferative disorder, aplasia, platelet disorder), anticipation of a therapy toxic to the bone marrow, or suspicion of disorders associated with eosinophilia, monocytosis, lymphocytosis, or basophilia.[11] A second study, completed in 1984, evaluated the utility and cost effectiveness of the CBC w/diff test among inpatients.[12] The criteria in this study for a justified order for a CBC w/diff test included those listed above for initial ordering, as well as any new symptom arising in the hospital that was potentially a manifestation of an infection or a hematologic process that was recorded in the chart by the physician and a follow-up of an increased WBC count (>11,000/μL) or a decreased WBC count (<4,000/μL). To determine the criteria used to determine if there is a clinically significant change in the results from a repeated CBC w/diff test, a retrospective cohort study was performed in 1998.[13] This study defined a redundant CBC w/diff test as one done within 36 hours of a previous CBC w/diff test (except for patients in which treatment was based on the differential, ie, a cancer patient with neutropenia). The United Kingdom has issued national minimal retesting interval guidelines, which state that repeat CBC (without diff) testing should have a minimum interval of once daily for unstable patients without active bleeding or receiving cytotoxic drugs and once in 4 days for stable patients.[14] Indications for repeat CBC include clinically significant changes such as a massive hemorrhage, in which it is appropriate to order a CBC every hour to check on the patient's status.

Furthermore, one study from the University Hospitals of Cleveland indicates that 90% of physicians report that they only routinely used four of 11 parameters of the CBC with/diff.[15] These were hemoglobin, hematocrit, platelet count, and WBC count. These are all parameters reported in the basic CBC test, and this indicates that most physicians do not use the majority of additional data reported in the CBC w/diff test analysis. Therefore, it is possible that many CBC w/diff tests are ordered when the rationale for a CBC test, but not CBC w/diff test, is met.

Several types of interventions have been evaluated to determine their impact on optimizing laboratory ordering practices; however, the results of these studies are often inconsistent. Educational methods, such as flyers and periodic email reminders, have attempted to encourage ordering of blood tests by internal medicine providers only if the results would change management. This approach successfully reduced average daily ordering of CBC and basic metabolic panel (BMP).[6] Another study used lectures on appropriate utilization of laboratory tests for residents in an outpatient clinic, and their results demonstrated a reduction in the total number of ordered tests.[16] There also have been successful approaches that incorporate multiple different methods, including education, intensive care unit (ICU) rounds checklists, and electronic medical record interventions to only allow ordering of tests for accepted indications.[17]

Several studies have shown that residents order more redundant testing than the faculty attendings, which has been attributed to lack of education on appropriate laboratory testing and knowledge of costs for ordering laboratory tests.[18,19] Interventions specifically focusing on improving resident education have been successful in reducing redundant laboratory testing.[20–22] However, there is little research on interventions focused on changing physician ordering from one test to another more appropriate test.

Therefore, our team designed a study to determine if a reduction in CBC w/diff test frequency could be achieved, without negatively impacting patient care by delaying diagnosis of sepsis. By analyzing data on laboratory ordering patterns of CBC and CBC w/diff tests in the electronic medical records, our team created a process map of how laboratory tests were currently ordered in our ICUs and then utilized this information to determine the top reasons that contributed to overutilization of CBC w/diff testing. We then investigated the effects of an educational intervention at one unit of University of Alabama at Birmingham (UAB) Hospital on the quantity of tests, practices of repeat testing, as well as appropriate test ordering (CBC tests instead of CBC w/diff tests in cases when the differential is not needed or used).