A retrospective review of complete blood count versus complete blood count with differential orders in a community-based clinic

From the 2019 HVPAA National Conference

Dr. Meghana Parsi (Crozer Chester Medical Center), Dr. Maitreyee Rai (Crozer Chester Medical Center), Dr. Jian Liang Tan (Crozer Chester Medical Center), Dr. Alan Zweben (Crozer Chester Medical Center)


Complete blood count (CBC) is one of the most common blood tests ordered in ambulatory clinics. CBC may be ordered with “differential” in certain clinical situations or patients. There is currently no standard guideline that exists to guide physicians on ordering CBC versus CBC with differential. Often time, the differential component does not add any significant value to clinical making decision and may lead to unnecessary testing.


The primary outcome of our study included identifying the reasons for CBC with differential orders in our teaching ambulatory clinic from July-December 2018. Secondary outcomes assessed the appropriateness versus inappropriateness of these differential orders and the potential costs incurred.


A retrospective chart review was performed on any CBC with differential orders that were placed from July-December 2018 in all patients over the age of 18. Exclusion criteria included any CBC order that did not include a differential in the time outlined.


A total of 988 CBC with differential were ordered over a period of six months. Out of 988, 49% (481/988) were ordered by the residents and 51% (507/988) by the attending physicians. Only 19% (183/988) of the orders were deemed appropriate as per an article published by Rich et al1 (Table 1) and 81% (805/988) of the orders were considered unnecessary.

The common indications for ordering CBC with differential are included in table 2. The top three inappropriate indications for ordering CBC with differential include 32.2% (318/988) for preventative health care, 13.1% (130/988) for anemia evaluation, and 11% (109/988) for new patient evaluation. Out of the 183 appropriate orders, only 138 had abnormal differential results. However, only 49% (68/138) of these abnormal results were acknowledged and received further workup. Out of these, 32% (60/138) had a clinically significant diagnosis or treatment change. These results are included in table 3. 57%(78/138) of the abnormal results were deemed false positive. In summary, of all the differential orders placed, an abnormal differential was clinically significant in only 6%(60/988) of the patients.


In our study, we found the physicians in our ambulatory clinic often inappropriately ordered the CBC with differential and more than half of the abnormal result were not addressed in a timely manner. Overutilization of CBC with differential remains an active issue yet to be tackled at our ambulatory clinic.

Implications for patient care

  1. The cost of CBC and CBC with differential at our local laboratory is $22 and $24, respectively. Though the difference is only $2, the costs add up at a population level. In the year 2017, Medicare spent an average of $305 million on 29 million CBC with differential orders and $29 million on 3 million blood counts (without differential) 2. Based on our study, if the top three non-indicated differential orders are eliminated (56%), cost savings could be approximately $134 million.
  2. Abnormal test result often led to unnecessary re-testing or additional work up. Hence, a multifaceted quality improvement project on CBC with differential has currently been undertaken by the residents to improve the number of inappropriate tests.


  1. Rich, Eugene. (1983). Effectiveness of Differential Leukocyte Count in Case Finding in the Ambulatory Care Setting. JAMA: The Journal of the American Medical Association. 249. 633. 10.1001/jama
  2. Centers for Medicare and Medicaid Services. Part B National Summary Data File. Available at: https://www.cms.gov/Research-Statistics-Data-and-Systems/Downloadable-Public-Use-Files/Part-B-National-Summary-Data-File/Overview.html


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