The Complete Blood Count with Differential (CBC-Diff) is a first line laboratory test ordered in the Emergency Department.1 The CBC-Diff report is generated by an automated hematology analyzer and provides insights about the immune system through various leukocyte parameters. Further information can be gleaned by considering leukocyte parameters in relationship to each other. For example, the ratio of neutrophils to lymphocytes can suggest a dysregulated immune response.
Understanding the synergies of the differential parameters may provide valuable diagnostic information at no additional cost and with no additional time.
In this single-center retrospective study, scientists analyzed vital signs and lab results from over 50,000 Emergency Department patients to create a simple 5-point sepsis screening tool, the CBC Index, to reliably estimate the likelihood that a patient will develop sepsis.
Logistic regression identified four differential parameters (white blood cell, lymphocyte and neutrophil counts, and Monocyte Distribution Width) that, when considered together, significantly increased early sepsis diagnostic performance. WBC count elevation is associated with host response to infection but as a standalone parameter, has limited utility for sepsis screening due to low specificity and sensitivity. The Neutrophil to Lymphocyte Ratio (NLR) is known to increase with physiological stresses, including those experienced during sepsis. Moreover, sepsis can stimulate apoptosis (programmed cell death) in lymphocytes2,3 and thus cause the NLR to increase. More recently, MDW, a measure of the morphological changes associated with monocyte activation, has emerged as an integral component of the CBC for early identification of sepsis.4,5
An index score was derived from patient data and applied to a validation cohort that included patients without sepsis, with overt sepsis presentation, and with occult sepsis presentation.
The study found:
- The composite CBC Index, a combination of WBC count, MDW, and NLR, showed superior diagnostic performance in early sepsis detection over any single parameter, especially in the occult group
- There was a linear relationship between the CBC infection severity index and likelihood that a patient would develop sepsis or septic shock