The Man Behind the Curtain
The pioneer of the modern CBC was not a brilliant physician or famous scientist but instead an innovative engineer named Wallace H. Coluter; a man who stumbled into the world of hematology. In the mid-20thcentury, the United States Navy encountered a problem while preparing their battleships. They noticed that different batches of the same colored paint had slightly different tones to it. For an organization that prides itself on perfection this was unacceptable. To correct this problem, the Office of Naval Research hired Coluter to come up with a solution. Coulter quickly and astutely figured out that the key to the solution was to standardize both the number and size of the paint particles to ensure every batch of paint came out identical (1). To do this, Coulter created an instrument that could repeatedly measure particle concentrations accurately.
While there is still debate as to exactly how he fell into the medical field, while making his instrument for the Office of Naval Research, Coluter realized that the principals behind his technology could be applied to the medical field to help differentiate the different particles in blood. After the production of his first instrument, the Office of Naval research not only used his product for their original intent, but they also distributed it to several large medical institutions around the country. Soon thereafter, Coluter’s name and invention spread throughout the field of hematology. For the very first time, the medical field had an automated way of differentiating and counting certain blood cells. Over the span of 40 years, Coluter continued to expand his process and make alterations to his original machinery. The outcome was a method to distinguish and count particles of identical size but different composition, the very principal we still use today for our CBC with differential (1).
How do we even interpret this?
The CBC can be a difficult test to interpret and even more so when a differential is added to it. If you find yourself shrugging your shoulders not knowing what to make of the results, the table below may be of use. This table is by no means complete but rather it serves to highlight some of the more important, and sometimes interesting, diagnoses that are relevant for the Emergency Room physician.
A 67-year-old male with a PMH of CAD, HTN, HLD, and obesity comes into the ED for abdominal pain that has been going on for 36 hours. He is currently complaining of 8/10, generalized abdominal pain associated with nausea and vomiting. His wife is at bedside who states she brought him into the ED because he has been extremely weak at home and does not seem like himself. He denied any fevers, chest pain, shortness of breath, hematemesis, hematochezia, dysuria, urinary frequency.
VS: T 37.8, P 98, BP 135/90, RR 20, SaO2 98% on RA
Physical exam: Elderly obese male sitting up at beside who was nontoxic in appearance but appeared extremely uncomfortable. GCS 14 (-1 for confusion) but able to follow commands and move all extremities. Cardiopulmonary exam normal. Mildly tender abdomen to palpation in all four quadrants with no rebound or guarding. Mild CVA tenderness to the right. Skin warm and dry to the touch.
Na: 131 WBC: 13.3 Neutrophil #: 11,799 Lactate: 2.0
K: 4.2 RBC: 4.46 Bands: 12% Hepatic: normal
Cl: 97 Hb: 13.6 Lymphocyte #: 466 Lipase: normal
CO2: 20 Hct: 39.9 Monocyte #: 1202 VBG: normal
BUN: 2.7 Platelets: 179 Eosinophil #: 27
Cr: 2.65 Basophil #: 27
Urinalysis: cloudy color with negative nitrite but moderate leukocytes and 54 WBC
CT abdomen and pelvis: multiple obstructing calculi in the right distal ureter
The diagnosis of sepsis is not always straightforward. Many factors such as age, immune status, and timing of presentation can make matters more difficult. Tools such as the SIRS criteria and qSOFA have been used in the Emergency Department to help aid in diagnosis but are far from perfect. To optimize the chances of making this diagnosis, we should use every tool we have available to us. One such tool that is readily available is the differential that comes with the CBC. While “obvious” signs such as an elevated white count or neutrophil count may direct you towards the diagnosis of sepsis, neither of these markers are reliable (6). However, there are several hidden gems in the differential (namely things like lymphocyte count, band count, and neutrophil to lymphocyte count ratio), that can help clue you in to the diagnosis (6). Retrospective studies have shown that lymphocytopenia < 1,000 and a NLCR >10 are more sensitive markers for both gram negative and gram positive sepsis than total white blood cell count and neutrophil count (7). Other prospective studies have found that bandemia > 10 have an increased likelihood ratio for predicting systemic infection compared to the white count alone (8). While none of these markers are perfect alone, they show that the differential can provide extra clues that would otherwise go unnoticed in a potentially sick patient who needs emergent resuscitation.
Robinson, J. P. (2013), Wallace H. Coulter: Decades of invention and discovery. Cytometry, 83A: 424-438.
George Gay, B., Parker, K. (2003). Understanding the complete blood count with differential. J Perianesth Nurs, Apr; 18(2):96-114
Chernecky, C., Berger, BJ. Laboratory Tests and Diagnostic Procedures. Saunders, Philadelphia, PA (2001).
Holland, M., et al. Eosinopenia as a marker for mortality and length of stay in patients admitted with exacerbations of chronic obstructive pulmonary disease. Respirology, 2010 Jan; 15(1): 165-7
Bolayir, A., et al. The Effect of Eosinopenia on Mortality in Patients with Intracerebral Hemorrhage. J Stroke Cerebrovasc Dis, 2017 Oct; 26(10):2248-2255.
Marik, PE. Don’t miss the diagnosis of sepsis! Crit Care, 2014 Sep 27; 18(5): 529.
De Jager, CP., et al. Lymphocytopenia and neutrophil-lymphocyte count ratio predict bacteremia better than conventional infection markers in an emergency care unit. Crit Care, 2010; 14(5): R192
Cavallazzi, R. Is the band count useful in the diagnosis of infection? An accuracy study in critically ill patients. J Intensive Care Med, 2010 Nov-Dec; 25(6): 353-7.