White Blood Cell Counts - Clinical Knowledge GapsWhen You Might Not Know About WBC Counts
White blood cell counts serve three purposes...
The most important purpose of WBC counts is to determine at the time of presentation, whether the counts are elevated or reduced when evaluating a patient with an acute illness.
Secondly, the white blood cell counts serve to monitor the improvements in the process of treatment.
Thirdly, the differential of the white cell count serves to screen for abnormalities during a health examination.
The bone marrow has a reserve of mature neutrophils that may be 10-20 times the number present in the circulation.
There is also a reservoir of mature neutrophils in the spleen.
Thus, where an elevated neutrophil count is due to an infectious or inflammatory disorder (not a myeloproliferative disease or disturbed marrow function), the cells are all mature (no band neutrophils or metamyelocytes) due to mobilization from these mature reservoirs. The maturity of the neutrophils is an important differential feature.
Due to the substantial marrow reserve, it is not unusual to see white blood cell counts at high as 100,000/mm3 in patients after a strong stimulus such as corticosteroids, lithium, severe stress or post-splenectomy, and after chemotherapy induced bone marrow suppression.
In contrast, myeloproliferative disorders such as chronic myelogenous leukemia or disturbances of the marrow architecture such as metastatic carcinoma to bone, result in the presence of immature neutrophils in the peripheral blood (bands, metamyelocytes, occasional myelocytes, even nucleated red blood cells).
For many years, white blood cells were thought to remain in the circulation for only a few hours. It is now known that they may remain viable in the circulation for a number of days before being extruded into soft tissue.
Chronic leukocytosis, on the other hand, may result from a hereditary disorder known as leukocyte adhesion deformity; a disorder where the white cells are not able to respond to a local stimulus such as a site of infection or inflammation.
Hereditary neutrophilia is a rare autosomal dominant disorder.
Finally, when the rare patient with chronic neutrophilic leukocytosis is followed over a long period and no cause is ever identified, the diagnosis of chronic idiopathic neutrophilia is applied.
Lymphocytosis is defined as a lymphocyte count above 5000/mm3.
Viral diseases such as Epstein-Barr virus infection are the most common reasons for benign lymphocytosis in the context of infection.
However, when the majority of white blood cells are lymphocytes, a blood smear should be obtained to, among other examinations, determine the presence/absence of immature lymphocytes.
Immature lymphocytes indicate either acute lymphoblastic leukemia or lymphoblastic lymphoma. On the other hand, a preponderance of mature lymphocytes suggests chronic lymphatic leukemia.
Eosinophilia is defined as an eosinophil count of greater than 400/mm3. An increase in eosinophils is most often associated with allergic reactions (external allergens, drug reactions. Inflammatory disorders such as granulomatosis with polyangiitis, some parasitic infections, and occasional cancers will be found to be accompanied by eosinophilia.
Berliner N. Leukocytosis and Leukopenia. Goldman-Cecil Medicine, 2020; 158: 1094-1103.e2
Figure 1. White Blood Cell Count Reference Chart
Figure 2. Leukocytosis Algorithm (https://www.aafp.org/afp/2015/1201/p1004.html)
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