Evaluation of unexplained leukocytosis

What it is

Leukocytosis is a relatively common finding with many possible etiologies. The white cell count is read against a normal of 4500-11,000, so a WBC count of 12,500/mm3 is leukocytosis.

It is unexplained leukocytosis when nothing in the history or the rest of the workup accounts for it. The worked case is an obese 37-year-old female seen for fatigue, otherwise asymptomatic, with normal vital signs and a physical examination unremarkable apart from the obesity; the CBC shows no anemia but a WBC of 12,500/mm3; the TSH level and a comprehensive metabolic panel are normal; she takes no medications and has had no recent illnesses. Each of those negatives is doing work: medications, recent illness, the TSH and the metabolic panel have each been looked at and found clear before the count is called unexplained.

The benign cause that may explain it

Obesity can cause leukocytosis. The paper cited for it is on leukocytosis in obese individuals, a possible link in patients with unexplained persistent neutrophilia, so what the material ties to obesity is a persistent neutrophilia rather than any raised count.

But obesity is only allowed to explain the count when nothing else is asking to be explained. In this patient it would not be appropriate at this time to attribute the leukocytosis to obesity alone, because of the fatigue. That is the whole point of the case: a benign cause that fits the white cell count does not cover a symptom that stays unexplained, and the symptom keeps the evaluation open.

Infection is the other cause weighed, and it is treated the same way: blood cultures are not necessary in cases of leukocytosis without evidence of infection. So infection is ruled out by the absence of evidence for it, not by a culture in every patient with a high count.