Initial Laboratory Workup for Leukocytosis

Initial Assessment

The American College of Physicians recommends a complete blood count (CBC) with differential as the first essential test to characterize the leukocytosis and identify which cell line is elevated, with a strength of evidence based on multiple citations 1, 2
Peripheral blood smear review is recommended to examine morphology of white blood cells, assess for left shift (increased band neutrophils), and rule out malignant cells, according to the Infectious Diseases Society of America 1, 2
A comprehensive metabolic panel is suggested to monitor for potential tumor lysis syndrome and assess organ function, as recommended by the American Society of Clinical Oncology 3

An elevated total band count (>1500/mm³) has the highest likelihood ratio (14.5) for detecting bacterial infection, according to the Infectious Diseases Society of America 1
Increased percentage of neutrophils (>90%) and band neutrophils (>16%) have likelihood ratios of 7.5 and 4.7, respectively, for bacterial infection, as reported by the Clinical Infectious Diseases journal 1
A WBC count >14,000 cells/mm³ has a likelihood ratio of 3.7 for bacterial infection, based on evidence from the Clinical Infectious Diseases journal 1, 2

Flow cytometry should be considered if lymphoproliferative disorder is suspected based on morphology, as recommended by the American Society of Clinical Oncology 3

Urinalysis and urine culture are recommended if urinary symptoms are present or if source of infection is unclear, according to the Infectious Diseases Society of America 1, 4
Blood cultures are suggested if systemic symptoms or signs of sepsis are present, as recommended by the Clinical Infectious Diseases journal 4
Respiratory evaluation (including chest imaging) is recommended if respiratory symptoms are present, based on evidence from the Clinical Infectious Diseases journal 4
Consider CT imaging for suspected intra-abdominal infections, as suggested by the Clinical Infectious Diseases journal 4

Leukocytosis without fever does not exclude infection, particularly in older adults, according to the Infectious Diseases Society of America 1, 2
Treating asymptomatic patients with antibiotics based solely on mildly elevated WBC counts can lead to unnecessary antibiotic use, as reported by the Praxis Medical Insights 2, 4

Overlooking the significance of absolute neutrophil count elevation when total WBC count is only mildly elevated, as noted by the Praxis Medical Insights 2