WBC Decrease in Infection

Clinical Presentation

In neutropenic patients, WBC count cannot be used as a criterion to define sepsis because these patients lack the ability to mount a leukocytosis response, as stated by the National Comprehensive Cancer Network 1, 2
Approximately 50-60% of febrile neutropenic patients have an established or occult infection despite their low WBC count, according to the National Comprehensive Cancer Network 3
The absence of granulocytes means signs and symptoms of infection are often absent or muted, though fever remains an early sign, as noted by the National Comprehensive Cancer Network 3
Influenza A commonly causes low WBC count in children, with lymphopenia, as reported by the Thorax journal 4
In H5N1 cases, all seven children had WBC <4.0 and 6/7 had lymphopenia <1.0, with six of seven dying, according to the Thorax journal 4
A raised WBC (>15) is found in only 8-12% of influenza cases, as stated by the Thorax journal 4

Fever remains an early sign even when WBC cannot rise, as noted by the Journal of the National Comprehensive Cancer Network 3
Focus on other inflammatory parameters: C-reactive protein, procalcitonin, fever, hypothermia, tachycardia, tachypnea, as recommended by the Annals of Oncology 1, 2
Blood cultures should be obtained, as 10-20% of patients with neutrophil counts <100/μL will develop bloodstream infection, according to the Journal of the National Comprehensive Cancer Network 3

Do not assume absence of infection based on low or normal WBC count - bacterial infections can present with leukopenia, particularly in early phases or severe disease, as warned by the Thorax journal 4
Do not delay antibiotics in neutropenic patients awaiting WBC rise - these patients cannot mount a leukocytosis response, as advised by the Annals of Oncology 1, 2
Recognize that low WBC in viral infections (especially influenza) is common and expected, not a sign of bacterial superinfection unless other criteria are met, as stated by the Thorax journal 4