White Blood Cell Count Elevation Not Enough for C diff Testing

Using elevated white blood cell count alone as a predictor for Clostridium difficile (C diff) infection nucleic acid testing (NAAT) positivity is not sensitive enough and has low specificity, according to a paper published in Clinical Infectious Diseases.

Investigators from the University of Washington School of Medicine in Seattle retrospectively reviewed the laboratory testing, outcomes, and treatment of patients in order to determine a link between elevated white blood cell count and the results of C diff NAAT. The study authors noted that an elevated white blood cell count, measured at >15 thousand/μL, is an established prognostic marker for C diff patients, backed up by small observational studies. However, only limited evidence links white blood cell count elevation with the results of NAAT for C diff.

The investigators identified 16,568 consecutive patients at 4 hospitals over a span of 4 years who underwent NAAT and white blood cell count testing on the same day.

The study authors observed no significant relationship between C diff NAAT results and concurrent white blood cell count in the inpatient setting, they wrote.

They did find that an elevated white blood cell count predicted NAAT results in the outpatient and emergency department populations, though. But the accuracy was poor, they said. Additionally, the receiver-operator areas were under the curve of 0.59 and 0.56.

“Although white blood cell count is an important prognostic indicator in patients with C diff infection, an isolated white blood cell count elevation has low sensitivity and specificity as a predictor of fecal C diff NAAT positivity in the inpatient setting,” the study authors concluded. “A high or rising white blood cell count in isolation is not a sufficient indication for C diff infection testing.”

Patients with an elevated white blood cell count with C diff were linked to a longer median hospital length of stay (15.5 days vs. 11 days). The investigators also said that this finding was consistent with leukocytosis as a prognostic marker in C diff infections.

The research team also explored how these patients were treated with antibiotics. They observed that inpatients with positive NAAT results who had elevated white blood cell counts were more likely to be treated with metronidazole and/or vancomycin. They were also more likely to die in the hospital.

In October, NAAT use adjusted the estimate of total C diff infection burden from 24 percent between 2011 and 2017, as HCPLive® reported. High Point University Fred Wilson School of Pharmacy investigators made this observation while studying kidney injuries as a C diff infection disease severity marker. HCPLive also reported that while the burden decreased, estimates of the burden of first recurrence and in-hospital deaths did not significantly change during that observation period.