Repeat Meningitis/Encephalitis Syndromic Panel Testing After an Index-Negative Result: A Retrospective Laboratory-Record Study

Abstract

Syndromic molecular panels rapidly detect predefined central nervous system pathogens, but the incremental microbiological yield of repeating the same panel after an index-negative result is uncertain. We retrospectively analyzed 313 meningitis/encephalitis (ME)-panel episodes from 265 patients from September 2023 to March 2026. Among 228 patients with a first-observed index-negative panel, 30 underwent subsequent repeat testing and 198 had no subsequent repeat ME-panel test recorded at this institution during the study period. Repeat-tested patients had higher index-panel-linked cerebrospinal fluid (CSF) white blood cell (WBC) counts (median 28.0 vs. 4.0 cells/µL; p < 0.001) and protein concentrations (73.4 vs. 52.4 mg/dL; p = 0.004), whereas glucose did not differ significantly. In the 30 repeat-tested index-negative patients, no negative-to-positive conversion was observed (0/30; exact 95% confidence interval, 0.0–11.6%), and none of the 44 repeat tests detected a new on-panel target. Among 28 persistently negative patients with paired CSF WBC results, the median count decreased from 30.5 to 3.5 cells/µL. Clinical indications, treatment exposure, immune status, and final diagnoses were unavailable. These findings provide laboratory context for repeat testing but do not determine patient-level clinical appropriateness or exclude central nervous system infection.