OBJECTIVE: To define the sensitivity and specificity of stone gram stain for infected urolithiasis treated with percutaneous nephrolithotomy (PCNL).
METHODS: PCNL procedures performed at our institution were analyzed between January 2009 and May 2013. Stone fragments were sent in a sterile fashion for aerobic and fungal cultures. A gram stain and fungal smear were performed on the stones and reported within 24 hours of collection.
RESULTS: A total of 228 patients underwent 248 PCNLs. Of the 248 stones, 81 (33%) had a positive stone culture. Stone gram stain was positive in 31 cases and negative in 50. There were 167 negative stone cultures, and in these cases, gram stain was positive in 5 and negative in 162. The calculated sensitivity and specificity of stone gram stain were 38% and 97%. The positive and negative predictive values were 86% and 76%, respectively. In the subset of 16 patients with positive stone fungal cultures, fungal smear was performed in 12 and was positive in 4, giving fungal smear a sensitivity of 33%.
CONCLUSION: The results of this study suggest that stone gram stain cannot be relied on to detect a positive stone culture and may fail to detect up to 62% of infected stones. However, when positive, gram stain accurately predicts a positive stone culture in 86% of cases.
Written by:
Cockerill PA, Rivera ME, Krambeck AE. Are you the author?
Department of Urology, Mayo Clinic, Rochester, MN. Krambeck.
Reference: Urology. 2014 Mar 5. pii: S0090-4295(14)00016-8.
doi: 10.1016/j.urology.2013.12.043
PubMed Abstract
PMID: 24612614
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