Introduction: Carbonate apatite (CA) stones are commonly referred to as infection stones given their formation in the presence of bacterial infection and their association with positive urine and stone cultures. Anecdotally at our institution, we observed patients who were found to have CA stones on post-operative stone analysis without positive stone cultures, positive pre-operative urine cultures, or a history of urinary tract infections (UTIs). The aim of our study is to characterize patients with CA stones, with and without evidence of infection, and examine their clinical outcomes. Methods: We retrospectively identified patients in our prospectively maintained stone database who had undergone surgical treatment for calculi containing CA on final stone analysis. SPSS was used to perform descriptive statistics and two-tailed T tests (p < 0.05). Results: We identified 53 patients with CA stones from our database. Most patients were female (n=35, 66.0%) and had undergone percutaneous nephrolithomy (PCNL) (n=44, 83.0%). Mean follow-up was 13.8 months. Almost all patients with CA stones had a documented vitamin D deficiency (n=47, 88.7%) and were prescribed vitamin D supplementation (n=46, 86.8%). Patients had a mean pre-operative stone burden of 2.8 cm (range 0.5-20cm) and over half of the patients had a positive pre-operative urine culture, post-operative stone culture, or history of UTIs (n=28, 52.8%). Patients with evidence of infection (infection stones) were more likely to have a GU anatomical abnormality (39% vs 4%, p<0.002), greater proportion of CA on stone analysis (51% vs 32%, p=0.037), hypocitraturia on 24-hour urine collection (85% vs 50%, p=0.06), and lower rates of freedom from next stone procedure (82% vs 96%, p=0.12). Patients with infection CA stones did not have longer lengths of stay, worse stone free rates, greater rates of ER presentations, or re-admission rates (all p>0.05) compared to patients without evidence of infection. Conclusions: Patients with CA stones have a high prevalence of vitamin D deficiency and prescribed vitamin D replacement. Patients with CA stones and evidence of infection tend to have higher proportions of CA on stone analysis, greater rates of hypocitraturia on 24-hour urine collections, and may have lower rates of freedom from subsequent stone treatment compared to patients without evidence of infection. SOURCE OF Funding: None
