Pure vs. mixed calcium oxalate nephrolithiasis: metabolic determinants and stratified management strategies

To investigate metabolic differences between pure and mixed calcium oxalate (CaOx) stone formers and identify key metabolic signatures for prevention strategies.

A retrospective analysis was conducted on 101 patients from a metabolic clinic database, identifying 49 (48.5%) as CaOx stone formers based on non-zero CaOx monohydrate or dihydrate percentages. Patients were stratified into 25 (51%) with pure CaOx stones and 24 (49%) with mixed stones (CaOx with secondary components). Metabolic parameters (urine volume, calcium, citrate, oxalate, uric acid, sodium, magnesium, serum calcium, uric acid, vitamin D, PTH, and urine pH) were analyzed and compared.

The 49 CaOx patients had a median age of 46 years (IQR 34.5-63), with 33 males (67.3%) and 16 females (32.7%). Surgical history included a median of 2 prior procedures (IQR 0-20), with 89.7% undergoing ureteroscopy. Pure CaOx patients showed higher hypercalciuria (60% vs. 29.2%, p = 0.04) and hypocitraturia (32% vs. 16.7%, p = 0.3), while mixed CaOx patients exhibited slightly lower hyperuricemia (20.8% vs. 24% in pure) and acidic urine pH < 5.5 (24% vs. 25%), reflecting uric acid stones in their composition. Low urine volume (< 2000 mL) was common (56% pure vs. 33.3% mixed). Other parameters (hyperoxaluria, hypomagnesuria, hypovitaminosis D) showed minimal differences.

Metabolic profiles differ between pure and mixed CaOx stones, with hypercalciuria and hypocitraturia in pure stones and hyperuricemia and low urine pH in mixed stones. Tailored prevention includes indapamide and citrate supplementation for pure CaOx and alkalinization for mixed stones, alongside universal hydration.