Login to Access Video or Poster Abstract: MP90-09
Sources of Funding: None.

Introduction

The metabolic syndrome plays an important role in lithogenesis of calcium oxalate stones, but to our knowledge no study has clinically correlated metabolic factors that influence stone subtype. It has been indicated that calcium oxalate monohydrate (COM) stones are more likely of tubular origin as secondary deposits onto calcium apatite whereas calcium oxalate dihydrate (COD) stones are more likely to form in solution. We sought to perform a comprehensive analysis of metabolic and clinical factors in patients who make predominantly one type of calcium oxalate stone.

Methods

From our prospectively maintained database of 1049 kidney stone formers between 01/2014 - 06/2016, we identified 95 patients with comprehensive medical records including stone analysis who had predominantly (≥80%) COM (75 pts) or COD (20 pts) composition. Another 27 patients had mixed COM and COD stones (<80% of one subtype). Clinical, demographic and laboratory parameters were compared between (>80%) COM or COD stones.

Results

There were no differences in age, gender or BMI between the COM and COD patients. COM patients were more likely to be hypertensive (46.7% vs. 15% p=0.01) and this difference was more pronounced in males (60% vs. 16.7%, p=0.007). Male COM patients were also more likely to be diabetic (22% vs. 0%, p=0.102). There were no differences in hyperlipidemia, coronary artery disease, gastrointestinal disease, and serum markers of uric acid, calcium, creatinine or HbA1c. COM patients were more likely to have hypocitraturia compared to COD patients (49.3% vs. 25%, p = 0.05). Male COM patients had significantly higher urinary oxalate levels (48 vs. 37 mg/d, p=0.05) compared to male COD formers. COD females showed a trend towards higher calcium levels vs. COM females (213 vs. 140 mg/d, p=0.13). The calcium/oxalate ratio in COD formers was significantly higher compared to COM formers (6.46 vs. 4.84, p < 0.05). No differences were observed for urine uric acid levels, supersaturation of uric acid, CaOx supersaturation, magnesium, and pH.

Conclusions

Our study suggests that HTN and DM, two components of the metabolic syndrome, are more closely linked to COM stones compared to COD stones. Patients with higher urine oxalate and lower urine citrate levels tend to form COM stones, while those with a higher urine calcium/oxalate ratio tend to form COD stones. This suggests that the two stone subtypes are clinically and metabolically different and thus may have different etiology.

Funding

None.