[Calcium-dependent calcium oxalate lithiasis (type IIa). The importance of urinary citrate and the calcium/citrate ratio]. / Lithiase oxalo-calcique de structure calcium dépendante (type IIa). Intérêt de la citraturie et du rapport calcium/citrate.

BACKGROUND: Type IIa urinary lithiasis (calcium oxalate dihydrate, weddellite) has a calcium-dependent structure implicating hyper-calciuria for its formation. CASE REPORT: We observed a case of type IIa lithiasis in a patient without elevated urine calcium. Weddellite crystals with a hexagonal habit were found in the nocturnal urines. The only urinalysis anomaly was a low citrate level giving a calcium/citrate level > 3. Oral potassium citrate normalized urinary citrate and the calcium/citrate ratio. After 3 years follow-up, crystal formation has remained negative. DISCUSSION: As illustrated by this case, the calcium/citrate ratio, rather than total urine calcium, would be a good indicator of urinary calcium output and the potential risk for weddellite crystal formation in the presence of oxalates.

[Calcium oxalate lithiasis. Relationship between biochemical risk factors and crystalline phase of the stone]. / Lithiase oxalocalcique. Relation entre facteurs de risque biochimiques et phase cristalline du calcul.

OBJECTIVES: To identify biochemical risk factors specific to each crystalline phase of calcium oxalate (calcium oxalate monohydrate and calcium oxalate dihydrate) in order to allow more specific medical management of calcium oxalate stones and better prevention of recurrences. MATERIAL AND METHODS: The authors compared the urine biochemistry (morning and 24-hour) of 19 patients with stones containing more than 95% of calcium oxalate monohydrate with those of 16 patients with stones containing more than 60% of calcium oxalate dihydrate (calcium phosphate < 12%). RESULTS: Urinary calcium, expressed as excretion rate and as concentration, and the calcium/citrate ratio were significantly higher in the calcium oxalate dihydrate group than in the calcium oxalate monohydrate group: (9.2 +/- 3.8 mmol/24 h versus 4.4 +/- 1.7 mmol/24 h); (4.9 +/- 2.1 mmol/l versus 2.4 +/- 1.1 mmol/l); (3.3 +/- 1.6 versus 1.6 +/- 0.7). The mean pH of the morning urine was lower in the calcium oxalate monohydrate group, just below the cut-off value of 5.5. CONCLUSION: There is a strong correlation between predominantly calcium oxalate dihydrate stones and hypercalciuria or calcium/citrate ratio > 3. The close relationship between urine biochemistry and crystalline phases of calcium oxalate confirms the clinical value of morphoconstitutional analysis of urinary stones. Identification of risk factors, based on stone analysis, allows more specific medical management of the stones and, in the longer term, better prevention of recurrences.