Does hyperphosphaturia underlie hypercalciuria?

The diagnostic value of the phosphate levels in serum and 24-hour urine samples in patients with recurrent renal stone disease

OBJECTIVE

The aim of this study is to investigate the value of phosphate levels in serum and urine in patients with recurrent renal stone disease.

MATERIALS AND METHODS

The patients (n:60) were divided into two groups as first-time stone disease (group 1) and recurrent renal stone disease (group 2). The demographical datas and their historical information were recorded and physical examination was done. The sera and urine for 24 hr were obtained from patients to measure electrolyte levels especially phosphorus. In addition, based on presenting serum phosphate levels, patients were divided into the hypophosphatemia group, less than 2.5 mg/dl; normophosphatemia group, between 2.5-5.2 mg/dl; and hyperphosphatemia group greater than 5.2 mg/dl.

RESULTS

The mean age of study group was 45 (21-70) years. Thirty-six patients (60%) were in group 1 and 24 patients (40%) were in group 2. No statistically correlation was found between stone recurrence and phosphate levels both in serum and urine. There was only a statistical association of K levels in 24-hour urine samples between group 1 and 2.

CONCLUSION

There was no significant association between stone recurrence and initial phosphate levels in the serum or in urine. We do not propose to determine phosphate levels routinely in management of patients with stone disease.

Serum phosphate in stone formers: what does a low serum phosphate level mean?

PURPOSE

Metabolic evaluation is indicated in stone formers to identify and subsequently modify risk factors for nephrolithiasis. Some believe that serum phosphate may be an important indicator of nephrolithiasis risk. We determined whether serum phosphate is an independent risk factor for recurrent calcium stone formation and whether it may be used as an early marker for occult disease, such as hyperparathyroidism.

MATERIALS AND METHODS

The charts of all patients with regular long-term stone clinic followup were reviewed. Initial serum phosphate levels were compared with stone recurrence, complications due to stones, initial visit urinary laboratory values and the medical diagnoses made during followup. Unpaired 2-sample t tests, and correlation and logistic regression analyses were performed with statistical significance at p <0.05.

RESULTS

Data were available on 51 men and 25 women 22 to 74 years old (mean age 52). Of the patients 50 were recurrent and 26 were single stone formers. Serum phosphate levels were lower in women than in men. No consistent associations existed between initial or future serum phosphate levels and stone recurrence, complications from stones, urinary values or other medical diagnoses made during followup.

CONCLUSIONS

Serum phosphate does not appear to be an independent risk factor for urinary tract stone recurrence or complications, or a reliable early predictor of occult disease.