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 se rum phosphate may be an important indicator of nephrolithiasis risk. We det ermined 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 st one clinic followup were reviewed. Initial serum phosphate levels were comp ared with stone recurrence, complications due to stones, initial visit urin ary laboratory values and the medical diagnoses made during followup. Unpai red 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 (mea n age 52). Of the patients 50 were recurrent and 26 were single stone forme rs. Serum phosphate levels were lower in women than in men. No consistent a ssociations existed between initial or future serum phosphate levels and st one recurrence, complications from stones, urinary values or other medical diagnoses made during followup. Conclusions: Serum phosphate does not appear to be an independent risk fact or for urinary tract stone recurrence or complications, or a reliable early predictor of occult disease.