Aims Hypercalciuria is a common poorly understood abnormality among stone formers. We aimed to identify hypercalciuric male stone formers with a primary defect in renal calcium reabsorption and to look for associated risk factors.
Methods A retrospective cross-sectional database study of 623 male idiopathic calcium stone formers with normal plasma ultrafilterable calcium levels attending the Southampton stone clinic. Filtered calcium was estimated from plasma ultrafilterable calcium (60% of total plasma calcium) and 24 h creatinine clearance. Reabsorbed calcium was the difference between filtered and excreted calcium.
Results 276 men had hypercalciuria (urine calcium >7.50 mmol/24 h); 347 had normocalciuria. Hypercalciuric men filtered more calcium than normocalciuric men: median values 247 and 227 mmol/24 h, but the ranges overlapped (175–371 and 153–316 mmol/24 h). However, across the entire filtration range, hypercalciuric men reabsorbed less of the filtered calcium. Among the hypercalciuric men, we noticed differences between those with high and low filtration. We therefore compared data for hypercalciuric men in the highest and lowest filtration quintiles (n=55). Men with high filtration were younger at their first stone episode and had significantly higher plasma ultrafilterable calcium and calcium reabsorption, urinary calcium, oxalate, urate and creatinine excretion and creatinine clearance. 35% with high filtration and 40% with low filtration had recurrent stones; 27% and 20%, respectively, had an affected first-degree relative.
Conclusions Hypercalciuric men reabsorbed proportionately less filtered calcium than normocalciuric men. Among hypercalciuric men, the risks for stones were higher in those with a high than a low filtered calcium load and presentation was earlier.