Bonn Risk Index based micromethod for assessing risk of urinary calcium oxalate stone formation

The Bonn Risk Index has been used to evaluate the risk of urinary calcium oxalate stone formation. According to the original method, risk should be determined based on a 200 ml urine sample taken from a 24-hour collection. We evaluated whether the Bonn Risk Index can also be effectively determined in small urine samples.

We studied 190 children and adolescents with nocturia and calcium oxalate urolithiasis. Initially Bonn Risk Index was determined according to the original method of Laube. Subsequently Bonn Risk Index was calculated using a computer program controlling a specially designed system to define the time point of induced crystallization based on consecutive urine samples of 1.5, 2.0 and 3.0 ml.

No significant differences were found in Bonn Risk Index between values obtained from 200 ml samples and those based on the micromethod with urine samples of 2 and 3 ml.

Assessment of risk of urinary calcium oxalate stone formation with Bonn Risk Index in small urine volumes, based on prototype equipment controlled by specialized computer software, is comparable to the original method. This finding facilitates the procedure and improves Bonn Risk Index determination in children.