Clinical use of cystine supersaturation measurements
Y Nakagawa, JR ASPLIN, DS GOLDFARB… - The Journal of …, 2000 - auajournals.org
The Journal of urology, 2000•auajournals.org
Purpose: We measured the concentration and solubility of cystine in urine from patients with
cystinuria or calcium stones and from normal subjects to determine whether urine cystine
supersaturation can be calculated from a standard nomogram of solubility versus pH or
needs to be measured directly. We also evaluated whether increasing pH of the 24-hour
collection recovered enough crystallized cystine to increase cystine supersaturation.
Materials and Methods: Cystine concentration, pH and usual stone risk factors were …
cystinuria or calcium stones and from normal subjects to determine whether urine cystine
supersaturation can be calculated from a standard nomogram of solubility versus pH or
needs to be measured directly. We also evaluated whether increasing pH of the 24-hour
collection recovered enough crystallized cystine to increase cystine supersaturation.
Materials and Methods: Cystine concentration, pH and usual stone risk factors were …
Purpose
We measured the concentration and solubility of cystine in urine from patients with cystinuria or calcium stones and from normal subjects to determine whether urine cystine supersaturation can be calculated from a standard nomogram of solubility versus pH or needs to be measured directly. We also evaluated whether increasing pH of the 24-hour collection recovered enough crystallized cystine to increase cystine supersaturation.
Materials and Methods
Cystine concentration, pH and usual stone risk factors were measured on 50 ml. aliquots of 24-hour collections from 24 patients with cystinuria, 22 calcium stone formers and 15 normal subjects. After 48 hours of incubation with sodium bicarbonate, a second aliquot was taken from the 24-hour collection for cystine concentration. The original urine at its ambient pH was incubated with an excess of cystine crystals for 24, 48, 72 or 96 hours at 37C to determine solubility and kinetics of equilibration.
Results
Cystine solubility varied so widely at any pH range that no predictive nomogram could be relied on for calculating supersaturation. Addition of sodium bicarbonate to the 24-hour urine significantly increased cystine concentration. Urine from stone formers had higher cystine solubility than urine from normal subjects.
Conclusions
Clinical management of cystinuria can be improved by direct measurement of cystine solubility because it varies widely at any given pH. Increasing 24-hour collection pH with sodium bicarbonate additionally improves accuracy of supersaturation measurement by recovering crystallized cystine.
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