Cystine analyses of separate day and night urine as a basis for the management of patients with homozygous cystinuria

Based on previous observations of the diurnal variation of urinary cystine excretion, the use of separate day and night urine collections was proposed . To improve the medical treatment of patients with cystinuria, this strate gy was performed to guide the fluid intake and the administration of SH com pounds (tiopronin, D-penicillamine,and MESNA). Twenty-six patients (19 trea ted with SH compounds and seven with alkalinization and hydration only) wer e followed during two 3.5-year periods. During Period 1, 24-h urine was col lected and during Period 2, separate day and night urine was collected. The re were 56 episodes of high urinary cystine supersaturation (>1,200 mu mol/ l) during Period 2, 47% of which would have evaded detection with 24-h urin e analysis. In comparison with Period 1, the urinary cystine concentration was lower (P < 0.05), and the urinary volume was higher (P < 0.05) during P eriod 2. Patients treated with tiopronin had reduced cystine excretion (P < 0.05) and at the end of Period 2, an increased dose of tiopronin, reflecti ng a more aggressive treatment. Furthermore, a reduced number of stone epis odes and need of active stone removal (P < 0.05) was noted in the whole gro up of patients. Analyses of separate day and night urine samples can be use d advantageously to reveal episodes of high supersaturation with cystine no t detected in 24-h urine samples. Such a procedure might be useful for opti mizing the treatment of patients with cystinuria.