BAUS 2015

Introduction: Despite advances in genotyping, the phenotype of cystinuria remains difficult to predict, risking under/over treatment. Urinary cystine levels do not provide sufficient prediction of disease severity. We studied whether presence/absence of urinary cystine crystals and urinary cystine levels could determine disease severity.
Methods: 30 adult cystinuric patients with >5 years follow up were categorised into three different severity groups(least to most respectively),10 patients in each group; A-recurrent stone formers(no interventional treatment), B-previous URS, C-previous PCNL. Each group was subdivided into 2 categories depending on presence/absence of cystine crystals. Urinary cystine levels for each patient visit were recorded.
Results: male:female patients were equal. Overall average age of patients was 45(range 21-73 years). Median age tended to decrease as disease severity increased Group A-49yrs(age range 26-73), Group B-45yrs(29-65), Group C-35yrs(21-63). 11/30 (36.6%) patients had cystine crystals, almost half 5/11(45.5%) were most severe group. Positive correlation between disease severity, presence of crystals(A=2/10, B=4/10), C=5/10) and concentration of urinary cystine(178.2 vs 204.4 vs 211.7 uM/mMC). Average level of urinary cystine for the crystals present group was statistically significantly higher 1488.0umol/L compared to crystals absent: 705.5umol/L(p<0.0001).
Conclusion: Our results suggest that there is potential for the combination of cystine crystalluria and urinary cystine levels as prognostic biomarkers for the severity of cystinuria. Further work is needed to evaluate if this combination of the presence of crystals and elevated urinary cystine levels will also be predictive of patients at risk of stone formation that may require invasive intervention.