Abstract: TH-PO1078

Determinants of Urine Chemistry in the Rare Kidney Stone Consortium (RKSC) Cystinuria Registry

Session Information

Category: Mineral Disease

  • 1204 Mineral Disease: Nephrolithiasis

Authors

  • Modersitzki, Frank, New York University School of Medicine, New York, Alabama, United States
  • Goldfarb, David S., New York Harbor VAMC, New York, New York, United States
Background

Urine chemistry is a determinant of stone formation in cystinuria. We previously showed that positive cystine capacity (CysCap), a measure of higher cystine solubility, led to fewer stone events. We queried the RKSC Cystinuria Registry to determine urinary and medication variables associated with positive (CysCap+), rather than negative (CysCap-) values.

Methods

This is the 1st report from the Cystinuria Registry, with data on 300 people with cystinuria (142 males, 158 females; age at enrollment 38 + 17 years). 112 participants had 306 determinations of CysCap, measured by Litholink (Chicago, IL). In this cross-sectional study we compared variables associated with CysCap+ vs CysCap-.

Results

Lower urine Na (r=0.48; Fig 1A) and creatinine (r=0.62, not shown) were associated with lower 24h urine cystine (UC; P<0.001). Increasing CysCap values were seen with increasing urine pH (rs=0.45, Fig 1B), volume (rs=0.44) and decreasing UC (rs=-0.44 Fig 1C; all P<0.001). Dividing Cyscap determinations into CysCap+ and CysCap- groups (Table), only higher urine volume and greater daily citrate doses were different. Relatively few participants were taking citrate or tiopronin.

Conclusion

Higher urine pH and volume and lower UC were associated with less lithogenic urine; lower UC was seen with less Na and creatinine. Higher volume and citrate doses distinguished patients with less lithogenic urine. Many patients with cystinuria may be undertreated and would benefit from better dietary adherence.

24h Urine Chemistry and Medications for CysCap- vs CysCap+
Values are mean (± SD)CysCap-CysCap+
24h Urine Volume (L); n:102,2052.5 (0.9)3.8 (1.6) P<0.001
Urine pH; n:100,1996.96 (0.33)7.18 (0.36)
24h Urine Sodium (meq); n:93,193195.8 (79.4)191.3 (101.0)
24h Urine Cystine (mg); n:101,2061078.3 (324.7)824.0 (269.9)
24h Urine Creatinine (mg); n:95,2041700.8 (656.6)1620.4 (683.1)
Citrate dose (meq/day); n:28,6142.3 (22.4)69.3 (32.9) P<0.05
Tiopronin dose (mg/day); n:22,41963.6 (410.0)1026.8 (502.5)

n was variable due to incomplete data

See results for figure legend

Funding

  • NIDDK Support