Abstract: SA-PO683
Independent Effects of Age and Kidney Function on Urine pH in Stone Forming Patients
Session Information
- Bone and Mineral Metabolism: Clinical - II
October 27, 2018 | Location: Exhibit Hall, San Diego Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Bone and Mineral Metabolism
- 402 Bone and Mineral Metabolism: Clinical
Authors
- Menezes, Cameron J., University of Chicago, Chicago, Illinois, United States
- Asplin, John R., Litholink Corp, Chicago, Illinois, United States
- Worcester, Elaine M., University of Chicago, Chicago, Illinois, United States
- Coe, Fredric L., University of Chicago, Chicago, Illinois, United States
Background
We have found that normal women (W) have higher urine pH (UpH) than men (M) fed identical diets in a clinical research center. Prevalence of high UpH-dependent phosphate stones decreases with age while that of uric acid stones – signifying low UpH - increases. We sought to determine if UpH falls with age in a large population of stone formers (SF), and if so to quantify the independent effects of sex, falling renal function, and age itself.
Methods
From a large dataset of 12839 SF patients with pretreatment 24 hour urine collections and matching serum collections (Litholink) we selected 7891 (3605 F) SF without markers of systemic disease, infections, or missing lab values. The final dataset was used to model UpH using continuous generalized linear models with urine potential renal acid load (uPRAL) calculated from urine charge balance, age, creatinine clearance (CCr) and their appropriate cross products. To directly compare the effect sizes of CCr and age, we treated both as categorical variables in a separate analysis.
Results
UpH in W was higher than M at all ages and UpH declines with age and CCr via separable effects. uPRAL, age, and CCr are all significant (p<.01) predictors of UpH (Table), and the effect of uPRAL is conditioned by both CCr and age. The observed sex difference is fully accounted for after adjustment in both the continuous and categorical models of UpH.
Conclusion
Age and CCr exert separate effects on UpH in SF patients. Of the two, age is the more important predictor with an effect size approximately twice that of CCr. UpH is most strongly conditioned by uPRAL with effects that are mediated by age and kidney function.
| CONTINUOUS | CATEGORICAL (CCR+AGE) | |||
| Fisher's F | EFFECT | Fisher's F | EFFECT | |
| CONSTANT | --- | 6.50 | --- | 6.17 |
| uPRAL | 5960 | -0.15 | 6376 | -0.16 |
| AGE | 764 | -0.08 | 87.7 | -0.24±0.01 # |
| CCR | 21 | 0.005 | 17.4 | 0.11±0.01 # |
| SEX | 5.2* | M=0.034 | 2.0** | M=-0.0063 |
| SEX*uPRAL | 21 | M=0.01 | 15.3 | M=0.005 |
| AGE*uPRAL | --- | ----- | 12.0 | H=-0.12; L=-0.17 + |
| CCR*uPRAL | --- | ----- | 18.8 | H=-0.13; L=-0.19 |
| SEX*AGE | 8 | M=-0.01 | 2.4* | ----- |
| MULTIPLE R^2 | 0.463 | --- | 0.484 | |
| All effects have significance p<.01 unless marked. All effects per 10 unit change unless marked. #, Coefficient and SE of linear contrast across hexiles. *, p <.05. **, P= NS, forced in for cross products. +, largest effects not in order, interval describes the range of effects only. All models fully adjust sex difference. | ||||
Funding
- NIDDK Support