Abstract: TH-PO1083

Lower Than Normal Urine pH in Calcium Oxalate (CaOx) Stone Forming (SF) Women Is Due to Reduced Gastrointestinal (GI) Alkali Absorption

Session Information

Category: Mineral Disease

  • 1204 Mineral Disease: Nephrolithiasis


  • Bergsland, Kristin J., University of Chicago, Chicago, Illinois, United States
  • Coe, Fredric L., University of Chicago, Chicago, Illinois, United States
  • Worcester, Elaine M., University of Chicago, Chicago, Illinois, United States

We have previously found that in normal (N) men (M) and women (W) fed identical diets in a General Clinical Research Center (GCRC), the urine pH (UpH) of W exceeds that of M due to greater absorption of alkali from the GI tract. Since calcium (Ca) SF is often accompanied by altered UpH that reduces the solubility of SF salts in urine, we have similarly studied idiopathic hypercalciuric CaOx and CaP stone formers in the GCRC to identify whether differences in UpH regulation are associated with stone type within sex and if so, what components of acid-base metabolism are responsible for the differences.


We measured UpH and determinants of acid-base regulation in 25 N (13 M), 17 CaOx SF (11 M) and 15 CaP SF (8 M). We collected 15 urines and 20 blood samples over a 15 hour day in the GCRC; diet was fixed. GI anion excretion (GIAE) = [(Na + K + Ca+ Mg) - (Cl + P)] in urine (mEq/hr).


W CaOx SF had lower UpH than other W during the fed period (Table). Lower UpH in CaOx W was accompanied by higher net acid excretion (NAE) and urine titratable acid (TA), and reduced urine CO2 excretion and GIAE. In M CaP SF, GIAE was higher vs M N. Sulfate excretion (Sul) was reduced in all SF vs N.


The pathophysiology of Ca stone formation differs by sex. In the presence of hypercalciuria, normally high GIAE and UpH of W predisposes to CaP SF while higher TA and NAE and lower UpH in M favors CaOx SF. Exceptions are M CaP, with increased GIAE that correlates with a trend to higher UpH, and W CaOx, with lower than normal GIAE and higher NAE which translates into reduced urine CO2 and lower UpH. These differences may have clinical implications for use of stone therapies that affect UpH.

ANOVA by Sex and Subject Type
UpH6.49 ± 0.056.12 ± 0.07*6.58 ± 0.066.19 ± 0.05#6.29 ± 0.056.39 ± 0.06
U CO21.19 ± 0.090.49 ± 0.13*1.10 ± 0.120.89 ± 0.090.68 ± 0.101.14 ± 0.11†
U TA0.42 ± 0.030.59 ± 0.04*0.34 ± 0.040.64 ± 0.03#0.61 ± 0.030.56 ± 0.04#
U NH41.07 ± 0.051.18 ± 0.070.97 ± 0.061.21 ± 0.051.17 ± 0.051.26 ± 0.06#
U NAE0.30 ± 0.131.29 ± 0.18*0.22 ± 0.170.96 ± 0.13#1.10 ± 0.140.68 ± 0.16
U SUL1.64 ± 0.05*1.36 ± 0.071.22 ± 0.071.77 ± 0.05*1.55 ± 0.061.56 ± 0.06#
GIAE3.11 ± 0.181.50 ± 0.25*2.95 ± 0.231.87 ± 0.17#1.99 ± 0.192.77 ± 0.22$

Mean ± SE. *p<0.01 vs other subject types, same sex; #p<0.05 vs WOMEN, same subject type; †p<0.05 vs CAOX, same sex; $p<0.05 vs NONE, same sex. Excretions are in mmol/hr and adjusted for body surface area.


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