Proportional reduction of urine supersaturation during nephrolithiasis treatment.
OBJECTIVE
During metabolic stone therapy, urine supersaturation decreases in proportion to pretreatment levels. We gauge the quantitative contribution of regression to the mean for reducing urine supersaturation from high pretreatment to lower values during therapy.


METHODS
The 24-hour urine supersaturations for calcium oxalate, calcium phosphate and uric acid were measured on 2 pretreatment and at least 1 treatment 24-hour collection for each of the 2,667 patients in 2 networks and at a university based specialty clinic. Changes in supersaturation between the first and second pretreatment collections were an estimate of random change and compared to therapeutic changes.


RESULTS
Supersaturations decreased between the first and second pretreatment collections, proportional to the supersaturation in the first collection. However, the magnitude of this effect was minor compared to therapeutic changes. Also, mean change between pretreatment collections was 0, whereas mean change with therapy was greater than 0 for all 3 supersaturations.


CONCLUSIONS
Although regression to the mean can be detected, it cannot be responsible for the decrease in urine supersaturation with therapy or the fact that the decrease is proportional to pretreatment mean supersaturation. The mechanisms responsible for proportional reduction remain to be clarified.
Coe
F L
FL
Nephrology Section, University of Chicago, Chicago, Illinois, USA.
Wise
H
H
Parks
J H
JH
Asplin
J R
JR
D002129:Calcium Oxalate / Q000652:urine*; D002130:Calcium Phosphates / Q000652:urine*; D006801:Humans; D012008:Recurrence; D014527:Uric Acid / Q000652:urine*; D014545:Urinary Calculi / Q000628:therapy / Q000652:urine*
D002130:Calcium Phosphates; C485828:alpha-tricalcium phosphate; C485830:tetracalcium phosphate; D002129:Calcium Oxalate; D014527:Uric Acid; C485838:calcium phosphate, monobasic, anhydrous; C020243:calcium phosphate; C485829:calcium phosphate, dibasic, anhydrous