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Differences in the free Ca 2+ in undiluted urine from stone formers and normal subjects using a new generation of ion‐selective electrodes
Author(s) -
Langley S.E.M.,
Fry C.H.
Publication year - 1995
Publication title -
british journal of urology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.773
H-Index - 148
eISSN - 1464-410X
pISSN - 0007-1331
DOI - 10.1111/j.1464-410x.1995.tb07339.x
Subject(s) - urine , chemistry , urinary system , electrode , ion , upper urinary tract , analytical chemistry (journal) , chromatography , urology , medicine , biochemistry , organic chemistry
Objectives To measure the ionized Ca 2+ in urine from normal subjects and patients with urinary tract stones. Patients and methods Urine samples were obtained from 37 normal subjects and 52 stone‐formers. Ca 2+ was measured using plastic dip‐cast ion‐selective electrodes; total Ca and other variables were measured by standard analytical techniques. Results The ionized Ca 2+ and the total Ca were greater in stone‐formers' urine although the difference was more significant with the Ca 2+ data, especially at a standardized pH. Absolute values of the Ca 2+ were dependent on the type of reference electrode used. The Ca 2+ was a function of urine pH; lower values were recorded as pH increased. Measured values of the Ca 2+ did not correlate well with calculated values using a standard computer program. Conclusions Measurement of the Ca 2+ in spot urine samples at a standard pH provides a more discriminative test than total Ca for the presence of urinary tract stones. The pH dependence of the Ca 2+ may have important consequences in the formation of urinary tract stones. The poor correlation between measured and computed values of Ca 2+ emphasizes the importance of accurate measurement of this variable.