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Acidification and urine calcium: is it a preanalytical necessity?
R Sodi1, L B Bailey, J Glaysher
1Department of Clinical Biochemistry & Metabolic Medicine, Royal Liverpool & Broadgreen University Hospital, UK. ravsodi@yahoo.com
Annals of Clinical Biochemistry
|September 5, 2009
Summary
Acidification of urine samples is not necessary for accurate calcium measurement. This study found no significant difference in urine calcium levels between acidified and non-acidified samples, simplifying sample collection.
Area of Science:
- Clinical Chemistry
- Urology
- Laboratory Medicine
Background:
- Accurate urine calcium measurement traditionally requires sample acidification.
- Acidification presents safety risks for patients and laboratory personnel.
- The necessity of preanalytical acidification for urine calcium analysis requires re-evaluation.
Purpose of the Study:
- To determine if urine sample acidification is a mandatory preanalytical step for accurate calcium measurement.
- To assess the impact of varying hydrochloric acid concentrations on urine calcium stability.
- To compare urine calcium levels in acidified versus non-acidified samples.
Main Methods:
- Collected 24-hour urine samples from 133 patients without acid.
- Tested the effect of hydrochloric acid (HCl) on urine calcium in aliquots.
- Measured calcium immediately, after 12 hours, and after 7 days of storage at 4°C.
- Compared paired acidified and non-acidified samples from 133 patients.
- Utilized cresolphthalein complexone colorimetric assay.
Main Results:
- No significant difference in urine calcium concentration was observed between acidified and non-acidified samples (P = 0.888).
- Varying concentrations of HCl did not significantly alter urine calcium levels compared to non-acidified samples (P = 0.987).
- No correlation was found between basal urine pH and urine calcium levels at any time point.
Conclusions:
- Urine sample acidification is not a preanalytical necessity for accurate urine calcium measurement.
- Eliminating acidification simplifies sample collection and reduces associated risks.
- This finding has implications for routine laboratory practices in urine analysis.
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