Publication: Characterizations of urinary sediments precipitated after freezing and their effects on urinary protein and chemical analyses
3
Issued Date
2009-06-01
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ISSN
15221466
03636127
03636127
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2-s2.0-66449122167
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Mahidol University
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SCOPUS
Bibliographic Citation
American Journal of Physiology - Renal Physiology. Vol.296, No.6 (2009)
Suggested Citation
Putita Saetun, Tistaya Semangoen, Visith Thongboonkerd Characterizations of urinary sediments precipitated after freezing and their effects on urinary protein and chemical analyses. American Journal of Physiology - Renal Physiology. Vol.296, No.6 (2009). doi:10.1152/ajprenal.90736.2008 Retrieved from: https://repository.li.mahidol.ac.th/handle/123456789/27207
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Title
Characterizations of urinary sediments precipitated after freezing and their effects on urinary protein and chemical analyses
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Abstract
One of the obstacles in analyzing frozen urine samples is the formation of uncharacterized precipitates. Frequently, these precipitates are discarded before analysis. Some laboratory data may be erroneous if these precipitates contain important compounds. In the present study, we examined urinary sediments precipitated after overnight storage at -20°C. Although cells and debris were removed before freezing, the precipitates remained, whereas storing the centrifuged urine overnight at 4°C did not result in precipitate formation. There were no significant differences observed among 10 healthy individuals (5 men and 5 women). EDTA (5 mM) could efficiently reduce the amount of precipitates to ∼25% of the initial amount. The addition of exogenous CaCl2, but not sodium oxalate and NaCl, significantly increased the amount of precipitates in a dose-dependent manner. Linear regression analysis revealed a significant correlation between endogenous urinary calcium level and the amount of precipitates (r = 0.894; P < 0.001). Urine pH also had some effects on the type and amount of precipitates. These precipitates were composed mainly of calcium oxalate dihydrate and amorphous calcium crystals. The results also showed that these precipitates could deplete urinary proteins and calcium ions (23.6 ± 1.1% decrease). Therefore, these freezer-induced urinary sediments significantly affect protein analysis and measurement of calcium levels in the urine. However, vigorous shaking of the sample at room temperature could redissolve these precipitates. Our data strongly indicate that these freezer-induced precipitates must be taken into account when the frozen urine samples are analyzed. Copyright © 2009 the American Physiological Society.