HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 296/6/F1346    most recent 90736.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Saetun, P. Articles by Thongboonkerd, V. PubMed PubMed Citation Articles by Saetun, P. Articles by Thongboonkerd, V.

Characterizations of urinary sediments precipitated after freezing and their effects on urinary protein and chemical analyses

¹Medical Proteomics Unit, Office for Research and Development, and ²Department of Immunology and Immunology Graduate Program, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand

Submitted 10 December 2008 ; accepted in final form 26 March 2009

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.

calcium; crystal; oxalate; precipitate; protein; urine; urinalysis