Are preservatives necessary in 24-hour urine measurements?

Yilmaz G., Yilmaz F. M. , Hakligör A., YÜCEL D.

Clinical Biochemistry, vol.41, no.10-11, pp.899-901, 2008 (Journal Indexed in SCI Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 41 Issue: 10-11
  • Publication Date: 2008
  • Doi Number: 10.1016/j.clinbiochem.2008.03.002
  • Title of Journal : Clinical Biochemistry
  • Page Numbers: pp.899-901
  • Keywords: Calcium, Magnesium, Phosphate, Preservative, Uric acid, Urine collection


Background: 24-h urine measurements are used in the routine diagnosis and follow-up of many diseases in the clinical laboratory. Calcium (Ca2+), magnesium (Mg2+), phosphate (PO43-) and uric acid are frequently requested markers in 24-h urine samples. Because of the different solubilities of these parameters, different urine collection conditions - urine in base for uric acid and urine in acid for Ca2+, PO43- and Mg2+ measurements - are recommended. Methods: We aimed to test the effect of addition of preservatives and heating of the urine specimen on the results obtained for Ca2+, Mg2+, PO43- and uric acid by comparison with untreated samples results. Spot (n = 20) and 24-h urine (n = 50) samples were obtained from patients for routine urine analysis. A single spot urine sample was divided into five aliquots of 10 mL each: one containing 200 μL of HCl (6 N), another containing 200 μL of sodium bicarbonate, NaHCO3 (5 g/L), two others in which the same preservative agents were added 24 h after the collection, and one without any preservative (untreated). Ca2+, PO43-, uric acid and Mg2+ were measured in triplicate and at three different time points during the study: at the time of sampling (0 h), 24 h after sampling, and after heating the samples. The 24-h urine samples were collected without preservatives and analytes were measured promptly before and after acidification/alkalinization. Results: There was no statistically significant difference between untreated and treated samples (p > 0.05). Heating also failed to show any difference in the results (p > 0.05). Conclusion: According to our results, addition of preservatives is not necessary for measurement of Ca2+, Mg2+, PO43- and uric acid in promptly assayed 24-h urine samples. © 2008 The Canadian Society of Clinical Chemists.