Does the Exposure of Urine Samples to Air Affect Diagnostic Tests for Urine Acidification?
- Title
- Does the Exposure of Urine Samples to Air Affect Diagnostic Tests for Urine Acidification?
- Author
- 김호중
- Keywords
- RENAL TUBULAR-ACIDOSIS; PH; COLLECTION; STABILITY; PCO2
- Issue Date
- 2012-08
- Publisher
- American Society of Nephrology
- Citation
- Clinical Journal of the American Society of Nephrology, Aug 2012, 7(8), P.1211-1216, 6P.
- Abstract
- Background and objectives For accurate measurement of pH, urine collection under oil to limit the escape of CO2 on air exposure is recommended. This study aims to test the hypothesis that urine collection under oil is not necessary in acidic urine in which bicarbonate and CO2 are minor buffers, because loss of CO2 would have little effect on its pH. Design, setting, participants, & measurements One hundred consecutive random urine samples were collected under oil and analyzed for pH, pCO2, and HCO3- immediately and after 5 minutes of vigorous shaking in uncovered flasks to allow CO2 escape. Results The pH values in 97 unshaken samples ranged from 5.03 to 6.83. With shaking, urine pCO2 decreased by 76%, whereas urine HCO3- decreased by 60%. Meanwhile, urine baseline median pH (interquartile range) of 5.84 (5.44-6.25) increased to 5.93 (5.50-6.54) after shaking (ΔpH=0.12 [0.07-0.29], P<0.001). ΔpH with pH≤6.0 was significantly lower than the ΔpH with pH>6.0 (0.08 [0.05-0.12] versus 0.36 [0.23-0.51], P<0.001). Overall, the lower the baseline pH, the smaller the ΔpH. Conclusions The calculation of buffer reactions in a hypothetical acidic urine predicted a negligible effect on urine pH on loss of CO2 by air exposure, which was empirically proven by the experimental study. Therefore, exposure of urine to air does not substantially alter the results of diagnostic tests for urine acidification, and urine collection under oil is not necessary.
- URI
- http://cjasn.asnjournals.org/content/7/8/1211http://hdl.handle.net/20.500.11754/48332
- ISSN
- 1555-9041; 1555-905X
- DOI
- 10.2215/CJN.03230312
- Appears in Collections:
- COLLEGE OF MEDICINE[S](의과대학) > MEDICINE(의학과) > Articles
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