Collection under paraffin is not necessary for stability of urine pH over 24 h

Collection of urine under paraffin is routinely used in clinical practice for urine pH evaluation. To examine whether the accuracy of pH measurement is adversely influenced by the method of collection and storage, we divided each urine specimen and sent one aliquot to the laboratory under paraffin and another in a sealed 5-ml plastic syringe. In another experiment we evaluated the stability of urine pH measurement in a clinical setting. Urine collected under paraffin was tested immediately for pH; an aliquot from the same specimen was stored in a capped 5-ml syringe at 4 degrees C and tested after 24 h. We found no appreciable difference in measured pH between samples sent to the laboratory under paraffin or in a capped plastic syringe.