Alkalinization of urine samples preserves albumin concentrations during prolonged frozen storage in patients with diabetes mellitus

Diabet Med. 2009 May;26(5):556-9. doi: 10.1111/j.1464-5491.2009.02721.x.

Abstract

Background: In epidemiological studies in patients with diabetes, urine samples are often stored frozen prior to assessment of urinary albumin concentration (UAC). However, prolonged frozen storage may result in a falsely low UAC. In the current study, we investigated whether adjustment of urinary pH to alkaline values prior to frozen storage can prevent this problem.

Methods: Urine samples were collected in 90 patients from our diabetes outpatient clinic and divided into two portions. One portion was first adjusted to pH > 8.0 with 0.1 m sodium hydroxide, the other was left unprocessed. Both portions were divided into aliquots. UAC was assessed in fresh samples and after 7 days, 1, 6 and 12 months of storage at -20 and -80 degrees C.

Results: Until 1 month of storage there were no significant changes in UAC. After longer storage, UAC fell significantly in pH unadjusted samples stored at -20 degrees C, with a -7.6% (27.8) and -13.6% (31.7) change after 6 and 12 months storage, respectively. No significant change in UAC occurred in pH adjusted samples stored at -20 degrees C or when samples were stored at -80 degrees C, both with and without pH adjustment. Variation in UAC assessed after 12 months of storage was larger for samples stored at -20 degrees C without adjustment of pH than for the samples stored with pH adjustment or stored at -80 degrees C.

Conclusions: Urine alkalinization to pH > 8.0 prevents the decline in UAC associated with 12 months of frozen storage at -20 degrees C and results in lower variation between samples after storage.

Publication types

  • Evaluation Study

MeSH terms

  • Albuminuria*
  • Diabetes Mellitus / urine*
  • Freezing
  • Humans
  • Hydrogen-Ion Concentration*
  • Sodium Hydroxide
  • Specimen Handling / methods*
  • Time Factors

Substances

  • Sodium Hydroxide