title: Decreases in albumin/creatinine and N-acetylglucosaminidase/creatinine ratios in urine samples stored at -20 degrees C.
abstract: The effects of storage for 6 months or 2 years at -20 degrees C were studied in urine samples from Type II diabetic patients by assaying albumin by immunoturbidity, N-acetylglucosaminidase (EC 3.2.1.30) by methoxynitrovinylphenol release, and creatinine by the Jaffé method. There were significant decreases (P < 0.001) in albumin/creatinine ratios from 1.14 (0.63-2.98) to 0.83 (0.32-2.12) g/mol (median + interquartile ranges) after 6 months (n = 97), and from 1.64 (0.74-5.72) to 1.00 (0.37-4.54) g/mol after 2 years (n = 89). The percentage of samples with results below the detection limit of the albumin assay (2 mg/L) increased from 5% to 21% after 6 months and from 0% to 34% after 2 years. N-Acetylglucosaminidase/creatinine ratios decreased (P < 0.001) from 520 (358-832) to 380 (263-695) U/mol after 6 months and from 520 (330-865) to 258 (82-462) U/mol after 2 years. The effect of storage was greater in samples with concentrations in the normal range (< 2.5 g/mol for albumin/creatinine, < 500 U/mol for N-acetylglucosaminidase/creatinine). Samples with albumin concentrations more than twice the normal range were still detected as abnormal after storage at -20 degrees C; e.g., 18% were > 5 g/mol (albumin/creatinine) initially, with 17% > 5 g/mol after 6 months of storage. We therefore recommend storage of urine samples at 4 degrees C for no longer than 7 days before assay.
authors.affiliation: Diabetes Research Laboratories, Radcliffe Infirmary, Oxford, UK.
authors.forename: S E
authors.initials: SE
authors.lastname: Manley
authors.forename: M E
authors.initials: ME
authors.lastname: Burton
authors.forename: K E
authors.initials: KE
authors.lastname: Fisher
authors.forename: C A
authors.initials: CA
authors.lastname: Cull
authors.forename: R C
authors.initials: RC
authors.lastname: Turner
mesh_terms: D000118:Acetylglucosaminidase / Q000652:urine*; D000419:Albuminuria / Q000652:urine*; D003404:Creatinine / Q000652:urine*; D003924:Diabetes Mellitus, Type 2 / Q000652:urine*; D004355:Drug Stability; D004795:Enzyme Stability; D005188:False Negative Reactions; D005615:Freezing; D006801:Humans; D011786:Quality Control; D012016:Reference Values; D013048:Specimen Handling / Q000379:methods*
chemical_list: D003404:Creatinine; D000118:Acetylglucosaminidase