title: Increased urinary IgG/albumin index in normoalbuminuric insulin-dependent diabetic patients: a laboratory artefact.
abstract: The previous observation that urinary IgG excretion is increased in normoalbuminuric insulin-dependent (IDDM) patients is unexplained and could possibly be related to a laboratory phenomenon. When untreated urine samples were stored -20 degrees C for 2 to 4 weeks, the IgG/albumin Index (IgG clearance divided by albumin clearance) was higher in normoalbuminuric IDDM patients than in control subjects (0.91 (0.68-1.54), n = 27 vs 0.72 (0.55-0.79), n = 15 (median (interquartile range)), p < 0.05). In normo- and microalbuminuric IDDM patients the IgG/albumin index was higher in urine samples with glucose than without glucose (1.16 (0.93-1.68), n = 11 vs 0.73 (0.50-0.91), n = 16, p < 0.05, and 0.33 (0.23-0.60), n = 17 vs 0.15 (0.10-0.26), n = 14, p < 0.02 for normo- and microalbuminuric patients, respectively). We, therefore, evaluated the preserving effects of glucose and bovine serum albumin (BSA) on urinary IgG after 1 h to 16 weeks of freezing at -20 degrees C in 4 non-diabetic subjects (proteinuria ranging from 0.05 to 8.0 g 24 h-1). Urine samples were either stored without precautions or treated with addition of phosphate buffer, BSA (1%) and glucose 100 and 300 mM). The weekly decline from 1 to 16 weeks of IgG in the urine aliquots diluted 1:1 with buffered glucose 300 mM and glucose 300 mM + BSA 1% was insignificant, whereas urinary IgG declined with all other storage regimes (p < 0.05). These results suggest that glucose in urinary specimens of IDDM patients prevents at least in part the loss of urinary IgG and may thus explain the higher urinary IgG/albumin index when unprocessed urine is stored frozen before assay. Laboratory precautions are necessary when urinary IgG cannot be measured immediately.
authors.affiliation: Department of Internal Medicine, Groningen State University Hospital, The Netherlands.
authors.forename: K
authors.initials: K
authors.lastname: Hoogenberg
authors.forename: P
authors.initials: P
authors.lastname: Visser
authors.forename: J
authors.initials: J
authors.lastname: Marrink
authors.forename: W J
authors.initials: WJ
authors.lastname: Sluiter
authors.forename: R P
authors.initials: RP
authors.lastname: Dullaart
mesh_terms: D000328:Adult; D000419:Albuminuria / Q000652:urine*; D000818:Animals; D016477:Artifacts; D002417:Cattle; D002624:Chemistry, Clinical / Q000379:methods*; D015331:Cohort Studies; D003922:Diabetes Mellitus, Type 1 / Q000503:physiopathology*; D005615:Freezing; D005947:Glucose / Q000737:chemistry*; D006029:Glycosuria / Q000652:urine; D006801:Humans; D007074:Immunoglobulin G / Q000737:chemistry / Q000652:urine*; D008875:Middle Aged; D012709:Serum Albumin / Q000737:chemistry; D013048:Specimen Handling; D013997:Time Factors
chemical_list: D007074:Immunoglobulin G; D012709:Serum Albumin; D005947:Glucose