Apparent Loss of Urinary Albumin during Long-term Frozen Storage: HPLC vs Immunonephelometry

Abstract

Background: Urinary albumin detection by immunonephelometry is decreased by ϳ30% in samples that have been frozen at ؊20°C. An HPLC method for assessment of urinary albumin that detects immunoreactive and immunochemically nonreactive albumin has been introduced as an alternative to immunonephelometry. We investigated whether this technique is affected by sample temperature, particularly freezing. Methods: Urine samples (n ‫؍‬ 295) were collected from the general population (Prevention of Renal and Vascular End-Stage Disease Study). Samples were assessed by both immunonephelometry and HPLC when fresh and after storage at ؊20°C for 4, 8, and 12 months and at ؊80°C for 12 months. Results: With immunonephelometry, storage for 4, 8, and 12 months at ؊20°C resulted in mean (SD) urine albumin changes of ؊21% (29%), ؊28% (29%), and ؊34% (31) (P <0.001 for trend). Storage at ؊80°C resulted in a 5% (19%) change after 12 months of storage (not significant). With HPLC, storage for 4, 8, and 12 months at ؊20°C resulted in urine albumin changes of ؊33% (28%), ؊43% (24%), and ؊55% (21%; P <0.001 vs immunonephelometry). Storage at ؊80°C resulted in a ؊29% (29%) change (P <0.001 vs immunonephelometry). Conclusion: Loss of albumin after freezing urine depends not only on freezing temperature but also on detection method. Detection of albumin by immuno-

Combining GFR and Albuminuria to Classify CKD Improves Prediction of ESRD

“…18 -21 In large populations (n Ͼ 1000) and with 20 databases imputed, as in our study, this technique has been shown to handle up to 90% missing values with a validity and precision of the imputed values almost identical to the "true" values. 22,23 To avoid potential artifacts, we measured ACR in three nonfrozen urine samples within 5 d. This is highly recommended 24,25 and could give more accurate results than a single measurement. Other limitations may be attributed to the imprecision of the Modification of Diet in Renal Disease (MDRD) formula in the range of near-normal values leading to risk category misclassification of some participants.…”

Effect of Sampling Method and Storage Conditions on Albumin, Retinol-Binding Protein, And N-Acetyl-β-D-Glucosaminidase Concentrations in Canine Urine Samples

“…4,11,16,17,26 To the authors' knowledge, the effect of sampling method on urinary marker concentrations has never been reported in dogs or cats. In reports on uALB, uRBP, or uNAG in canine or feline urine, cystocentesis as well as catheterization and midstream voided urine have been used.…”

Reactivity of Urinary Albumin (Microalbumin) Assays with Fragmented or Modified Albumin

“…Albumin degradation could result from either action of proteases or free radicals. Several reports offer varying views regarding the stability of urine specimens stored at Ϫ20°C (33)(34)(35)(36)(37). The recent report by Brinkman et al (37 ) notes a progressive decline in results by immunonephelometric assay for specimens stored at -20°C, but an even greater decline for results by sizeexclusion chromatography.…”

“…Several reports offer varying views regarding the stability of urine specimens stored at Ϫ20°C (33)(34)(35)(36)(37). The recent report by Brinkman et al (37 ) notes a progressive decline in results by immunonephelometric assay for specimens stored at -20°C, but an even greater decline for results by sizeexclusion chromatography. Those results suggest that the size-exclusion assay is more sensitive to structural changes of albumin during storage than is the immunonephelometric assay, countering a previous hypothesis that analysis by size exclusion is less sensitive to albumin degradation (15,16 ).…”