Current Issues in Measurement and Reporting of Urinary Albumin Excretion

Abstract

BACKGROUND: Urinary excretion of albumin indicates kidney damage and is recognized as a risk factor for progression of kidney disease and cardiovascular disease. The role of urinary albumin measurements has focused attention on the clinical need for accurate and clearly reported results. The National Kidney Disease Education Program and the IFCC convened a conference to assess the current state of preanalytical, analytical, and postanalytical issues affecting urine albumin measurements and to identify areas needing improvement. CONTENT:The chemistry of albumin in urine is incompletely understood. Current guidelines recommend the use of the albumin/creatinine ratio (ACR) as a surrogate for the error-prone collection of timed urine samples. Although ACR results are affected by patient preparation and time of day of sample collection, neither is standardized. Considerable intermethod differences have been reported for both albumin and creatinine measurement, but trueness is unknown because there are no reference measurement procedures for albumin and no reference materials for either analyte in urine. The recommended reference intervals for the ACR do not take into account the large intergroup differences in creatinine excretion (e.g., related to differences in age, sex, and ethnicity) nor the continuous increase in risk related to albumin excretion. DISCUSSION:Clinical needs have been identified for standardization of (a) urine collection methods, (b) urine albumin and creatinine measurements based on a complete reference system, (c) reporting of test results, and (d) reference intervals for the ACR.

A reference system for urinary albumin: current status

“…Other preanalytic and analytic factors that can also influence use of urinary albumin as a biomarker of renal disease and that may benefit from standardized approaches are summarized below based on the report from the joint working group in 2009 [ 1 ].…”

“…Considerable inter-method differences have been reported for both albumin and creatinine measurement procedures [and, therefore, the albumin-to-creatinine ratio (ACR)], but accuracy is unknown and there are no independent reference measurement procedures for albumin and no reference materials for either measurand in urine [ 1 ]. At present most IVD manufacturers provide calibrators with values that are traceable either to the serum reference material ERM-DA470k/IFCC, certified for its albumin content by immunoassay [ 2 ], or to purified albumin preparations.…”

Effect of common storage temperatures and container types on urine protein : creatinine ratios in urine samples of proteinuric dogs

“…In 1 prior study, canine urine was stored in an unspecified container type at room temperature for up to 4 hours and at −20°C for up to 3 months without significantly affecting UPC 27. Storage of human urine at −20°C for as little as 2 weeks has been reported to produce modifications to the albumin molecule that may cause mild preanalytic decreases in measured urine albumin concentration 28, 29. Several other studies confirm a time‐dependent decrease in measured urine albumin concentration at −20°C 30, 31, 32.…”

Chemiluminescence lateral flow immunoassay cartridge with integrated amorphous silicon photosensors array for human serum albumin detection in urine samples

“…In this work, we applied the developed biosensor for the quantitative detection of human serum albumin (HSA) in urine samples, which is considered a biomarker suitable to identify and monitor patients with kidney damage [29]. Normal HSA level in urine is lower than 25 mg L −1 .…”

“…Indeed, the level of urinary albumin excretion indicates kidney damage and it is recognized as a risk factor for pro-gression of kidney disease and damage [29]. In particular, the condition of microalbuminuria can be used to predict diabetic nephropathy [31].…”