Narva, Andrew S.

Abstract Background Urine albumin is a key laboratory test used for classification, assessment of risk, and monitoring treatment of patients with chronic kidney disease. Urine albumin measurement results are not standardized among different measurement procedures. Consequently, clinical guidelines using fixed decision values for urine albumin cannot be applied consistently. Content Isotope dilution mass spectrometry reference measurement procedures and certified reference materials are being developed to enable standardization of immunoassay measurement procedures for urine albumin. A previous report determined calibration bias was the major error source for differences in results among different measurement procedures for urine albumin. Performance goals for between-day precision, ≤6% CV above 15 mg/L, and for specimen-specific effects, ≤6% CV, were established on the basis of the performance capability of current measurement procedures. The biological variation model was used to estimate a total allowable error of ≤24%–30% and from that the goal for bias of ≤7%–13%. Summary A reference system of higher-order certified reference materials and reference measurement procedures is being developed to enable standardization of urine albumin measurement results. Goals have been established for total allowable error, specimen-specific effects, imprecision, and bias to facilitate efforts to standardize urine albumin measurement results.

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.