Received on May 26, 2008
Accepted on August 6, 2008

General Clinical Chemistry

Current Issues in Measurement and Reporting of Urinary Albumin Excretion

¹ Department of Pathology, Virginia Commonwealth University, Richmond, VA
² Department of Pathology, University of Virginia Medical School, Charlottesville, VA
³ Department of Laboratory Medicine, Warren Magnuson Clinical Center, National Institutes of Health, Bethesda, MD
⁴ Laboratory of Clinical Biochemistry, Haukeland University Hospital and The Norwegian Quality Improvement of Laboratory Services in Primary Care (NOKLUS), Bergen Norway
⁵ Hamilton Regional Laboratory Medicine Program, Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
⁶ Department of Laboratory Medicine, Asahikawa Medical College, Asahikawa, Japan
⁷ Mayo Clinic Renal Function Laboratory, Department of Laboratory Medicine and Pathology, Mayo Clinic Division of Nephrology and Hypertension, Department of Internal Medicine, Rochester, MN
⁸ Canadian External Quality Assessment Laboratory and Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada
⁹ Department of Chemical Pathology, St Vincent's Hospital Sydney, Sydney, Australia
¹⁰ Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, MD
¹¹ Renal Division, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA
¹² National Kidney Disease Education Program, National Institute for Diabetes and Digestive Diseases, National Institutes of Health, Bethesda, MD
¹³ Department of Pathology, Virginia Commonwealth University, Richmond, VA, and Department of Pathology, University of Virginia Medical School, Charlottesville, VA, and Department of Laboratory Medicine, Warren Magnuson Clinical Center, National Institutes of Health, Bethesda, MD, and Laboratory of Clinical Biochemistry, Haukeland University Hospital and The Norwegian Quality Improvement of Laboratory Services in Primary Care (NOKLUS), Bergen Norway, and Hamilton Regional Laboratory Medicine Program, Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada, and Department of Laboratory Medicine, Asahikawa Medical College, Asahikawa, Japan, and Mayo Clinic Renal Function Laboratory, Department of Laboratory Medicine and Pathology, Mayo Clinic Division of Nephrology and Hypertension, Department of Internal Medicine, Rochester, MN, and Canadian External Quality Assessment Laboratory and Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada, and Department of Chemical Pathology, St Vincent's Hospital Sydney, Sydney, Australia, and Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, MD, and Renal Division, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, and National Kidney Disease Education Program, National Institute for Diabetes and Digestive Diseases, National Institutes of Health, Bethesda, MD

^* To whom correspondence should be addressed. E-mail: gmiller{at}vcu.edu.

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.