Background

Microalbuminuria (the measurement of trace amounts of albumin protein in the urine) is an important prognostic marker for kidney disease in a variety of disease states such as diabetes mellitus and hypertension. Until recently, conventional qualitative tests (chemical strips or dipsticks) for albuminuria did not detect the small increases in urinary albumin excretion seen in early stages of nephropathy. Newer laboratory tests can now detect very low levels of the protein, leading to improved management for these patients.

OUTLINE

Reference Methods
Clinical Utility
Interfering Diseases or Substances that Alter Levels
Commonly Used Terms
Internet Links

REFERENCE METHODS	CHARACTERIZATION
REFERENCE LEVELS	Excretion of 30–300 mg of albumin/24 h (or 20–200 µg/min or 30–300 µg/mg of creatinine on two of three urine collections
Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Sacks DB, Bruns DE, Goldstein DE, Maclaren NK, McDonald JM, Parrott M. Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Thorn 530, 75 Francis St., Boston, MA 02115, USA.	Clin Chem. 2002 Mar;48(3):436-72 Abstract quote.   BACKGROUND: Multiple laboratory tests are used in the diagnosis and management of patients with diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially. APPROACH: An expert committee drafted evidence-based recommendations for the use of laboratory analysis in patients with diabetes. An external panel of experts reviewed a draft of the guidelines, which were modified in response to the reviewers' suggestions. A revised draft was posted on the Internet and was presented at the AACC Annual Meeting in July, 2000. The recommendations were modified again in response to oral and written comments. The guidelines were reviewed by the Professional Practice Committee of the American Diabetes Association. CONTENT: Measurement of plasma glucose remains the sole diagnostic criterion for diabetes. Monitoring of glycemic control is performed by the patients, who measure their own plasma or blood glucose with meters, and by laboratory analysis of glycated hemoglobin. The potential roles of noninvasive glucose monitoring, genetic testing, autoantibodies, microalbumin, proinsulin, C-peptide, and other analytes are addressed. SUMMARY: The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are of minimal clinical value at the present time, and measurement of them is not recommended.

 

CLINICAL UTILITY	CHARACTERIZATION
MORTALITY
Microalbuminuria and all-cause mortality in 2,089 apparently healthy individuals: A 4.4-year follow-up study. The Nord-Trondelag Health Study (HUNT), Norway. Romundstad S, Holmen J, Kvenild K, Hallan H, Ellekjaer H.	Am J Kidney Dis. 2003 Sep;42(3):466-473 Abstract quote. Background: To date, there are few large follow-up studies of apparently healthy subjects with microalbuminuria (MA). The aim of this study is to examine the association between MA and all-cause mortality in nondiabetic nonhypertensive individuals. Methods: We conducted a 4.4-year mortality follow-up of 2,089 men and women (>/=20 years) without diabetes and treated hypertension, randomly selected from the population-based Nord-Trondelag Health Study (1995 to 1997; n = 65,258). Main outcome measures were adjusted relative risk (RR) for all-cause mortality according to increasing albuminuria, defined at different albumin-creatinine ratio (ACR) levels and in 1/2 or 3 urine samples. The main analysis was performed after exclusion of those with cardiovascular disease. Results: There was a positive association between all-cause mortality and MA. The lowest ACR level associated with increased RR for mortality was the 60th percentile (>/=6.7 microg/mg [0.76 mg/mmol]; RR, 2.4; 95% confidence interval, 1.1 to 5.2), applying 3 urine samples with an ACR greater than the cutoff level. We found a positive association between mortality and increasing numbers of urine samples with an ACR greater than different cutoff levels, in which 3 urine samples were superior. Results persisted after adjusting for several confounders and excluding individuals with untreated hypertension (systolic blood pressure >/= 140 mm Hg/diastolic blood pressure >/= 90 mm Hg) and those who died during the first year of follow-up. Conclusion: Although this study confirms the association of all-cause mortality and ACR level in apparently healthy individuals, intervention trials are necessary before clinical cutoff levels of ACR are established and before screening programs are recommended.
SCREENING
Screening for proteinuria in US adults: a cost-effectiveness analysis. Boulware LE, Jaar BG, Tarver-Carr ME, Brancati FL, Powe NR. Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Md, USA.	JAMA. 2003 Dec 17;290(23):3101-14 Abstract quote.   CONTEXT: Chronic kidney disease is a growing public health problem. Screening for early identification could improve health but could also lead to unnecessary harms and excess costs. OBJECTIVE: To assess the value of periodic, population-based dipstick screening for early detection of urine protein in adults with neither hypertension nor diabetes and in adults with hypertension. DESIGN, SETTING, AND POPULATION: Cost-effectiveness analysis using a Markov decision analytic model to compare a strategy of annual screening with no screening (usual care) for proteinuria at age 50 years followed by treatment with an angiotensin-converting enzyme (ACE) inhibitor or an angiotensin II-receptor blocker (ARB). MAIN OUTCOME MEASURE: Cost per quality-adjusted life-year (QALY). RESULTS: For persons with neither hypertension nor diabetes, the cost-effectiveness ratio for screening vs no screening (usual care) was unfavorable (282 818 dollars per QALY; incremental cost of 616 dollars and a gain of 0.0022 QALYs per person). However, screening such persons beginning at age 60 years yielded a more favorable ratio (53 372 dollars per QALY). For persons with hypertension, the ratio was highly favorable (18 621 dollars per QALY; incremental cost of 476 dollars and a gain of 0.03 QALYs per person). Cost-effectiveness was mediated by both chronic kidney disease progression and death prevention benefits of ACE inhibitor and ARB therapy. Influential parameters that might make screening for the general population more cost-effective include a greater incidence of proteinuria, age at screening (53 372 dollars per QALY for persons beginning screening at age 60 years), or lower frequency of screening (every 10 years: 80 700 dollars per QALY at age 50 years; 6195 dollars per QALY at age 60 years; and 5486 dollars per QALY at age 70 years). CONCLUSIONS: Early detection of urine protein to slow progression of chronic kidney disease and decrease mortality is not cost-effective unless selectively directed toward high-risk groups (older persons and persons with hypertension) or conducted at an infrequent interval of 10 years.

 

INTERFERING DISEASES OR SUBSTANCES THAT ALTER LEVELS

CHARACTERIZATION

Henry JB. Clinical Diagnosis and Management by Laboratory Methods. Twentieth Edition. WB Saunders. 2001.

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Last Updated 1/5/2004

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