Measuring Urinary Albumin Excretion

A number of semiquantitative assays for screening for increased UAE are available. These test strips, most of which are optimized to read positive at a predetermined albumin concentration, have been recommended for screening programs. In view of the wide variability in UAE, it must be borne in mind that a normal value does not rule out renal disease. Because these assays measure albumin concentration, dilute urine may yield a false-negative test result. Refrigerated urine samples should be allowed to reach at least 10 °C before analysis. Albu Screen and Albu Sure (Cambridge Life Sci- 

All the sensitive, specific assays for urine albumin use immunochemistry with antibodies to human albumin. Four 

Standard RIA methods have been described with I-labeled albumin and antialbumin antiserum, but reagents are radioactive and have a short shelf life. Commercial Idts are available. 

Enzyme-Linked Immunosorbent Assay Both competitive and sandwich ELlSAs are available. Although the competitive ELISA is faster because it uses only one incubation with an antibody, it is reported to be less sensitive and exhibits large imprecision. ELISA can be performed on a microplate reader, allowing semiautomation. In the sandwich assay, the primary antibody (antialbumin antiserum) is fixed on the plastic plate, which is then washed. Samples, controls, and calibrators are added, and the complexes detected and quantified by a second antibody conjugated to an enzyme label. 

An ELISA method is described in the Evolve site that accompanies this book. 

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Holl RW, Grabert M, Heinze E, Debatin KM. Objective assessment of smoking habits by urinary cotinine measurement in adolescents and young adults with type 1 diabetes. Reliability of reported cigarette consumption and relationship to urinary albumin excretion. Diabetes Care 1998 21 787-791. 

There are no reports of human nephrotoxicity caused by release of mercury from amalgam fillings. This is supported by experimental data from ten humans where standard measurements of renal function (glomerular filtrate rate, urinary albumin excretion, P2-microglobuUn, N-acetyl-P-D-glucosaminidase) were monitored before and 60 days after the removal of mercury amalgam fillings [102]. 

By age 11 years his renal function decreased, as measured by a creatinine clearance of 71 mL/min (normal is 105 mL/min). He also developed protein-losing nephropathy with a 24-hour urinary protein excretion of 600 mg that increased to 14 g after albumin infusions... 

Some biologically active vitamin Be is excreted in the urine, and a number of studies have assessed nutritional status by microbiological measurement of this excretion it is difficult to interpret the results in terms of underlying nutritional status rather than as a reflection of recent intake, although the excretion does fall in deficiency (Sauberlich et al., 1972, 1974). A possibly important source of error here is that minor renal damage, resulting in albuminuria, will result in a considerable increase in urinary albumin-bound pyridoxal phosphate. 

A 24 hour unine collection showing an albumin excretion at a rate of 20 to 200 pg/ min or a urinary concentration of 30 to 300 mg/L measured on at least two occasions is refeerred to as microalbuminuria. Urinary albumin levels above these values are called "macroalbuminuria", or sometimes just albuminuria. To compensate for the variablility in urine concentra-... 

In the past, measurement of the urinary protein excretion rate was accomplished using a 24-hour urine collection in patients at risk for CKD. Use of an untimed "spot" urine sample with either an albumin-specific dipstick or measurement of albumin creatinine ratio is now recommended by some because it is more convenient than the extended-interval urine collection. 

Although not a quantitative measure of renal function, urinary microalbuminuria has been identified as an early marker of renal disease in patients with diabetic nephropathy and numerous other conditions, such as hypertension and obesity. Patients with microalbuminuria (30 to 300 mg/day) on at least two occasions or overt albuminuria (>300 mg/day) should begin to receive pharmacotherapy. For children, microalbuminuria is considered present if albumin excretion exceeds 0.36 mg/kg per day, and overt albuminuria has been defined as an excretion rate that exceeds 4 mg/kg per day. The urinary albumin creatinine ratio is also an accurate predictor of 24-hour proteinuria, a marker of renal disease. Guidelines for monitoring indicate that a urine albumin creatinine ratio of >30 mg/g places the patient at increased risk of developing diabetic nephropathy and is an indication for the initiation of pharmacotherapeutic intervention. Microalbuminuria has also been suggested as a risk factor for renal dysfunction among patients with essential hypertension. ... 

Microalbuminuria is defined as an increase in urinary excretion of albumin above the reference mterval for healthy nondiabetic subjects but at a concentration that is not generally detectable by crude clinical tests, such as dipsticks designed to measure total protein. With improved methodology, these low concentrations of albumin can now be measured, and microalbuminuria is now considered a clinically important indicator of deteriorating renal function in diabetic subjects. For example, it is now accepted by both European and U.S. diabetes societies that regular screening... 

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