National Health and Nutrition Examination Survey

Urinary albumin and urinary creatinine are measured in a random urine collected in the MEC.

Participants aged 6 years and older were eligible to be tested.

Urine specimens are processed, stored and shipped to University of Minnesota, Minneapolis, MN for analysis.

Urinary Albumin
A solid-phase fluorescent immunoassay for the measurement of human urinary albumin is described by Chavers et al. (Chavers, BM, Kidney Int. 1984; 25:576–578). The fluorescent immunoassay is a non-competitive, double-antibody method for the determination of human albumin in urine. Antibody to human albumin is covalently attached to derivatized polyacrylamide beads. The solid-phase antibody is reacted with a urine specimen, and the urine albumin-antigen complexes with the solid-phase antibody. This complex then reacts with fluorescein-labeled antibody. The unattached fluorescent antibody is then removed by washing during centrifugation. The fluorescence of the stable solid-phase antibody complex is determined with a fluorometer; the fluorescence is directly proportional to the amount of urine albumin present. The standard curve is 0.5–20 μg/mL of albumin.

Results of the fluorescent immunoassay (FIA) are reproducible, and the test is accurate and sensitive for the detection of human urinary albumin excretion. It is especially useful for the measurement of low levels of urinary albumin not detectable by dipstick methods. The FIA assay resembles the radio-immunoassay (RIA) in technique and sensitivity without the potential health hazards associated with the handling of isotopes in the laboratory (Chavers, BM, Kidney Int. 1984; 25:576–578). 

Urinary Creatinine using the Roche/Hitachi Modular P Chemistry Analyzer
In this enzymatic method creatinine is converted to creatine under the activity of creatininase. Creatine is then acted upon by creatinase to form sarcosine and urea. Sarcosine oxidase converts sarcosine to glycine and hydrogen peroxide, and the hydrogen peroxide reacts with a chromophore in the presence of peroxidase to produce a colored product that is measured at 546 nm (secondary wavelength = 700 nm). This is an endpoint reaction that agrees well with recognized HPLC methods, and it has the advantage over Jaffe picric acid-based methods that are susceptible to interferences from non-creatinine chromogens.

There were no changes (from the previous 2 years of NHANES) in the laboratories performing the analyses.

Detailed instructions on specimen collection and processing can be found in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM).

The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.

URDACT, the urine albumin/creatinine ratio was created in this data file:

The random urine albumin (URXUMA) in ug/mL and urine creatinine (URXUCR) in mg/dL were converted to the albumin/creatinine ratio (URDACT) in mg/g:

URDACT = URXUMA/URXUCR x 100, round to .01

The NHANES quality control and quality assurance protocols (QA/QC) meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed QA/QC instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM).

Refer to the 2011-2012 Laboratory Data Overview for general information on NHANES laboratory data.

The analysis of NHANES 2011-2012 laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2011-2012 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample weight variables. The Fasting Questionnaire File includes auxiliary information such as fasting status, the time of venipuncture, and the conditions precluding venipuncture. The demographics and fasting questionnaire files may be linked to the laboratory data file using the unique survey participant identifier (i.e., SEQN).

Exam sample weights should be used for analyses. Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial  for further details on the use of sample weights and other analytic issues.