National Health and Nutrition Examination Survey

Second Day Exams

See the general documentation on Second Day laboratory exams. See the general documentation on second day laboratory exams. Also, see the documentation for the primary exam data for Laboratory 16.

Urinary albumin and creatinine were measured.

Participants aged 16-69 years were tested.

Urinary creatinine

Creatinine analysis uses a Jaffé rate reaction, in which creatinine reacts with picrate in an alkaline solution to form a red creatinine-picrate complex. The reaction is measured with a CX3 analyzer. The rate of the color development is measured 25.6 sec after sample injection at 520 nm and at 560 nm. The rate difference between the two wavelengths is proportional to the concentration of creatinine in the reaction cup. The procedures described below are the standard protocols of the Fairview University Medical Center (FUMC).

Creatinine, derived from creatine, is released into the plasma at a relatively constant rate. The amount of creatinine per unit of muscle mass is constant; therefore, creatinine is the best indicator of impaired kidney function.

Urinary albumin

A solid-phase fluorescent immunoassay for the measurement of human urinary albumin is described by Chavers et al. The fluorescent immunoassay is a noncompetitive, 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. The urine albumin-antigen complexes with the solid-phase antibody.

This complex then reacts with fluorescein-labeled antibody. The
unattached fluorescent antibody is removed by washing during centrifugation. The fluorescence of the stable solid-phase antibody complex with a fluorometer. The fluorescence is directly proportional to the amount of urine albumin present. The standard curve is 0.5-20 µg/mL albumin.

Increased microalbuminuria is a sign of renal disease and may be predictive of nephropathy risk in patients with insulin-dependent diabetes. 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 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.

Urine specimens were processed, stored and shipped to University of Minnesota, Minneapolis, Minnesota for analysis. Detailed specimen collection and processing instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM). Read the LABDOC file for detailed data processing and editing protocols. The analytical methods are described in the Description of the Laboratory Methodology section.

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

The second day exam data was a convenience sample and thus did not have sample weights. The analysis of NHANES laboratory data must be conducted with the key survey design and basic demographic variables. The NHANES Household Questionnaire Data Files contain demographic data, health indicators, and other related information collected during household interviews. The Phlebotomy Examination File includes auxiliary information such as the conditions precluding venipuncture. The Household Questionnaire Data Files and Phlebotomy Examination File may be linked to the laboratory data file using the unique survey participant identifier SEQN.