Competitive ELISA studies of neural thread protein in urine in Alzheimer's disease.

A specific and reliable competitive affinity assay kit has been developed to quantitatively measure neural thread protein (NTP) in first morning urine samples. This assay, called the urine neural thread protein test (UNTP), is a competitive enzyme-linked immunosorbent assay (ELISA) format affinity assay using 32-well microtiter plates. The assay detects UNTP in the 10-60 microg/mL range (an improvement over earlier assays of 10(3) x ), is linear and more reproducible (average coefficient of variation [CV] 6.2% in precision studies). The utility of the assay has been demonstrated in urine samples from patients with Alzheimer's disease (AD) and controls (sensitivity of 90% and specificity of 91%). Test-retest assays of subjects with AD and controls were comparatively stable at intervals of 2 days to 4.5 years, which suggests that positive (elevated) or negative (normal) NTP levels do not fluctuate significantly over time with respect to the cutoff.