A sensitive radioimmunoassay of atrial natriuretic peptide in human plasma; some guidelines for clinical applications.

We report the development of an in-house RIA for human alpha-ANP. The method requires the extraction of EDTA-plasma on C18-cartridges followed by radioimmunoassay of the eluates with an antibody raised in sheep against human-alpha-ANP coupled to Keyhole Limped Hemocyanin, and a monoiodotyrosyl-alpha-ANP tracer purified with HPLC before use. The assay is precise and sensitive: intra- and interassay coefficients of variation were 8.6% and 11.6%, respectively, and the lower limit of detection was 0.8 pg/tube (4.0 pg/ml plasma). Normal values were 26.0 +/- 15.5 (mean +/- sd) pg/ml plasma (n = 25). Change from supine to sitting position significantly lowered the ANP immunoreactivity. No episodic variations were observed. Our method was applied in a study comparing plasma ANP values in samples of normal persons and CHF-patients. Assay of ANP after extraction using four different antibodies showed significant correlations. HPLC analysis of both plasma of CHF patients and plasma of normal persons revealed the existence of two major immunoreactive components besides alpha-ANP which were not detected in a radioreceptor assay.