ACCURACY OF SINGLE CONCENTRATION ESTIMATIONS OF PLATELET ANGIOTENSIN-II RECEPTOR NUMBER - ITS USEFULNESS IN SCREENING FOR PREGNANCY-INDUCEDHYPERTENSION

Platelet angiotensin II (AngII) receptor number has been suggested as a screening test for pregnancy-induced hypertension. However, markedly different false-positive rates have been reported, perhaps the result of differing methods used. We sought therefore to compare the two met hods. Platelet AngII receptor number was determined by saturation anal ysis with computerized curve fitting and specific binding at a single radioligand concentration. The two methods were compared by correlatio n and by plotting their differences v their means, to determine their limits of agreement. There were significant correlations between the v alue obtained by saturation analysis and each of the three single liga nd concentrations studied (1 nmol/L, P < .001; 500 pmol/L, P < .001; a nd 250 pmol/L, P < .01). However, for none of the three did the regres sion line approach the line of equality. Assessment of agreement by co mparing differences and means for each subject showed increasing scatt er with increasing receptor number and 95% confidence intervals too la rge to be clinically relevant. We conclude that the receptor number es timated from specific binding at one ligand concentration differs sign ificantly from that obtained by saturation analysis. The limits of agr eement of the two methods are wide and we urge caution in the use of s ingle ligand concentration methods for estimating binding site densiti es.