Clinically significant decision levels of hCG.

I read with interest the recent article by Zoltan et al. (1) regarding the use of an algorithm for testing and reporting serum choriogonadotropin at clinically significant decision levels with use of “pregnancy test” reagents. They stated that all human choriogonadotropin (hCG) concentrations (except where noted) were reported in WHO First International Preparation (1st IRP) units. However, when utilizing the work of Kadar et al. (2-4) to establish a discriminatory zone of 6000 to 6500 mt. unitWL to enhance the diagnosis of ectopic pregnancy by sonography, they failed to note that Kadar uses Second International Reference Preparation (2nd IRP) in his work. Given that numerical hCG concentrations based on the 1st IRP are approximately double that of 2nd IRP, it would follow that a discriminatory zone of 12 000-13 000 mt.units/L may be more appropriate if 1st IRP is the standard.