Table 2.

Characteristics of Radioimmunoassay (RIA) and Enzyme-Linked Immunosorbent Assay (ELISA) for CRH Measurement

Assay	Cost per Samplea	Assay Durationb	Use of Radioisotopes	Intra-assay/Interassay CV (%)c	Specificity (% Cross-reactivity)	Sensitivity (ng/ml)d
ELISA	US$10−18	4.5−6 hr	No	3−8/5−10	100 (human); 0 (ACTH)	0.08−0.3
RIA	US$12−14; US$242e	3 days	Yes	2−6/8.5−10	100 (human); 0 (ACTH)	0.00095−0.02

Note: ACTH = adrenocorticotropin-releasing hormone; CV = coefficient of variability; CRH = corticotropin-releasing hormone.

^aAverage direct cost per sample if a commercially prepared “kit” is used that simultaneously runs 41 samples in duplicate during a “batch” testing process, along with standards and controls.

^bDoes not include extraction time, which is usually an additional 24 hr.

^cCan vary widely between labs and individuals performing the assays. These are reported by the manufacturers of the bioassay products.

^dAll original reports of sensitivities have been converted to ng/ml for ease of comparison.

^eCost per individual sample, as opposed to samples as part of a batch, as quoted by a local/regional commercial reference laboratory.