More on "hook effects" in immunometric assays for prostate-specific antigen.

to be avoided. Berthed and Rey (1) have also reported enormous crossreactivityof hydrocortisonehemisuccinate in the “Rianen” RIA kit for cortisol determination. An issue of Clinical Chemistry (1983;29:890-953) reports the commercial availability of(then)more than 27 cortisol RIA kits.Methodologically, these kits were divided into three groups according to the different antibodies used: antibodies against cortisol21-HS-BSA,antibodies against prednisolone-3-CMO-BSA, and antibodies against cortisol-6-hemisuccinate-BSA (2,3). The specificity for cortisol depends on the specificity of the antibodies used. Briefly, in the casedescribed above, kits in which antibodies against prednisolone-3-CMO-BSA and cortisol6-HS--BSA are used showed a significant cross-reactivity for methylpredrnsolone and prednisolone (3). However, kits in which antibodies against cortisol-21-HS--BSA are used show a signif. icant cross-reactivity for deoxycortisol, 21-deoxycortisol, 17a-hydroxyprogesterone, and corticosterone (4). This consideration should always be borne in mind, because misleading results may ensue.