Hyperprolactinemia with normal serum prolactin: "Hook effect" a concern in laboratory medicine aspect.

Sir,

I read the interesting case report by Agarwal et al., with a great interest.[1] There are some additional discussions on this case. It is no doubt that “all gynecologists should consider galactorrhea even in women with normal serum prolactin.”[2] The interpretation of the serum prolactin level needs careful consideration. In laboratory medicine, the false negative in prolactin level determination can be expected. A high-dose hook effect in the PRL assay that leads to falsely low serum prolactin level is mentioned in some literatures.[3-6] The hook effect should be considered in any case with a large pituitary mass.[4] A pre-dilution preparation can help in solving this specific false negative problem.[3-6]