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LETTER TO EDITOR |
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| Year : 2010 | Volume
: 3
| Issue : 3 | Page : 160-161 |
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High-dose hook effect in prolactin macroadenomas: A diagnostic concern
Manika Agarwal, Ananya Das, A Santa Singh
Department of Obstetrics & Gynaecology, North Eastern Indira Gandhi Regional Institute of Health & Medical Sciences (NEIGRIHMS), Mawdiangdiang, Shillong, Meghalaya, India
| Date of Web Publication | 23-Dec-2010 |
Correspondence Address:
Manika Agarwal
Department of Obstetrics & Gynaecology, North Eastern Indira Gandhi Regional Institute of Health & Medical Sciences (NEIGRIHMS), Mawdiangdiang, Shillong - 793 018, Meghalaya
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0974-1208.74164
How to cite this article:
Agarwal M, Das A, Singh A S. High-dose hook effect in prolactin macroadenomas: A diagnostic concern. J Hum Reprod Sci 2010;3:160-1 |
Sir,
I have gone through the letter to the editor regarding laboratory concern for the high-dose hook effect in prolactin assays.The intensity of an antigen-antibody interaction depends primarily on the relative proportion of the antigen and the antibody. A relative excess of either will impair adequate immune complex formation. This is called the "high-dose hook effect" or the "prozone phenomenon." Extremely high levels of prolactin (PRL) can interfere with the assay and produce low readings. This high-dose hook effect may occur because there is not enough antibody to bind to both ends of all antigenic (prolactin) peptides. Most of the PRL is now complexed to a single antibody. Only the few remaining PRL peptides are "sandwiched" and therefore detectable. This results in a falsely low PRL value. Hence, as the antigen concentrations increase, there is a proportional increase in assay titers up to a certain level. Antigen concentrations above this threshold level would "hook" down the assay values resulting in very low measurements. [1],[2] In addition, high-antigen titers can directly dissolve the antigen-antibody complex. [1] In order to avoid the high-dose hook effect, the serum PRL should be estimated in appropriate dilution in all patients with large pituitary tumors. The high-dose PRL hook effect is observed particularly in patients with very large tumors. The immunoradiometric PRL assay must be performed with serum dilution in order to overcome the high-dose PRL hook effect in all new patients with pituitary macroadenomas who may have a prolactinoma. [3] Other suggested remedies for the hook effect include the use of an excess antibody, a cumbersome two-step procedure, and the use of a computer to predict the head to dilute serum samples. [1] Though repeatedly demonstrated in other immunoassays, the high-dose hook effect has only occasionally been observed in chemiluminescence assay systems for PRL estimation. [1]
Whatever the author has cited with references is no doubt of laboratory concern in prolactin assays, but has little relevance to our case report. Our case is not a patient of pituitary prolactinoma with moderate to severe hyperprolactinemia, where the high-dose hook effect of prolactin is of more significance. Moreover, our laboratory uses chemiluminescence assays for prolactin estimation which rarely shows fallacies due to the high-dose effect.
 References | |  |
| 1. | Unnikrishnan AG, Rajaratnam S, Seshadri MS, Kanagasapabathy AS, Stephen DC. The 'hook effect' on serum prolactin estimation in a patient with macroprolactinoma. Neurol India 2001;49:78-80. 
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| 2. | Yener S, Comlekci A, Arda N, Men S, Yesil S. Misdiagnosis due to the hook effect in prolactin assay. Med Princ Pract 2008;17:429-31.
[PUBMED] [FULLTEXT] |
| 3. | St-Jean E, Blain F, Comtois R. High prolactin levels may be missed by immunoradiometric assay in patients with macroprolactinomas. Clin Endocrinol (Oxf) 1996;44:305-9.
[PUBMED] |
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