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Kim, Park, Choi, Hong, Kim, Shin, Jang, Kim, Cho, and Lee: High-Dose Hook Effect in Patients with Macroprolactinoma
Original Article
Journal of Korean Society of Endocrinology

Journal of Korean Society of Endocrinology 2005; 20(2): 148-153.

Published online: 20 April 2005

DOI: https://doi.org/10.3803/jkes.2005.20.2.148

High-Dose Hook Effect in Patients with Macroprolactinoma

Sung Yeon Kim, Chul Gu Park, Young Ju Choi, Eui Sil Hong, Sang Wan Kim, Chan Soo Shin, Hak Chul Jang, Seong Yeon Kim, Bo Youn Cho, Hong Kyu Lee

Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.

Received 22 December 2004       Accepted 4 February 2005

Copyright © 2005 Korean Endocrine Society

Abstract

Background

Large amounts of antigen may produce false low values on immunoradiometric assays due to the so-called high-dose hook effect. The physicians' awareness of the possibility of the "high-dose hook effect" will prevent preoperative misdiagnosis. The study was designed to identify the frequency and clinical features of patients with pituitary macroadenomas in whom a high-dose PRL hook effect was documented.

Methods

Our retrospective study involved 42 patients with non-functioning pituitary adenomas (tumor diameter > 30 mm) who underwent transsphenoidal microsurgery from between Jan 1999 to Aug 2004, and 6 patients with non-functioning pituitary adenoma (tumor diameter > 30 mm) were selected for prospective study from Sep 2003 to Feb 2004. Our retrospective study also involved 13 patients with macroprolactinoma for the comparison of the clinical features.

Results

1) The presence of a high-dose hook effect was retrospectively suggested when the PRL levels increased in 4 out of the 42 patients with non-functioning adenomas (tumor diameter > 30 mm) after surgery. Post-operative immunohistochemical staining of their pituitary specimens revealed the tumors to be prolactinoma.
2) Prospectively, dilution testing of the specimens obtained before surgery was done in the 6 patients, and one patient presented with a case of the hook effect. The patient's prolactin level was measured at 53.1 ng/mL before dilution and this was increased up to 22,600 ng/mL upon the 1:1000 dilution.
3) Conclusively, the hook effect was seen in 5 of the 48 patients (10.4%) with non-functioning pituitary adenoma (tumor diameter > 30 mm)
4) Compared with other 2 patient groups (the macroprolactinoma (N=13) group, and the non-functioning pituitary tumor (N=43) group), the high-dose PRL hook effect is more likely to be observed in male patients with large pituitary tumors.

Conclusion

In order to avoid the high-dose hook effect, PRL should be assayed at 1:100~1:200 or even higher dilutions of serum from all patients (and especially the male patients) with large pituitary tumors.

Keywords: High-dose hook effect, Pituitary macroprolactinoma, Immunoradiometric assays

Figures and Tables

Fig. 1
The frequency of high-dose hook effect in non-functioning pituitary macroadenomas (diameter > 30 mm)
jkse-20-148-g001
Table 1
Summary of the Clinical Characteristics of the 5 Patients with High-Dose Hook Effect
jkse-20-148-i001

*Final result of PRL: 22600 ng/ml

†Immunohistochemistry

Table 2
Comparison of Clinical Characteristics in Patients with Macoradenoma
jkse-20-148-i002

*P < 0.05 vs Hook effect adenoma

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