J Korean Soc Endocrinol.  2005 Apr;20(2):148-153.

High-Dose Hook Effect in Patients with Macroprolactinoma

• Kim SY
• Park CG
• Choi YJ
• Hong ES
• Kim SW
• Shin CS
• Jang HC
• Kim SY
• Cho BY
• Lee HK

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 >30mm) who underwent transsphenoidal microsurgery from between Jan 1999 to Aug 2004, and 6 patients with non-functioning pituitary adenoma(tumor diameter>30mm) 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 >30mm) 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 53.1ng/mL before dilution and this was increased up to 22,600ng/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 >30mm) 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

MeSH Terms

Diagnostic Errors
Humans
Immunoradiometric Assay
Male
Microsurgery
Pituitary Neoplasms
Prolactin
Prolactinoma*
Prospective Studies
Retrospective Studies
Prolactin

Figure

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  Fig. 1 The frequency of high-dose hook effect in non-functioning pituitary macroadenomas (diameter > 30 mm)

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