title: Misdiagnosis due to the hook effect in prolactin assay.
abstract: OBJECTIVE
  To describe a patient who was misdiagnosed as having a nonfunctional pituitary tumor due to the hook effect on prolactin measurements.
  
  
  METHODS
  A 45-year-old female was admitted with visual disturbances, panhypopituitarism and central diabetes insipidus due to pituitary tumor recurrence. She had been operated 4 times earlier and received cranial irradiation for a suspected nonfunctional pituitary adenoma. Serum prolactin was moderately elevated (164.5 ng/ml), but increased markedly after 1:100 dilution to 14,640 ng/ml. Diagnosis of a giant macroprolactinoma was made and cabergoline was started. Prolactin level normalized and a mild shrinkage of the tumor was achieved after 12 months of therapy.
  
  
  CONCLUSIONS
  The hook effect must be kept in mind while evaluating a giant pituitary adenoma with moderately elevated prolactin levels. This way unnecessary surgical procedures or irradiation may be avoided.
authors.affiliation: Department of Internal Medicine, Division of Endocrinology and Metabolism, School of Medicine, Dokuz Eylul University, Izmir, Turkey. serkan.yener@deu.edu.tr
authors.forename: Serkan
authors.initials: S
authors.lastname: Yener
authors.forename: Abdurrahman
authors.initials: A
authors.lastname: Comlekci
authors.forename: Nuri
authors.initials: N
authors.lastname: Arda
authors.forename: Suleyman
authors.initials: S
authors.lastname: Men
authors.forename: Sena
authors.initials: S
authors.lastname: Yesil
mesh_terms: D000970:Antineoplastic Agents; D000077465:Cabergoline; D020790:Diabetes Insipidus, Neurogenic / Q000209:etiology; D003951:Diagnostic Errors; D004873:Ergolines / Q000627:therapeutic use; D005260:Female; D005938:Glucocorticoids / Q000627:therapeutic use; D006801:Humans; D007018:Hypopituitarism / Q000209:etiology; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000150:complications*; D010911:Pituitary Neoplasms / Q000097:blood / Q000150:complications / Q000175:diagnosis*; D011239:Prednisolone / Q000627:therapeutic use; D011388:Prolactin / Q000097:blood*; D015175:Prolactinoma / Q000097:blood / Q000150:complications / Q000175:diagnosis*; D013974:Thyroxine / Q000627:therapeutic use
chemical_list: D000970:Antineoplastic Agents; D004873:Ergolines; D005938:Glucocorticoids; D011388:Prolactin; D011239:Prednisolone; D000077465:Cabergoline; D013974:Thyroxine