Macro-GH - A clinical entity causing a diagnostic challenge - A case report.

Aim: Presentation of a new case of a patient with macro-GH, that may interfere with different GH assays leading to false-positive results in serum samples.

Case Presentation: A 61-year-old female was referred with a pituitary macroadenoma and elevated growth hormone levels. The laboratory tests showed increased fasting GH level, measured by a sandwich chemiluminescence immunoassay (LIAISON® XL) without suppression on oral glucose tolerance test and normal IGF-1. The patient did not have the typical signs and symptoms of acromegaly. The patient underwent a transsphenoidal resection of a pituitary tumor, showing only α-subunit immunostaining. Postoperative GH levels remained elevated. An interference in the determination of GH level was suspected. GH was analyzed by three different immunoassays, UniCel DxI 600, Cobas e411 and hGH-IRMA. Heterophilic antibodies and rheumatoid factor were not detected in serum sample. GH recovery after precipitation with 25 % polyethylene glycol (PEG) was 12 %. Size-exclusion chromatography confirmed the presence of macro-GH in serum sample.

Conclusion: If results of laboratory tests are not consistent with the clinical findings, the presence of an interference within immunochemical assays could be suspected. To identify interference caused by the macro-GH, the PEG method and size-exclusion chromatography should be used.