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

Area of Science:

• Endocrinology
• Clinical Chemistry
• Laboratory Medicine

Background:

• Elevated growth hormone (GH) levels typically indicate acromegaly, a condition characterized by specific clinical signs.
• Pituitary macroadenomas can be associated with GH hypersecretion, but discordant laboratory and clinical findings warrant further investigation.

Observation:

• A 61-year-old female with a pituitary macroadenoma presented with elevated serum GH levels, normal IGF-1, and no acromegaly symptoms.
• Initial GH testing via chemiluminescence immunoassay showed persistent elevation unresponsive to glucose suppression.
• Post-surgical GH levels remained high, suggesting assay interference rather than active acromegaly.

Findings:

• Analysis using three different immunoassays confirmed persistent high GH levels.
• Interference was suspected due to the discrepancy between GH levels and clinical presentation.
• Polyethylene glycol (PEG) precipitation showed only 12% GH recovery, and size-exclusion chromatography confirmed the presence of macro-GH.

Implications:

• Macro-GH can cause false-positive results in various GH immunoassays, leading to misdiagnosis.
• The PEG precipitation method and size-exclusion chromatography are crucial for identifying macro-GH interference.
• Clinicians and laboratory professionals must consider assay interference when laboratory results conflict with patient's clinical status.