[Don't be guided purely by numbers: false increased TSH values due to analytical interference]

Area of Science:

• Endocrinology
• Clinical Chemistry

Background:

• Physicians rely on laboratory values for diagnosis and treatment.
• Discrepancies between clinical presentation and lab results necessitate considering analytical interferences.
• Analytical interference can lead to falsely elevated or decreased laboratory values.

Observation:

• A 57-year-old male presented with fatigue and palpitations, exhibiting high thyroid-stimulating hormone (TSH) and normal free thyroxine (FT4) levels.
• Despite the absence of clear clinical symptoms, the patient was treated for subclinical hypothyroidism with levothyroxine.
• Continued high TSH and rising FT4 levels led to the development of thyrotoxicosis.

Findings:

• The patient's elevated TSH was ultimately identified as a false positive result.
• Macro TSH, a rare interference, was the cause, involving TSH binding with IgG to form larger molecules.
• These macro TSH conjugates interfere with laboratory assays, producing falsely elevated TSH readings.

Implications:

• Recognizing rare analytical interferences like macro TSH is crucial for accurate thyroid disorder diagnosis.
• Misinterpretation of falsely elevated TSH can lead to incorrect treatment and adverse health outcomes.
• This case highlights the importance of correlating laboratory findings with clinical assessments to avoid diagnostic errors.