Euthyroid Patient with Elevated Serum Free Thyroxine

Summary

DOI: 10.1373/Clinchem.2007.101428

Complete Article
Commentary: Larry J. Kricka
Commentary: Kenneth D. Burman

Student Discussion

George van der Watt,^1* David Haarburger,¹ and Peter Berman¹

¹Division of Chemical Pathology, National Health Laboratory Service, Groote Schuur and Red Cross Children’s Hospitals, University of Cape Town, Observatory, South Africa.
*Address correspondence to this author at: Division of Chemical Pathology, National Health Laboratory Service, Groote Schuur and Red Cross Children’s Hospitals, University of Cape Town, Observatory, South Africa, 7925. Fax +27216585225; e-mail [email protected].

Case Description

A 32-year-old female patient presented complaining of increased flushing, perspiration and heat intolerance of 3 months’ duration. Medical history included idiopathic thrombocytopenic purpura of 4 years’ duration, which had been treated by splenectomy after failed immunosuppression with prednisone and azathioprine and was currently in remission. On examination, she was found to be clinically euthyroid without a goiter. She had also developed a diffuse erythematous popular rash on the face and back, with bullous lesions on the chest. Immunofluorescent antibody studies performed on a punch biopsy of skin were positive for several autoantibodies, leading to a diagnosis of subacute cutaneous lupus erythematosus. This diagnosis was further characterized by positive titers of nuclear and doublestranded DNA autoantibodies in the serum. Thyroid function testing on an Advia Centaur® Immunoassay System (Siemens Medical Solutions Diagnostics) revealed an increased concentration of serum free thyroxine (FT4)2, 90.1 pmol/L (6.97 ng/dL) (reference range 11.5–22.7 pmol/L), a nonsuppressed thyroidstimulating hormone (TSH) concentration of 1.8 mIU/L (1.8 μIU/mL) (reference range 0.35–5.5 mIU/L), and normal free triiodothyronine (FT3) concentration of 4.2 pmol/L (0.33 ng/dL) (reference range 3.5–6.5 pmol/L). Repeat investigation 1 and 2 months later revealed a progressive increase in FT4to 125.3 pmol/L (9.7 ng/dL) and ≥155 pmol/L (≥12.0 ng/dL), respectively. TSH and FT3remained within reference intervals, as did total T4by RIA, at 155 nmol/L (12 μg/dL) (reference range 58–161 nmol/L). Furthermore, she tested positive for antithyroperoxidase antibodies at 110 IU/L (reference range <37 IU/L) and antithyroglobulin antibodies at 149 IU/L (reference range <98.1). An investigation of her disconcordant thyroid function tests was initiated.

Questions to Consider

What are the possible reasons for discrepancies between thyroid function testing and clinical picture?
What are the appropriate next steps to resolve the discrepancy between clinical picture and laboratory results?
What would the clinical picture be if the patient had resistance to thyroid hormone? A pituitary adenoma?

Final Publication and Comments

The final published version with discussion and comments from the experts appears in the July 2008 issue of Clinical Chemistry, approximately 3-4 weeks after the Student Discussion is posted.

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