Camilla Bøgelund Larsen1,2, Eva Rabing Brix Petersen3, Martin Overgaard2,4, Steen Joop Bonnema1,2. 1. Department of Endocrinology, Odense University Hospital, Odense, Denmark. 2. Department of Clinical Research, University of Southern Denmark, Odense, Denmark. 3. Department of Clinical Biochemistry and Immunology, Hospital of Southern Jutland, Aabenraa, Denmark. 4. Department of Clinical Biochemistry and Pharmacology, Odense University Hospital, Odense, Denmark.
Abstract
INTRODUCTION: Analytical problems should be considered in case of a discrepancy between the results of biochemical tests and the clinical findings. Macro-hormones often artefactually elevate biochemical tests. CASE PRESENTATION: A young male was referred with persistently elevated TSH (148 mIU/L) measured by a sandwich electrochemiluminescence immunoassay, ECLIA (Cobas; Roche, Basel, Switzerland). The patient's complaints were unspecific, and he appeared clinically euthyroid. The plasma levels of free T4 and free T3 were within the normal range, thyroid autoantibodies were negative, and thyroid ultrasonography was normal. During a short trial of thyroid hormone substitution, the level of TSH decreased to near-normal levels, but hyperthyroid symptoms emerged. TSH analysed by a different immunoassay (Architect; Abbott, Chicago, IL, USA) yielded similar results. In addition, serial dilutions were performed showing linearity, without detection of heterophilic antibody interference. Gel filtration chromatography confirmed the presence of macro-TSH. CONCLUSION: The patient harboured macro-TSH, which is a rare condition. The complex binding of TSH to other plasma proteins, most often immunoglobulins, results in elevated plasma TSH. However, the biologically active fraction of TSH is normal, reflected by clinical and biochemical euthyroidism.
INTRODUCTION: Analytical problems should be considered in case of a discrepancy between the results of biochemical tests and the clinical findings. Macro-hormones often artefactually elevate biochemical tests. CASE PRESENTATION: A young male was referred with persistently elevated TSH (148 mIU/L) measured by a sandwich electrochemiluminescence immunoassay, ECLIA (Cobas; Roche, Basel, Switzerland). The patient's complaints were unspecific, and he appeared clinically euthyroid. The plasma levels of free T4 and free T3 were within the normal range, thyroid autoantibodies were negative, and thyroid ultrasonography was normal. During a short trial of thyroid hormone substitution, the level of TSH decreased to near-normal levels, but hyperthyroid symptoms emerged. TSH analysed by a different immunoassay (Architect; Abbott, Chicago, IL, USA) yielded similar results. In addition, serial dilutions were performed showing linearity, without detection of heterophilic antibody interference. Gel filtration chromatography confirmed the presence of macro-TSH. CONCLUSION: The patient harboured macro-TSH, which is a rare condition. The complex binding of TSH to other plasma proteins, most often immunoglobulins, results in elevated plasma TSH. However, the biologically active fraction of TSH is normal, reflected by clinical and biochemical euthyroidism.
Authors: Eline Verhoye; Annick Van den Bruel; Joris R Delanghe; Evi Debruyne; Michel R Langlois Journal: Clin Chem Lab Med Date: 2009 Impact factor: 3.694