Document Detail

Macro-Thyrotropin: A Case Report and Review of Literature.
MedLine Citation:
PMID:  22466337     Owner:  NLM     Status:  Publisher    
Context:Isolated elevation of TSH in the absence of thyroid symptoms can be very rarely caused by a macromolecule formed between TSH and Ig (macro-TSH), confounding the interpretation of thyroid function test results.Objective:We described the use of several commonly available laboratory-based approaches to investigate an isolated TSH elevation [232 mIU/liter; free T(4), 10 pmol/liter (reference interval, 10.0-23.0 pmol/liter), Vitros platform] in a clinically euthyroid elderly gentleman, which led to the diagnosis of macro-TSH.Methods and Results:TSH concentration of the patient was significantly lower (122 mIU/liter) when measured on the Advia Centaur platform. Serial dilution of the patient's sample showed a nonlinear increase in TSH recovery at increasing dilution (nonlinearity). Polyethylene glycol precipitation and mixing the patient's sample with a hypothyroid patient sample showed reduced TSH recovery, suggesting the presence of a high molecular weight interfering substance and excess TSH binding capacity, respectively. Heterophile blocking tube studies and rheumatoid factors were negative. Gel filtration chromatography demonstrated a TSH peak fraction that approximated the molecular size of IgG; together with the excess TSH binding capacity, this indicated the presence of TSH-IgG macro-TSH. A review of 12 macro-TSH case reports showed that samples with macro-TSH produce over-recovery with dilution, return negative results on anti-animal and anti-heterophile blocking studies, and commonly have recovery of less than 20% when subjected to polyethylene glycol precipitation.Conclusion:Macro-TSH is an underrecognized laboratory interference. Routine laboratory techniques described above can help diagnose this rare entity. A close dialogue between the physician and the laboratory is important in approaching such cases.
Tze Ping Loh; Shih Ling Kao; David J Halsall; Sue-Anne Ee Shiow Toh; Edmund Chan; Su Chin Ho; E Shyong Tai; Chin Meng Khoo
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-3-30
Journal Detail:
Title:  The Journal of clinical endocrinology and metabolism     Volume:  -     ISSN:  1945-7197     ISO Abbreviation:  -     Publication Date:  2012 Mar 
Date Detail:
Created Date:  2012-4-2     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0375362     Medline TA:  J Clin Endocrinol Metab     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Departments of Laboratory Medicine (T.P.L.) and Medicine (S.L.K., S.-A.E.S.T., E.S.T., C.M.K.), National University Hospital, Singapore 119074; Department of Clinical Biochemistry (D.J.H.), Addenbrooke's Hospital, Cambridge CB2 2QR, United Kingdom; Saw Swee Hock School of Public Health (E.C.), National University of Singapore, Singapore 117597; and The Endocrine Clinic (S.C.H.), Mount Elizabeth Medical Centre, Singapore 228510.
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