Category: Thyroid

Monitor: 15

15 - GRAVES' DISEASE? FALSE POSITIVE RADIOACTIVE IODINE UPTAKE SCAN IN THE PRESENCE OF BIOTIN INDUCED INCREASE IN TSH ANTIBODY AND LOW TSH

Friday, Apr 26
12:00 PM – 12:30 PM

Objective : Many patients are screened for thyroid disorders as they can present with non specific symptoms such as fatigue, weight changes and hair loss. Assay interference with biotin use has led to an increase in spurious results with falsely low TSH and elevated TSH Ab levels. We report a case of a patient on biotin who had low TSH and high TSH Antibody(Ab) levels with normal Free T4 and T3 levels.  She also had a false positive radioactive iodine uptake(RAIU) scan.


Methods :
Case presentation: A 40 year old woman presented to the endocrine clinic with symptoms of palpitations, heat intolerance and anxiety along with weight gain of 10 pounds. Her thyroid function was evaluated and labs showed low TSH level of <0.12 mlU/L with a normal Free T4 and Free T3 level, 1.01 ng/dL and 3.38 pg/mL respectively. TSH Ab was elevated at 2.49 IU/L.  RAIU scan was ordered which showed increased homogeneous uptake of 38.9% at 24 hours. Patient was diagnosed with Grave’s disease and started on methimazole therapy 10 mg daily and 10 mg propranolol twice daily. 


Results : Repeat blood work after 3 months showed mild suppression in TSH of 0.28mlU/L with normal Free T3, Free T4, total T3 and total T4. Her methimazole dose was reduced to 5 mg daily. Repeat testing in 2 months after dose adjustment showed TSH of 0.40, with normal Free T4 and Free T3. Patient continued to have symptoms of palpitations and anxiety while being on methimazole so after 8 months of therapy she stopped methimazole herself. Patient stated she had forgotten to hold biotin prior to lab draws, she was advised again to hold biotin prior to repeat blood work. Repeat tests after being off of methimazole for 5 months and off of biotin showed a normal TSH of 1.07 mlU/L, Free T4 of 0.95 ng/dL and Free T3 of 3.11 pg/mL. Repeat TSH Ab off of biotin was also normal <0.9 IU/L.


Discussion : Patient had low requirements of methimazole, lack of resolution of symptoms after starting methimazole, persistently normal Free T4 and Free T3 before and during therapy. She also had normalization of TSH Ab and TSH after stopping biotin therapy, off of methimazole. These findings suggests that the abnormal TSH and TSH Ab were likely due to biotin and thyroid RAIU scan was false positive.


Conclusion : Physicians should be cautious in such cases and make sure patients hold biotin prior to blood work and be mindful that RAIU scan results are not 100% accurate. Certain medications can lead to increased uptake on RAIU scan such as rifampin, phenytoin, carbamazepine, and phenobarbital. RAIU scans can also show increased uptake in patients who have a very low iodine diet.

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Nashmia Riaz

Fellow
UTMB

Division of Endocrinology and Metabolism and Division of General Internal Medicine, Department of Medicine, University of Texas Medical Branch

Madiha IQBAL.. Khan

Faculty
UTMB

Division of Endocrinology and Metabolism and Division of General Internal Medicine, Department of Medicine, University of Texas Medical Branch

Arjun Haridas

FELLOW- DIVISION OF ENDOCRINOLOGY
UNIVERSITY OF TEXAS MEDICAL BRANCH- GALVESTON, Texas

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