Erroneous thyroid diagnosis due to over-the-counter biotin.

OBJECTIVES: Biotin is a component of the vitamin B complex used in standard immunoassays to detect serum levels of various hormones and non-hormones, including thyrotropin (TSH) and thyroxine. These assays involve a strong bond between streptavidin and biotin, which serves as an anchor for measured analytes. Large doses of exogenous biotin for the treatment of certain medical conditions have resulted in assay interference, causing TSH to be spuriously lowered. Smaller doses of biotin found in dietary supplements also have caused assay interference. METHODS: We describe four cases in which over-the-counter (OTC) biotin caused erroneous thyroid diagnosis and clinical confusion in patients with preexisting thyroid disease. Serum TSH and thyroxine were measured by the Vitros 5600 assay. CONCLUSIONS: Although the biotin-streptavidin interaction is sensitive for detecting serum levels of TSH, it is subject to interference by exogenous biotin at levels found in OTC products. The widespread use of OTC biotin for cosmetic purposes can adversely affect the diagnosis of the entire spectrum of functional thyroid disorders. Physicians must carefully and routinely question for the use of biotin before thyroid function testing.

In Thyroidectomized Thyroid Cancer Patients, False-Positive I-131 Whole Body Scans Are Often Caused by Inflammation Rather Than Thyroid Cancer.

Objective. To show that I-131 false-positive results on whole-body scans (WBSs) after thyroidectomy for thyroid cancer may be a result of inflammation unassociated with the cancer. Methods. We performed a retrospective image analysis of our database of thyroid cancer patients who underwent WBS from January 2008 to January 2012 to identify and stratify false positives. Results. A total of 564 patients underwent WBS during the study period; 96 patients were referred for 99 I-131 single-photon emission computed tomography (SPECT/CT) scans to better interpret cryptic findings. Among them, 73 scans were shown to be falsely positive; 40/73 or 54.7% of false-positive findings were a result of inflammation. Of the findings, 17 were in the head, 1 in the neck, 4 in the chest, 3 in the abdomen, and 14 in the pelvis; 1 had a knee abscess. Conclusions. In our series, inflammation caused the majority of false-positive WBSs. I-131 SPECT/CT is powerful in the differentiation of inflammation from thyroid cancer. By excluding metastatic disease, one can properly prognosticate outcome and avoid unnecessary, potentially harmful treatment of patients with thyroid cancer.

I-131 SPECT/CT elucidates cryptic findings on planar whole-body scans and can reduce needless therapy with I-131 in post-thyroidectomy thyroid cancer patients.

BACKGROUND: Interpreting I-131 whole-body scans (WBSs) after thyroidectomy for thyroid cancer is not simple. There are scans in which interpretation is speculative because of cryptic findings (CF). Complexity is added in scans that are done a week after an ablative or therapeutic dose of I-131 because not only is I-131-labeled thyroxine (T4) distributed throughout the body, but inorganic I-131 that is derived from the de-iodination of T4 may be also detected. We present our observations regarding the analysis of CF on WBS using I-131 single-photon emission computed tomography (SPECT) in fusion with noncontrast computed tomography (CT), referred to here and elsewhere as I-131 SPECT/CT. METHODS: Forty of 184 WBSs in 38 thyroidectomized thyroid cancer patients were followed up with I-131 SPECT/CTs. The SPECT/CT images were acquired after a tracer dose of I-131 (n=82) or a week after an ablative or therapeutic dose of I-131 (n=102). RESULTS: Among 184 WBSs, 40 (22%) had CF. In 35 patients the WBS was negative for metastatic disease except for the CF and 5 patients had evidence of thyroid cancer in addition to the CF. There were 49 CF in the planar scans that were localized by SPECT/CT. These were characterized as physiological uptake in gingiva, thymus, gall bladder, menstrual blood, uterine fibroid, recto-sigmoid, colon, and bladder. Also observed was uptake in sites that represented nonthyroidal pathology including dental abscess, hiatal hernia, renal cyst, and struma ovarii. SPECT/CT suggested that 10 of the CF were actually of thyroid origin. In 40 SPECT/CT scans, the images contributed to interpreting the scan. In 15 of 40 patients the SPECT/CT analysis of WBS was performed with tracer doses of I-131 and was important for determining whether to administer ablative I-131 treatment. In another 25 patients, in whom SPECT/CT was performed after ablative or therapeutic doses of 131-I, information regarding the characterization of CF by SPECT/CT was useful in determining if thyroid cancer metastases or thyroid remnants were present. CONCLUSIONS: I-131 SPECT/CT is a useful tool to characterize atypical or CF on WBS by differentiating thyroid remnant or cancer from physiologic activity or nonthyroid pathology. In the past, uptake on a WBS that was not explicable as physiologic activity was identified as putative or possible thyroid cancer and generally was treated with I-131. Now, by identifying activity in some possible cancer sites as not thyroid cancer, SPECT/CT can reduce inappropriate treatment with I-131. SPECT/CT of WBS performed after ablative doses of 131-I is useful in determining the nature of CF and therefore likely providing prognostic information.

Radioactivity of blood samples taken from thyroidectomized thyroid carcinoma patients after therapy with (131)I.

BACKGROUND: Occasionally, blood samples may be required from thyroid cancer patients after they have been given the therapy dose of (131)I, as part of necessary medical management of comorbidities. Thus, in the days after (131)I administration, medical health professionals may be involved in the withdrawal, handling, and manipulation of radioactive blood samples. The purpose of this study was to quantify the amount of radioactivity in blood samples taken from thyroidectomized thyroid carcinoma patients after the administration of therapeutic activities of (131)I. METHODS: For dosimetry purposes, serial blood sampling is performed on thyroidectomized thyroid carcinoma patients prior to therapy with (131)I. The quantities of radioactive material present in these blood samples were expressed as a percentage of the administered activity and then extrapolated to the high levels of (131)I used in therapy for 377 patients in this study. The corresponding radiation exposure rate from the blood samples was then calculated to determine what radiation protection methods were required for staff handling these samples. RESULTS: The average amount of radioactivity in a 1 mL blood sample at 1 hour postadministration of 5.5 GBq (150 mCi) of (131)I was 0.2 ± 0.15 MBq (5.4 ± 4.0 µCi). This corresponds to an exposure rate of 1.23 µSv/h (0.123 mrem/h) at 10 cm from the sample. For samples obtained beyond 24 hours after a therapeutic administration of 5.55 GBq (150 mCi), the exposure levels are approximately equal to background radiation. CONCLUSION: The data in this study indicate that the radiation exposure from blood samples withdrawn from thyroidectomized thyroid cancer patients is low. However, to ensure that staff members are exposed to minimal levels of radiation, it is imperative that staff members who are involved in withdrawing, handling, or manipulating radioactive blood samples adhere to the recommended radiation safety practices.

Evidence and thoughts about thyroid nodules that grow after they have been identified as benign by aspiration cytology.

Coherent management of thyroid nodules that grow after being identified as benign will vary depending on their biology. Some are thyroid-stimulating hormone (TSH) regulated, so a dose of levothyroxine that reduces TSH to the lower limits of normal (subsuppression) may prevent or reverse enlargement; others are controlled by poorly understood mechanisms that must be elucidated before effective medical treatment can be designed; a few are autonomous requiring obliteration, and a very few are "missed" malignancies that should be excised.