Hyperthyroidism: Screening and Diagnostic Testing

University of the East
Ramon Magsaysay Memorial Medical Center, Inc.
GRADUATE SCHOOL
Aurora Boulevard, Quezon City

The doctor will perform physical examinations and order blood tests to measure the hormone levels. Hyperthyroidism is diagnosed when when the levels of T4 and T3 are higher than normal and the level of TSH is lower than normal. (Cooper, McDermott, & Wartofsky, 2006)

It would be observed in a physical examination an enlarged thyroid gland and a rapid pulse. There might be the presence of moist, smooth skin and a tremor of the fingertips. The reflexes are likely to be fast, and the eyes may have some abnormalities in the occurrence of Graves’ disease. (American Thyroid Association, n.d.)

Baskin et al. (2008) enumerated the thorough examination of the following:
• Weight and blood pressure
• Pulse rate and cardiac rhythm
• Thyroid palpation and auscultation (to determine thyroid
size, nodularity, and vascularity)
• Neuromuscular examination
• Eye examination (to detect evidence of exophthalmos
or ophthalmopathy)
• Dermatologic examination
• Cardiovascular examination
• Lymphatic examination (nodes and spleen)

The most reliable test for diagnosing hyperthyroidism is the measurement of serum TSH concentration by a reliable laboratory using a third-generation immunoradiometric methodology. Current methods should allow distinguishing normal TSH levels (> 0.1 mU/l) from that indicating the presence of hyperthyroidism: low (< 0.1 mU/l) and undetectable levels (< 0.01 mU/l) (Fadel et al., 2000). Volkov, Merkin, Press, & Peleg (2009) meanwhile states that normal blood levels are as follows: TSH- 0.39-4.0ulU/ml, Free T3 - 2.3-4.2pg/ml, Free T4 - 0.8-1.5ng/dl.

United State Preventive Services Task Force (2004), Screening for Thyroid Disease sited that thyroid dysfunction can be done in variety ways. TSH is usually recommended because it can detect abnormalities before other test reveal abnormal results. TSH also has higher sensitivity (98%) and specificity (92%) that the other thyroid test, they added. The accuracy of TSH screening in primary care patients is difficult to evaluate, as TSH is often considered the “gold standard” for assessing thyroid function.

Moore E. (n. d.) also added that TSH test result is an excellent tool for screening new patients for thyroid disease, although in some cases of autoimmune thyroid disease, it will lead to inaccurate results. She also added that in screening for thyroid disease, the TSH test is the best early indicator of thyroid dysfunction. In autoimmune thyroid disease, TSH levels fall in people with TSH receptor antibodies (TRAb). Both the stimulating TRAb seen in Graves’ disease and Hashitoxicosis, and the blocking TRAb seen in atrophic hypothyroidism are recognized by the pituitary gland as if they were TSH. Erroneously thinking that blood levels of TSH are adequate, the pituitary gland secretes less TSH. For this reason, patients with Graves’ disease may have low TSH levels even after they become euthyroid (normal thyroid function). Patients with Graves’ disease are considered euthyroid as soon as FT4 falls. With any clinical laboratory test, correlation must be made with other laboratory results, clinical signs and symptoms, and a careful medical history.

If there the TSH level is abnormal, there should be further testing. Undetectable TSH level is a diagnostic of hyperthyroidism. (Reid & Wheeler, 2005)

“Consequently, it is recommended that all adults have their serum TSH concentration measured beginning at age 35 years and every 5 years thereafter, the interval at which a periodic health examination has been advocated by the US Preventive Services Task Force. The American Thyroid Association recommends that adults be screened for thyroid dysfunction by measurement of the serum TSH concentration, beginning at age 35 years and every 5 years thereafter. The indication for screening is particularly compelling in women, but it may also be justified in men as a relatively cost-effective measure in the context of the periodic health examination. Individuals with clinical manifestations potentially attributable to thyroid dysfunction and those with risk factors for its development may require more frequent serum TSH testing.” (Ladenson et al., 2000)

The radioactive iodine uptake and scan can be helpful in determining the etiology of hyperthyroidism and can help in directing treatment. Radioactive iodine uptake measures how much of the radioactivity given orally has been taken up by the thyroid over a period of time and is typically reported as a percentage. The scan complements the uptake and shows how the activity is distributed in the thyroid. (Siraj, 2008)

Differential Diagnosis

Graves’ disease
Laboratory diagnosis
Free tri-iodothyronine and thyroxine concentrations in serum are up, and serum thyrotropin is unnoticeable in most patients.

“The 24-h radioactive iodine uptake can be very useful when trying to distinguish mild Graves’ disease from silent or postpartum thyroiditis in which the 24-h uptake of radioactive iodine will be low.” (Cooper, 2003)

TSH level measured with use of a sensitive assay is always suppressed, and the thyroid scan shows diffuse isotope uptake and sometimes a pyramidal lobe. Also in geriatric patients, Graves’ disease may be more difficult to diagnose and may manifest only with cardiac findings or weight loss (apathetic or masked thyrotoxicosis). (Baskin et al., 2008)

Toxic adenoma
A toxic adenoma (“hot nodule”) is associated with a low TSH level, with or without a high free T4 or T3 estimate. The thyroid scan reveals a functioning nodule and suppression of the extranodular thyroid tissue. Toxic multinodular goiter has the same characteristics and similar laboratory findings as those associated with a toxic nodule, but the thyroid gland is variably enlarged and composed of multiple nodules. In both cases, radioactive iodine uptake is usually increased but may be in the normal range. (Baskin et al., 2008)

Pregnancy
Hyperthyroid symptoms (heat intolerance and palpitations) are ordinary in pregnancy therefore diagnosis might not be obvious. Laboratory testing might prove difficult because increased thyroid-binding globulin raises total serum thyroxine, and because serum thyrotropin concentrations might be low in healthy pregnant women at the end of the first trimester. (Cooper, 2003)



Reference:

American Thyroid Association. (n.d.). Hyperthyroidism. Retrieved on February 15, 2010 from www.thyroid.org

Baskin, H.J., Cobin, R.H., Duick, D.S., Gharib, H., Guttler, R.B., Kaplan, M.M., Segal, R.L., and the American Association of Clinical Endocrinologists. (2008). American Association of Clinical Endocrinologists medical guidelines for clinical practice for the evaluation and treatment of hyperthyroidism and hypothyroidism. Endocr Pract, 14(6):802-3. Retrieved on February 15, 2010 from http://www.aace.com/pub/pdf/guidelines/hypo_hyper.pdf

Cooper, D. (2003). Hyperthyroidism. The Lancet, Volume 362, Issue 9382, Pages 459 – 468. doi:10.1016/S0140-6736(03)14073-1

Cooper, D., McDermott, M., and Wartofsky, L. (2006). Hyperthyroidism. The Journal of Clinical Endocrinology & Metabolism, Vol. 91, No. 7 0. Retrieved on February 15, 2010 from http://jcem.endojournals.org/cgi/content/full/91/7/0

Fadel, B., Ellahham, S., Ringel, M., Lindsay, JR. J., Wartofsky, L., and Burman, K. (2000). Hyperthyroid Heart Disease. Clin. Cardiol, 23, 402–408. DOI: 10.1002/clc.4960230605

Ladenson, P., Singer, P., Ain, K., Bagchi, N., Bigos, S.T., Levy, E., Smith, S., and Daniels, G. (2000). American Thyroid Association Guidelines for Detection of Thyroid Dysfunction. Arch Intern Med, 160:1573-1575. Retrieved on February 15, 2010 from http://www.thyroid.org/professionals/publications/documents/GuidelinesdetectionThyDysfunc_2000.pdf

Moore E. (n. d.). THE TSH THYROID FUNCTION TEST: When Thyrotropin Isn't The Gold Standard. retrieved February 16, 2010 from http://www.elaine-moore.com

Reid, J. and Wheeler, S. (2005). Hyperthyroidism: Diagnosis and Treatment. Am Fam Physician, 72:623-30, 635-6. Retrieved on February 15, 2010 from EBSCohost.

Siraj, E. (2008). Update on the Diagnosis and Treatment of Hyperthyroidism. Journal of Clinical Outcomes Management, 15 (6): 298–307. Retrieved on February 15, 2010 from http://www.turner-white.com/memberfile.php?PubCode=jcom_jun08_hyperthyroidism.pdf.

U.S. Preventive Services Task Force ( January, 2004). Screening for Thyroid Disease. retrieved February 16, 2010 from website:http://www.ahrq.gov/clinic/3rduspstf/thyroid/thyrrs.pdf

Volkov, I., Merkin, L., Press, Y., and Peleg, R. (2009). Diplopia as the Sole Manifestation of Hyperthyroidism. The Internet Journal of Family Practice, Volume 4 Number 2. Retrieved on February 15, 2010 from EBSCohost.