THYROID FUNCTION ALGORITHM - Metropolitan Medical

1 THYROID FUNCTION ALGORITHM Metro Lab s THYROID ALGORITHM is based on the approach recommended by the Mayo Clinic. Use of this algorithmic approach allows physicians to make timely diagnoses which can reduce the cost of care by the elimination of expensive redraws, repeat orders, and unnecessary physician time. The appropriate tests are all performed automatically. The ALGORITHM consists of these tests: The Sensitive-TSH (s-TSH) This is the best screening assay for both hypo and hyperthyroidism. Most results will be normal and there is no further testing. The Free T4 (FT4) is performed if the s-TSH is less than or above mIU/L. The Total T3 Low s-TSH with elevated FT4 is found with hyperthyroidism. In a small subset of hyperthyroid patients, hyperthyroidism may be caused by overproduction of T3 (T3 thyrotoxicosis).

2 The performance of the Total T3 will identify this subgroup. The Total T3 is measured on all specimens with suppressed s-TSH and normal FT4 concentrations. Thyroperoxidase Antibodies (TPO) is performed if the s-TSH is greater than mIU/L and the FT4 is low, together indicating hypothyroidism due to disease in the THYROID gland. In some patients with hypothyroidism or hyperthyroidism, lymphocytes make antibodies against the THYROID that either damage or stimulate the gland. Measuring levels of THYROID antibodies may help diagnose the cause of THYROID problems. Thyroperoxidase antibodies are found in patients with Hashimoto s Thyroididis, myxedema, and Graves Disease. Anti-TPO antibodies will be measured in all specimens with elevated s-TSH concentrations.

3 A Hospital Best Practice: Screening for THYROID Dysfunction should be avoided in hospitalized patients. This does not mean THYROID FUNCTION should not be measured when THYROID disease is a serious diagnostic consideration in explaining a hospitalized patient s acute problem. However, non-thyroidal illness has a negative impact on both the sensitivity and specificity of s-TSH ( in acute illness all THYROID indices have been shown to yield false positive results). s-TSH levels may also change or fluctuate as the result of: Physiologic Variables Medications General Physical Conditions or Environment Age Pregnancy Genetics Antidepressants (Zoloft, Paxil, Prozac and Lithium), Aspirin, Heparin, Steroids, Soy products, Herbs/Supplements Acute stress ( hospitalization), fatigue, poor nutrition, chronic illness ( rheumatoid arthritis), seasonal changes 1.

4 Endocr Pract. 2008;14;90:1180-1197. 2. Arch Int Med. Vol 159:1999;658-665. 3. CAP Today 2007. Vol 21 No. 2;70-72. 4. BMJ 2003. Feb 8;326;296-7. Metropolitan Medical Laboratory, PLC 1520 Seventh Street, Moline, IL 61265 309-762-8555 1828 E. Locust Street, Davenport, IA 52803 563-324-0471 Time to Say Good-Bye to the Laboratory T3-Uptake Laboratory performed T3-Uptake values, (not to be confused with the nuclear medicine test, Radioactive THYROID Uptake), are a FUNCTION of THYROID hormone binding capacity of serum. As a result many conditions result in abnormal T3-Uptake values even when no THYROID malfunction is present. Combining this value with Total T4, called the Free Thyroxine Index (FTI) was sufficient in the past when you couldn t directly measure Free T4 (FT4).

5 As far back as 1993 the American THYROID Association suggested: The measurement of the serum s-TSH level complemented by an appropriate free thyroxine (FT4) value represents the best and most efficient combination of tests for diagnosis and follow-up of most patients with THYROID disorders . With s-TSH and FT4 you can make the diagnosis of virtually all forms of THYROID disease. Reference labs today, almost without exception, consider the T3-Uptake obsolete. To continue to offer the T3-Uptake is a disservice to patients and physicians and will be discontinued as of April 6, 2009. NEW REFERENCE RANGE FOR THYROID FUNCTION IN PREGNANCY ACOG endorses measuring s-TSH in early pregnancy. This is a special case needing a reduced upper limit for the s-TSH reference range.

6 In the first 13 weeks the fetus is totally dependent on maternal thyroxine, especially for the development of the brain and neuronal connections. Even mild thyroxine deficiency, so-called subclinical hypothyroidism, is associated with pre-term delivery and may have subsequent effects on the development of a child. The upper limit of normal for s-TSH: in the first trimester of pregnancy: mIU/L in the second and third trimester of pregnancy: mIU/L Order an FT4 if the s-TSH limit is exceeded. The lower limit of the reference range is unchanged. These Pregnancy Reference Range limits will be listed on all s-TSH reports for women under 50 years. THYROID FUNCTION ALGORITHMNon-hospitalized patients without known or suspected pituitary diseaseSensitive TSH** < - - mIU/L> mIU/LFree T4If Free T4 normalTotal T3 BorderlineLow TSHH ypothyroidSuspectNormal THYROID .

7 No further testing indicatedFree T4andThyroperoxidase (TPO) AntibodiesFree T4**S-TSH= 3rd Generation Assay: Functional Sensitivity mIU/LReference: Modified from Mayo Medical Laboratories Communique March suspect Sensitive TSH** Order Code 10016 for complete ALGORITHM + + To order the sTSH individually, use ordering code 10015 mlU/L - mlU/L > mlU/L