During 2002 the US National Academy of Clinical Biochemists published a comprehensive set of guidelines for the Laboratory Support for the Diagnosis and Monitoring of Thyroid Disease. This is a comprehensive overview of the various tests used to diagnose and manage thyroid disease. The guidelines also provide a set of consensus recommendations from an international panel of experts regarding the use and interpretation of the tests.

These consensus recommendations provide patients with a firm and clear statement on what they can expect from their doctors. The guidelines are highly technical and as a result may not be useful to everyone, but the specific recommendations are mostly written in language which can be understood by anyone with a basic understanding of thyroid function and who knows the terminology. Even if you find the language daunting, you can still take a copy to your doctor.

There are 79 specific guidelines for doctors, laboratories and manufacturers. The document extends to 125 pages. I will summarise the guidelines which are relevant to the majority of our members.

Guideline 2: Thyroid Testing of Ambulatory Patients

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Guideline 4: Thyroid Testing of Pregnant Patients

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Guideline 22: TSH Reference Intervals

Serum TSH in healthy people varies during the day from a high in the middle of the night to a low around the middle of the day which is approximately half the overnight maximum.

Population reference intervals are probably too wide because of the inclusion of people who have thyroid dysfunction which is not obvious.

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Guideline 23: Thyroxine Replacement Therapy for Hypothyroidism

• Levothyroxine (L-T4) is the preferred medication for long term replacement therapy.
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TSH tests are not influenced by thyroxine that is taken a few hours before the test, but Free T4 tests are affected. Free T4 levels are significantly increased (~13%) for up to 9 hours after the last dose. On the day of a blood test, that day’s thyroxine dose should not be taken until after the blood sample is drawn.

It is well documented that hypothyroid patients will have serum Free T4 values in the upper third of the reference range when the L-T4 dose is adjusted to bring the serum TSH value into the target range of 0.5 to 2.0 mIU/L.

Guideline 27: Clinical Utility of TSH Assays

• Serum TSH measurement is the most diagnostically sensitive test for detecting mild (subclinical), as well as overt, primary hypo- or hyperthyroidism in ambulatory patients.
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The full NACB Guidelines can be found at http://www.nacb.org/lmpg/thyroid_lmpg_pub.stm

Please discuss these guidelines with your doctor in the context of your situation.

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