Taking Armour Thyroid Before a Thyroid Blood Draw
Patients should not take Armour Thyroid (desiccated thyroid) on the morning of a thyroid blood test as it can significantly affect the results and lead to inaccurate assessment of thyroid function.
Why Timing Matters
- Thyroid function tests (TFTs) are among the most commonly requested laboratory investigations in both primary and secondary care, and accurate results are essential for proper management 1.
- Taking thyroid medication before a blood draw can cause acute fluctuations in thyroid hormone levels that do not reflect the patient's baseline thyroid status 2.
- Serum TSH levels can vary by as much as 50% of mean values on a day-to-day basis, with up to 40% variation of values obtained from serial TSH measurements performed at the same time of day, and medication timing further compounds this variability 3.
Recommended Approach
- Thyroid function tests should preferably be conducted in the morning around 8 am, before taking thyroid medication 3.
- For accurate assessment of thyroid function, patients should hold their Armour Thyroid dose until after the blood draw 2.
- Serial TSH measurements are essential to establish that a thyroid disorder is real and persistent, making the accuracy of each measurement critical 3.
Impact of Taking Medication Before Testing
- Taking Armour Thyroid before a blood test can artificially alter TSH, T3, and T4 levels, potentially leading to:
Special Considerations
- Thyroid hormone dosage must be individualized according to patient response and laboratory findings, making accurate baseline measurements crucial 5.
- Adequate therapy usually results in normal TSH and T4 levels after 2-3 weeks of therapy, but this assessment depends on accurate laboratory values 5.
- Readjustment of thyroid hormone dosage should be made within the first four weeks of therapy, after proper clinical and laboratory evaluations, including accurate serum levels of T4 and TSH 5.
Common Pitfalls in Thyroid Testing
- Laboratory interference from medications is one of the most common pitfalls in thyroid function testing 1.
- Patient requests for tests and treatments can impact physician management of hypothyroidism, making standardized testing protocols important 4.
- When thyroid test results are discordant with the clinical picture, medication timing is one of the first factors to consider 2.
By ensuring proper timing of medication in relation to blood draws, clinicians can obtain more accurate results that truly reflect the patient's thyroid status and make appropriate therapeutic decisions.