With exogenous administration of hormones, the timing between the test sampling and the prior dose of therapy must be taken into consideration when the test results are interpreted, no matter which method is used to test hormones levels.
The best method of testing hormones is to use a laboratory that considers both the dosage route and timing of the last dose of hormone in determining the expected range for that hormone. Ideally, when a patient is on hormone therapy, testing should be done at an interval of time that avoids peaks or troughs in the hormone level, and best represents the “steady state” level produced from the last dose.
In general, testing should be done approximately half way between dosages.
- For a testosterone injection given every 2 weeks, testing should be done approximately one week after the last injection.
- For a topical hormone cream or gel applied once daily, testing should be done approximately 12 hours after the last application.
- If the topical cream or gel is used twice a day or every 12 hours, testing should be done approximately 6 hours after the last application.
- For oral Slow Release compounded capsules, testing should be done 4 to 8 hours after the last dose.
Exceptions do occur where these general guidelines do not necessarily apply. Based on pharmacokinetics, sublingual troches should be dosed at least 3 times a day, but are most often administered only twice a day. Hormone levels from sublingual troches and drops return to baseline in about 6 hours, so testing should be done about 4 hours after the last dose.
If you employ a lab that has determined expected ranges for 12-24 hours after a dose of cream or oral, then the above guidelines do not have to be followed. But always keep in mind the relationship of the timing of the last dose and the frequency of dosing when interpreting the test results.
For example: If a female patient is applying the estrogen cream once daily in the morning, and she collects her saliva for testing first thing in the morning before she applies her dose, consider that she is at the end of her dosing interval at the time of testing. If her estrogen levels are at the high end of the normal range at that time, then her levels during most of the dosing interval would be high. Or she may be slightly low in her estrogen at the time of testing, but slightly low or low normal would be a good level for the end of the dosing interval. Always correlate the level to symptoms that she may or may not experiencing also.
Timing of thyroid testing is based on the duration of the thyroid hormone or hormones that are being administered.
If a patient taking thyroid medication once daily in the morning has not taken their medication before sampling on the day of testing, then at least 24 hours has passed since they last took their medication. The thyroid hormone levels would not represent those caused as a result of therapy, but more of the endogenous baseline production from the thyroid gland.
With immediate released thyroid products (all manufactured products are IR):
- IR T4 peaks in most individuals in 2-4 hours. Levels of T4 drop back to baseline in approximately 18-20 hours after the dose. Therefore the best time to test levels for a patient on an IR T4 product is 4 to 18 hours after the last dose.
- IR T3 peaks in 1-2 hours, and returns to baseline in 4-6 hours. The best time to test for a patient taking an IR T3 product is 2-4 hours after the last dose.
- For combination IR T4 and T3 products, including desiccated porcine thyroid products, the best time to test is 4 hours after the last dose of medication. Testing any sooner than 4 hour post dose can result in a peak of T4; testing any later than 4 hours post dose can result in a drop off in the T3 level.
For compounded Slow Released T4, T3, or combination preparations, testing should be done 4 to 8 hours after the last dose.
It may be helpful to note that with all thyroid medications, testing can be done 4 hours after the last dose!
When you test thyroid depends on what you wish to look at. For levels resulting from therapy, use the above guidelines. If you wish to look at levels resulting from endogenous production, then have the patient not take their medication for at least 24 hours prior to testing. I only wish insurance companies could understand why I would want to test first thing in the morning (before any medication) and then repeat the tests again 4 hours after the medication!
For all hormone testing, it is important to keep the timing of the last dose vs. the timing of the sampling consistent with follow up testing.
Related: This Symptom Checklist Can Help You Determine a Hormone Testing Method
Jim Paoletti, BS Pharmacy, FAARFM, FIACP, is the Director of Education at Power2Practice and a Clinical Consultant with over 30 years’ experience creating and using bio-identical hormone therapies in both retail pharmacy and clinical practice.
Jim is a Diplomat in Functional Medicine in addition to being a former faculty member for the Fellowship of Functional Medicine. Jim also authored the book, “A Practitioner’s Guide to Physiologic Bioidentical Hormone Balance,” which is available on Amazon.
At Power2Practice, Jim applies his wealth of knowledge and experience by hosting live webinars and creating useful content, such as blogs, podcasts and clinical support tools.