Blood test prep

[ZM1980]

Hello all, quick question re Thyroid blood test: do I need to fast for this? The test also includes cortisol. Will be booking an early a. m. appointment, as I know this is recommended. Thank you 🙂

[SeasideSusie Remembering]

ZM1980

This is what we advise when having thyroid tests:

* Book the first appointment of the morning, or with private tests at home no later than 9am. This is because TSH is highest early morning and lowers throughout the day.

In fact, 9am is the perfect time, see first graph here, it shows TSH is highest around midnight - 4am (when we can't get a blood draw), then lowers, next high is at 9am then lowers before it starts it's climb again about 9pm:

healthunlocked.com/thyroidu...

If we are looking for a diagnosis of hypothyroidism, or looking for an increase in dose or to avoid a reduction then we need TSH to be as high as possible.

* Nothing to eat or drink except water before the test - have your evening meal/supper as normal the night before but delay breakfast on the day of the test and drink water only until after the blood draw. Certain foods may lower TSH, caffeine containing drinks affect TSH.

* If taking thyroid hormone replacement, last dose of Levo should be 24 hours before blood draw. If taking NDT or T3 then last dose should be 8-12 hours before blood draw, split dose and adjust timing the day before if necessary. This avoids measuring hormone levels at their peak after ingestion of hormone replacement. Take your thyroid meds after the blood draw. Taking your dose too close to the blood draw will give false high results, leaving any longer gap will give false low results.

* If you take Biotin or a B Complex containing Biotin (B7), leave this off for 3-7 days before any blood test. This is because if Biotin is used in the testing procedure it can give false results (most labs use biotin).

These are patient to patient tips which we don't discuss with phlebotomists or doctors.

[ZM1980 in reply to SeasideSusie]

Thanks SeasideSusie, useful info. I think Superdrug clinics have earliest appointment at 9.30am, so will book for this time. Interesting about the TSH levels varying throughout the day/night. My energy levels and symptoms improve towards the evening, so a blood test around midnight would actually be ideal, (although obviously not an option)! I do take a vitamin B complex, so will stop this prior to the test (as well as Zinc, vitamin D, Ferrous Fumerate).