How to prepare for your test | Stoltman range | IMULAB
Stoltman range  /  Before you test

Getting your blood sample instructions

Time of day, recent training, food and certain supplements all alter blood results. Answer the questions below and you will get the preparation steps that apply to your test.

Two minutes

Tell us a bit about you

Who is the test for?
Where are you in your cycle?
This panel measures hormones that change across the cycle, so the day you test affects how your results are read.
Anything you are taking?
Tap all that apply. Do not stop anything, we just need to know.

Your prep plan

Showing the standard plan
A week before

Check your labels for biotin

Biotin appears in hair, skin and nail supplements, greens powders, pre workout and energy drinks. At 5mg or more, stop a week before. A standard multivitamin needs 48 to 72 hours.

You said you take biotin

Stop it today if you are on a high dose. Restart the morning after your sample. Dietary biotin from eggs, salmon and nuts is thousands of times lower than supplement doses and does not need to be avoided.

Why this matters
Most hormone assays rely on a biotin and streptavidin binding step. Circulating biotin from a supplement competes with the reagent and distorts the result. The typical pattern is a falsely low TSH alongside a falsely high free T4 and free T3, which reads as an overactive thyroid in someone with normal thyroid function. Testosterone, vitamin D and cortisol assays can be affected in the same way.
48 to 72 hours before

Last heavy session

Leave 48 hours after hard lifting. Leave 72 after a competition, a max effort day, or heavy eccentric work your body is not conditioned to. Walking and mobility work are fine up to the morning of the test.

Why this matters
Loading skeletal muscle releases CK, AST, ALT and LDH into circulation, and raises urea, creatinine, uric acid, potassium and white cell count. In one study of previously untrained men, every participant showed elevated AST and ALT after a single one hour resistance session, and all markers of muscle damage remained elevated for at least seven days. Trained lifters show a smaller rise, but the effect is still present. Without knowing about the session, elevated AST and ALT reads as liver dysfunction rather than muscle damage.

If 48 hours is not possible, test anyway and record what you trained and when. Then test at the same point in your training week each time so your retests are comparable.
The day before

No alcohol

Avoid alcohol for the full 24 hours before your sample. A single evening is enough to raise GGT and triglycerides.

You said you take iron

Leave at least 24 hours between your last iron tablet and the sample. Oral iron raises serum iron sharply for several hours after a dose, which overstates your iron status.

The night before

Stop eating, keep drinking water

Aim for 10 to 12 hours without food. Water is fine and helps. No coffee, no tea, no milk, no juice, no sweets or sugared gum.

Why this matters
Glucose and insulin are only interpretable in the fasted state. Lipids change less after eating than is commonly assumed, so a non fasted cholesterol panel remains usable, but fasting removes the variable entirely and keeps every retest comparable. Adequate hydration also makes the draw easier and prevents mild dehydration concentrating your results.

If you are diabetic, or on medication that makes fasting unsafe, do not fast. Email us first and we will work around it.
Test morning

Sample between 7am and 10am

Book the earliest appointment you can get. Drink water before you go, it makes the vein easier to locate.

You said you take thyroid medication

Take it after the draw, not before. Free T4 peaks two to four hours after a levothyroxine dose, so a tablet at 7am and a sample at 9am produces a free T4 reading higher than your level for the remaining 22 hours of the day. Bring it with you and take it immediately afterwards.

You said you are on TRT or hormone therapy

Stay on your protocol. Record the product, the dose and exactly when you last took it. Where the sample falls within your injection, gel or patch cycle determines what the result represents.

Why this matters
Testosterone follows a diurnal rhythm, peaking in the early morning and declining through the day. In men under 45 the difference between an 8am and an afternoon reading is large enough to return a falsely low result. TSH and cortisol follow their own morning patterns. When you retest, aim for the same hour so the comparison holds.
At your appointment

Venous draw

This panel requires a venous sample taken by a healthcare professional. Wear a top with a sleeve that rolls above the elbow, and bring your paperwork exactly as it was sent. If you are prone to feeling faint, say so before you sit down and stay seated for a few minutes afterwards.

Choosing the day

Book Monday to Thursday

Blood is a perishable sample. A Friday draw risks the sample sitting in transit over the weekend, which is the most common reason a test is rejected and has to be repeated. Treat the day before a bank holiday the same way.

Mon
Tue
Wed
Thu
Fri
Sat
Sun
If you are sending the sample yourself
If your sample is being taken by your own healthcare professional rather than at a clinic or by one of our nurses, post it the same day it is drawn. Use a priority postbox where there is one and check the collection time on the plate before you post. Do not hold the sample overnight, and do not refrigerate or freeze it.
Cycle timing

Timing your test to your cycle

Test on day 2 to 5. Day 1 is the first day of full bleeding, not spotting, so if your period starts on a Monday your window runs Tuesday to Friday. Aim for a weekday inside it.

1
2
3
4
5
6
7

Day 1 = first day of full flow

This is the early follicular phase, when FSH, LH and oestradiol are at a stable baseline. Research comparing individual days across days 2 to 5 found no clinically significant difference between them, so anywhere in that window is valid. If your window has already passed this month, wait for your next period rather than testing outside it.

Record your cycle day when you register your sample. Without it, hormone results cannot be interpreted properly.

Test on any day. Without a predictable cycle there is no reliable window to aim for, so book whenever suits and follow the morning and fasting steps as normal.

Record the date your last period started, or note that you have not had one. Irregular or absent cycles are themselves clinically relevant, particularly in athletes carrying a high training load, and the pattern is often more informative than the individual numbers. If your cycle has stopped or become irregular since increasing your training volume, tell us, it changes what we look for.

Test on any day, and keep taking it.

Hormonal contraception suppresses your own FSH, LH and oestradiol, and combined pills raise SHBG, which lowers free testosterone. Your results describe your hormones on contraception rather than your underlying baseline. That is still useful, but it has to be read in context, so record the type, the brand and where you are in the pack or cycle.

Test on any day. Cycle timing no longer applies, so book whenever suits.

If you are on HRT, stay on it and record the type, the dose and when you last took it. Transdermal and oral routes affect SHBG differently, which changes how your hormone results are read.

The rest of your panel is unaffected by cycle day. Cycle timing only changes how the hormone markers are interpreted.

The rest of it

Things people ask us

I am unwell, should I still test?

No, wait until you have recovered. Do not test with a fever or an active infection, and leave around two weeks after a significant illness before you book.

CRP rises within hours of an infection starting. Ferritin rises behind it and stays elevated for weeks, while serum iron falls. A sample taken in that window describes the infection rather than your baseline. The same applies in the fortnight after surgery, a vaccination, or a course of antibiotics.

A mild head cold with no fever is usually fine. Record it when you register your sample.

Does creatine affect my results?

It can have an effect on one marker.

Creatine is metabolised to creatinine, so supplementing raises serum creatinine. Because eGFR is calculated from creatinine, eGFR then falls. That reads as reduced kidney function when kidney function is more often than not normal, there is simply more creatinine in circulation.

Keep taking it. Record the dose and whether you are loading, and your results will be read accordingly.

Do I need to stop my prescribed medication?

No. Statins, blood pressure medication, contraception, antidepressants, thyroid medication and steroids should all be taken exactly as prescribed.

Only your prescriber should change a prescription, and never for the purpose of a blood test.

The one timing point worth following is thyroid medication, which should be taken after the draw rather than before.

What about my other supplements?
  • Vitamin D, omega 3, magnesium, protein and collagen: continue as normal
  • Biotin: pause, see the plan above
  • Iron: leave 24 hours after your last dose
  • Anything started in the last month: record it, as it may not be reflected in your bloods yet

If you are testing to find out whether a supplement is working, you can continue to take it.

The night before

Quick check

  • Last food eaten, water only from here
  • No alcohol in the last 24 hours
  • 48 hours since your last heavy session
  • Biotin paused
  • Iron paused for 24 hours
  • Thyroid tablet set aside to take after the draw
  • Appointment confirmed for between 7am and 10am
  • Sleeve that rolls above the elbow
Where this guidance comes from
  1. Nordestgaard BG, Langsted A, Mora S, et al. Fasting is not routinely required for determination of a lipid profile: a joint consensus statement from the European Atherosclerosis Society and the European Federation of Clinical Chemistry and Laboratory Medicine. Eur Heart J. 2016;37(25):1944 to 1958.
  2. Nordestgaard BG. A test in context: lipid profile, fasting versus nonfasting. J Am Coll Cardiol. 2017;70(13):1637 to 1646.
  3. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715 to 1744.
  4. Brambilla DJ, Matsumoto AM, Araujo AB, McKinlay JB. The effect of diurnal variation on clinical measurement of serum testosterone and other sex hormone levels in men. J Clin Endocrinol Metab. 2009;94(3):907 to 913.
  5. Welliver RC, Wiser HJ, Brannigan RE, et al. Validity of midday total testosterone levels in older men with erectile dysfunction. J Urol. 2014;192(1):165 to 169.
  6. Pettersson J, Hindorf U, Persson P, et al. Muscular exercise can cause highly pathological liver function tests in healthy men. Br J Clin Pharmacol. 2008;65(2):253 to 259.
  7. Thomas L. Effect of physical exercise on laboratory test results. Clinical Laboratory Diagnostics, chapter 51.
  8. Kratz A, Lewandrowski KB, Siegel AJ, et al. Effect of marathon running on hematologic and biochemical laboratory parameters. Am J Clin Pathol. 2002;118(6):856 to 863.
  9. Avery G. Biotin interference in immunoassay: a review for the laboratory scientist. Ann Clin Biochem. 2019;56(4):424 to 430.
  10. Piketty ML, Prie D, Sedel F, et al. High dose biotin therapy leading to false biochemical endocrine profiles. Clin Chem Lab Med. 2017;55(6):817 to 825.
  11. World Health Organization. Guideline on the prevention, diagnosis and treatment of infertility, 2025. Day 2 to 3 FSH, AMH and antral follicle count for ovarian reserve.
  12. Namaste SM, Rohner F, Huang J, et al. Adjusting ferritin concentrations for inflammation: BRINDA project. Am J Clin Nutr. 2017;106(Suppl 1):359S to 371S.
  13. Ain KB, Pucino F, Shiver TM, Banks SM. Thyroid hormone levels affected by time of blood sampling in thyroxine treated patients. Thyroid. 1993;3(2):81 to 85.
  14. Post A, Tsikas D, Bakker SJL. Creatine is a conditionally essential nutrient: effects of supplementation on serum creatinine and estimated GFR. Nutrients. 2019;11(5):1044.
  15. Wiegratz I, Kutschera E, Lee JH, et al. Effect of four oral contraceptives on thyroid hormones, adrenal and blood pressure parameters, and sex hormone binding globulin. Contraception. 2003;67(5):361 to 366.

Ask us

If something here does not fit your situation, if you are unsure whether to test this week, or if you need further advice email us.

support@imulab.co

Know. Act. Become.

This page explains how to collect a sample that reflects your usual physiology. It is general guidance, not medical advice, and it does not replace the advice of your doctor. Never stop or change a prescribed medication in order to take a blood test. If you feel unwell, speak to your GP or call 111.