What do the results of my thyroid test mean?

Understanding TSH test results
on Mon 7 Dec


Blood tests are currently the most accurate way in which to diagnose and manage thyroid disorders.


When a GP suggests a thyroid function test they are looking at the thyroid hormone levels in your bloodstream and comparing them to reference ranges (or levels) in 95% of the healthy population.


Looking at TSH

Whether you wonder if you have hypothyroidism because you have gone to the doctor with symptoms listed in this blog post


 You’ve gone because you think you might have hyperthyroidism because you have some of the symptoms listed on this patient information sheet


The doctor will diagnose your condition with the aid of a test looking at your Thyroid Stimulating Hormone (TSH) which is a hormone produced by the pituitary gland in response to your thyroid hormone production. The pituitary gland is very sensitive and acts as a regulator telling your thyroid gland to increase or decrease T4 and T3 production according their levels in the bloodstream.


Hypothyroidism will be suspected if the TSH level is high and Hyperthyroidism will be suspected if your TSH level is low due to negative feedback. As your levels of thyroid hormone (T4 and T3) fall, the serum TSH rises. As your levels of T4 and T3 rise the serum TSH falls.


TSH levels have been standardised internationally and vary according to your age and gender. Examples of suggested reference ranges and the normal, low and high TSH levels are shown below:









0.5-4.15 mIU/L

<0.5 mIU/L

>4.5 mIU/L



0.5-4.15 mIU/L

<0.5 mIU/L

>4.15 mIU/L



0.5-4.59 mIU/L

<0.5 mIU/L

>4.6 mIU/L



0.4-5.49 mIU/L

<0.4 mIU/L

>5.5 mIU/L



0.4-2.34 mIU/L

<0.4 mIU/L

>4.5 mIU/L



0.4-4.0 mIU/L

<0.4 mIU/L

>4.1 mIU/L



0.46-4.68 mIU/L

<0.46 mIU/L

4.7-7.0 mIU/L


*mlUI/L stands for milli international units per litre


During pregnancy a mother’s TSH levels will alter as they are affected by hormones secreted at that time. This creates these levels.





First Trimester

0.2-2.5 mIU/L

<0.2 mIU/L

2.5-10 mIU/L

Second Trimester

0.3-3.0 mIU/L

<0.3 mIU/L

3.01-4.50 mIU/L

Third Trimester

0.8-5.2 mIU/L

<0.8 mIU/L

>5.3 mIU/L


It is important for your TSH levels to be checked both before deciding to become pregnant AND during the pregnancy as both hyperthyroidism and hypothyroidism can occur at this time. Left untreated this can cause health problems for both yourself and the baby.


People with Addison’s disease, Turner Syndrome or Down’s syndrome should also be tested regularly as should those with other autoimmune diseases


Looking at T4 and T3

In response to TSH your thyroid gland will make two forms of T3 and T4. If it is referred to as “bound” it means it is attached to a protein. 99% of T4 is bound. In most cases now it is the free T4 and T3 levels that are measured. Typical results for free T4 and free T3 are as follows:


  • Free T4 12-20 pmol/l
  • Free T3 3-7pmol/l


Looking at confusing results

If TSH levels are low  one would expect to see high levels of T3 and T4.  If TSH levels are high one would expect to see low levels of T3 and T4


The table below highlights the common patterns:


However in some cases the results do not present this anticipated pattern. These are discussed in an excellent review by the Cambridge Thyroid Group which run the national reference laboratory for “weird” thyroid function tests:

Olympia Koulouri , Carla Moran, David Halsall, Krishna Chatterjee, Mark Gurnell. Pitfalls in the measurement and interpretation of thyroid function tests. Best Pract Res Clin Endocrinol Metab 2013 27:745-62. doi: 10.1016/j.beem.2013.10.003. Epub 2013 Oct 17.


This includes this most useful diagram


*NTI = non-thyroidal illness

*FDH = familial dysalbuminaemic hyperthyroxinaemia

*FT3 = free triiodothyronine  

*FT4  = free thyroxine

*TSH = thyroid-stimulating hormone (thyrotropin)


I hope this has been helpful.


Although every effort is made to ensure that all health advice on this website is accurate and up to date it is for information purposes and should not replace a visit to your doctor or health care professional.


As the advice is general in nature rather than specific to individuals Dr Vanderpump cannot accept any liability for actions arising from its use nor can he be held responsible for the content of any pages referenced by an external link


acanthosis nigricans Acromegaly Addison's disease adolescent diabetes problems adolescent thyroid problems Adrenal crisis adrenal fatigue Adrenal glands Anovulation artificial pancreas Autoimmune Thyroiditis Bariatric Surgery blood glucose levels blood pressure breastfeeding CAH Charcot foot cholesterol CHT coffee cold and flu medications Conception Congenital adrenal hyperplasia congenital hypothyroidism Consultant Endocrinologist London coronavirus cortisol covid-19 Cushing's disease Cushing's syndrome Depression Diabetes diabetes and bone health diabetes and heart health diabetes and oral health diabetes and parkinsons diabetes and sexual dysfunction diabetes and skin conditions diabetes and thrush diabetes in China diabetes insipidus diabetes latest diabetic ketoacidosis diabetic neuropathy Diabetic prevalence diabetic retinopathy diet for diabetes diet for obesity Disability Act Down's Syndrome Dr Mark Vanderpump e-consulting endocrine system fertility folic acid Freestyle Libre frozen shoulder and thyroid Fruit sugars gestational diabetes Gigantism Glucose Monitoring Glucose Tolerance Test gluten free Goitre Graves Disease Graves Orbitopathy guthrie test hair loss Hashimoto's Disease healthcare services hearing loss Heart Disease heel prick test Hepatitis C Hormones - most important how to lose weight hyperparathyroidism Hypersecretion Hyperthyroidism hyperthyroidism and respiratory problems Hypocalcaemia Hypogonadism hypoparathyroidism hypophysitis Hyposecretion Hypothyroidism hypothyroidism and respiratory problems IFG IGT immunotherapy side effects Impaired Fasting Glucose Impaired Glucose Tolerance Insulin Resistance Iodine IR iron Labour and birth late onset hypogonadism Levothyroxine Long Covid losing weight Low testosterone Mark Vanderpump MEN1 MEN2 menopause metabolic syndrome mood changes morning sickness Multiple endocrine neoplasia neuroendocrine tumour neuropathy Obesity obstructive sleep apnoea older patients online doctor OSA Osteoporosis overactive thyroid ozempic Pancreas Pancreatic Cancer Pancreatic Diabetes parathyroid glands Patient Resources Patient Support Groups PCOS PCOS and acne PCOS and fertility PCOS and Insulin PCOS diet Phaeochromocytomas Pituitary Gland POF Polycystic Ovary Syndrome Post menopause thyroid problem Post pregnancy thyroid problem postnatal diabetes medication postnatal thyroid medication Prader-Willi Syndrome pre-eclampsia prediabetes pregnancy Pregnancy and Diabetes Pregnancy and Thyroid Disease Premature Ovarian Failure prolactinomas PTH puberty Radioactive Iodine RAI resistant hypertension semaglutide Sheehan's Syndrome Skin tags sleep and diabetes sleep and obesity soy Soya steroid dependent subacute thyroiditis T4 Tara Palmer Tomkinson testosterone Tetany The endocrine system Thyroid thyroid and menstruation thyroid cancer Thyroid disease in children thyroid nodules Thyroid Storm thyroid tests Thyroiditis Thyrotoxic Periodic Paralysis Thyroxine TSH levels TSH Testing tumours Type 1 diabetes Type 2 Diabetes Type 3 diabetes underactive thyroid Vitamin B complex Vitamin D Waist circumference weight gain weightloss

Please get in touch

Phone: 07565 978310

Contact form