Your GP checks TSH. If it is normal, you are told your thyroid is fine. But TSH is one marker in a system that needs four. Here is what a proper thyroid blood test should include, what each marker reveals, and why millions of people with thyroid symptoms are told nothing is wrong.
Your thyroid controls metabolic rate, energy production, body temperature, weight regulation, mood, heart rate, and cognitive function. Testing it properly requires four markers, not one.
| Marker | What It Is | What It Reveals | Who Tests It |
|---|---|---|---|
| TSH | Thyroid-stimulating hormone from the pituitary gland | How hard your brain is working to stimulate your thyroid. High TSH = underactive. Low TSH = overactive. But a "normal" TSH does not guarantee optimal function. | NHS, most private providers, TrueVitals |
| Free T4 | Inactive thyroid hormone produced by the thyroid gland | How much hormone your thyroid is producing. T4 must be converted to T3 to become active. Normal T4 with low T3 indicates a conversion problem. | NHS (sometimes), some private providers, TrueVitals |
| Free T3 | Active thyroid hormone that drives metabolic rate | The hormone your cells actually use. This is what determines how you feel. Low Free T3 causes fatigue, weight gain, cold intolerance, and brain fog regardless of what TSH says. | Rarely NHS, rarely private providers, TrueVitals (every panel) |
| Thyroid antibodies (TPO/TG) | Immune system proteins that attack thyroid tissue | Detects autoimmune thyroid disease (Hashimoto's, Graves'). Can be elevated years before TSH shifts. The earliest warning of thyroid autoimmunity. | Rarely NHS (only if TSH abnormal), rarely private, TrueVitals (every panel) |
Your thyroid produces T4 (inactive). Your body converts T4 to T3 (active) in the liver, gut, and peripheral tissues. If conversion is impaired, your TSH stays normal (the pituitary sees enough T4) but Free T3 is low. You experience all the symptoms of an underactive thyroid: fatigue, weight gain, cold hands and feet, brain fog, constipation, low mood, hair thinning. Your GP tests TSH, sees a normal result, and tells you your thyroid is fine. Without Free T3, the conversion problem is invisible.
Common causes of poor conversion include chronic stress (elevated cortisol), calorie restriction, iron deficiency, selenium deficiency, gut dysfunction, and chronic inflammation. All of which a comprehensive blood test can identify.
Hashimoto's thyroiditis is the most common cause of hypothyroidism in the UK. The immune system produces antibodies (TPO antibodies and thyroglobulin antibodies) that gradually attack and destroy thyroid tissue. This process can continue for years, even decades, before TSH becomes abnormal. During this time, you may have fluctuating symptoms, but every TSH test comes back "normal."
Testing thyroid antibodies catches Hashimoto's at the autoimmune stage, before permanent thyroid damage occurs. Early detection opens a window for dietary and lifestyle interventions (gluten elimination, selenium supplementation, stress reduction) that can slow or stabilise the autoimmune process. By the time TSH is high, thyroid tissue has already been significantly destroyed.
The NHS TSH reference range is typically 0.27 to 4.2 mU/L. That is a very wide range. A TSH of 0.8 and a TSH of 3.8 are both "normal" but represent very different states of thyroid function. Research suggests optimal TSH sits between 0.5 and 2.0 for most people. A TSH of 3.5 is not clinically hypothyroid, but it may represent suboptimal function causing fatigue, weight gain, and low mood that a standard test would never flag.
TrueVitals highlights suboptimal results, not just clinically abnormal ones. Your report shows where your TSH, Free T3, and Free T4 sit relative to the optimal range, not just the reference range. This is the difference between being told "your thyroid is fine" and being told "your thyroid is technically in range but below the level associated with feeling your best."
The classic hypothyroid symptoms (fatigue, weight gain, cold intolerance) are well known. But thyroid dysfunction also affects systems people rarely attribute to it.
Hypothyroidism raises LDL cholesterol by slowing hepatic LDL receptor clearance. Many people are prescribed statins for "high cholesterol" that is actually being driven by an underactive thyroid. Treating the thyroid normalises the cholesterol without medication.
Subclinical hypothyroidism affects ovulation, implantation, and increases miscarriage risk. Thyroid antibodies are associated with recurrent pregnancy loss even when TSH appears normal. Full thyroid testing is essential for anyone trying to conceive.
Low Free T3 directly affects brain function. It slows processing speed, impairs memory, and contributes to depression and anxiety. Thyroid dysfunction is one of the most commonly missed contributors to mood disorders.
Thyroid dysfunction causes hair thinning, brittle nails, dry skin, and puffiness, particularly around the eyes and face. These changes are gradual and often attributed to ageing rather than a treatable hormonal issue.
| Provider | TSH | Free T4 | Free T3 | Antibodies |
|---|---|---|---|---|
| NHS (GP request) | Yes | Sometimes | Rarely | Only if TSH abnormal |
| Medichecks (comprehensive) | Yes | Yes | Not in standard panels | Not in standard panels |
| Thriva | Yes | Not in standard | No | No |
| Forth | Yes | Some panels | No | No |
| Lola Health | Yes | Yes | Not standard | Not standard |
| TrueVitals (all panels) | Yes | Yes | Yes | Yes |
TrueVitals is the only UK provider that includes Free T3 and thyroid antibodies as standard in every panel, from Advanced to Signature. Most providers only test TSH, or TSH with Free T4. See our full provider comparison.
Your thyroid does not operate independently. Iron deficiency impairs thyroid hormone production. Cortisol affects T4-to-T3 conversion. Insulin resistance alters thyroid-binding proteins. Vitamin D deficiency is associated with higher rates of autoimmune thyroid disease. Selenium is essential for the enzyme that converts T4 to T3.
A standalone thyroid test gives you four markers without context. A TrueVitals Ultimate panel gives you those same four markers alongside iron studies, cortisol, insulin, vitamin D, selenium (via glutathione reductase), and 100+ other markers. Your AI-powered report cross-references all of them and identifies which systems are influencing your thyroid function.
If your Free T3 is low, the report does not just flag it. It tells you whether iron, cortisol, caloric intake, or inflammation might be driving the conversion problem, and gives you specific recommendations. See how our reports work.
TSH, Free T3, Free T4, and thyroid antibodies (TPO and TG). TSH alone misses conversion problems and early autoimmune thyroid disease. TrueVitals includes all four in every panel from Advanced (£269) onwards.
NHS guidelines use TSH as a first-line screening marker. If TSH is normal, further testing is generally not commissioned under standard protocols. This is a cost and protocol issue, not a clinical best-practice issue. Many endocrinologists recommend the full panel for symptomatic patients. NHS vs private testing compared.
Yes. TPO antibodies and thyroglobulin antibodies detect autoimmune thyroid disease. They can be elevated for years before TSH becomes abnormal, making them the earliest marker of Hashimoto's. TrueVitals tests both in every panel.
The reference range is typically 0.27 to 4.2 mU/L. Optimal is generally 0.5 to 2.0 mU/L. A TSH above 2.5 with symptoms (fatigue, weight gain, cold intolerance) is worth investigating further with Free T3, Free T4, and antibodies. Your TrueVitals report highlights both the reference and optimal ranges.
If you take levothyroxine, take your blood test before your morning dose. Taking it before the test can falsely elevate Free T4. If you take T3 (liothyronine), test 12 hours after your last dose. Tell us what medication you take in your lifestyle quiz so your report adjusts interpretation accordingly.
TSH, Free T3, Free T4, and antibodies included as standard. Plus 110+ other markers for the complete context. From £269.
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