When you receive your thyroid blood test results, they can look like a confusing alphabet soup of acronyms: TSH, T4, T3, Free T3, Free T4, TPO, TG, rT3. What do all mean? And more importantly, what do your results tell you about your thyroid health? Understanding your thyroid function test results is crucial because thyroid hormones affect virtually every cell in your body. They control your metabolism, energy levels, body temperature, heart rate, mood, weight, and so much more. This comprehensive guide will walk you through every marker on a complete TFT blood test, explaining in plain English what each one measures, what ‘normal’ really means, and what your results indicate about your thyroid health.
What Is Thyroid Function Testing?
A thyroid function blood test (often abbreviated as TFT) is a group of blood tests used to measure how well your thyroid gland is working. Your thyroid is a small, butterfly-shaped gland in your neck that produces hormones regulating your metabolism. The blood sample fora thyroid test is typically taken from a vein in your arm, just like any standard blood test. The sample is then sent to a laboratory where various thyroid markers are measured.
Why Thyroid Testing Matters
Your thyroid produces two main hormones:
- T4 (thyroxine) – the storage form of thyroid hormone
- T3 (triiodothyronine) – the active form that does the actual work in your cells
When your thyroid doesn’t produce enough hormones (hypothyroidism) or produces too much (hyperthyroidism), it can cause a wide range of symptoms affecting your energy, weight, mood, heart, digestive system, and more.
TSH (Thyroid Stimulating Hormone)
What TSH Measures
TSH isn’t actually a thyroid hormone; it’s produced by your pituitary gland in your brain. Think of TSH as your body’s thermostat for thyroid function. When thyroid hormone levels drop too low, your pituitary gland releases more TSH to signal your thyroid to produce more hormones. When thyroid hormone levels are adequate, TSH production decreases. It’s a feedback loop.TSH Reference Ranges
Standard Australian lab range: 0.5 to 4.0 mIU/L (varies slightly between labs) Optimal functional range: 1.0 to 2.0 mIU/LWhat Your TSH Results Mean
High TSH (above 4.0): Suggests hypothyroidism (underactive thyroid). Your pituitary is working overtime trying to stimulate your thyroid to produce more hormones. Low TSH (below 0.5): Suggests hyperthyroidism (overactive thyroid). Your thyroid is producing too much hormone, so your pituitary has stopped sending stimulation signals. Normal but high-normal TSH (2.5-4.0): You’re technically within ‘normal range,’ but many people with TSH in this range still have symptoms. This is where comprehensive testing becomes important. If you have a normal TSH but still feel unwell: What to Do If Your TFT Is Normal But You Still Have SymptomsT4 (Thyroxine) - The Storage Hormone
What T4 Measures
T4 is the main hormone your thyroid produces, making up about 80% of thyroid hormone output. It’s called the ‘storage’ form because it needs to be converted into T3 (the active form) before your body can use it.
There are two types of T4 measurements:
- Total T4: Measures all T4 in your blood, both bound to proteins and unbound
- Free T4: Measures only the unbound T4 that’s available for your body to use
Free T4 is more clinically useful because it represents the hormone that’s actually available to your cells.
Free T4 Reference Ranges
Standard Australian lab range: 10-20 pmol/L (varies between labs)
Optimal functional range: Middle to upper third of the range (approximately 14-18 pmol/L)
What Your Free T4 Results Mean
Low Free T4: Indicates your thyroid isn’t producing enough hormone. This confirms hypothyroidism when combined with high TSH.
High Free T4: Suggests your thyroid is producing too much hormone, indicating hyperthyroidism.
Normal Free T4 with high TSH: This is called subclinical hypothyroidism — your thyroid is still producing hormone, but your body is signalling it needs more.
T3 (Triiodothyronine) - The Active Hormone
What T3 Measures
T3 is the active thyroid hormone — it’s what actually does the work in your cells. About 80% of your T3 comes from the conversion of T4 in your liver, kidneys, gut, and other tissues. Only about 20% is produced directly by your thyroid. Like T4, T3 can be measured as:- Total T3: All T3 in your blood
- Free T3: The unbound, active T3 available to your cells
Why T3 Testing Is Often Missed (But Crucial)
Here’s a critical point: many standard thyroid gland tests don’t include Free T3. GPs typically only order TSH, and sometimes Free T4. This is problematic because you can have:- Normal TSH
- Normal Free T4
- BUT low Free T3 (poor conversion)
Free T3 Reference Ranges
Standard Australian lab range: 3.5-6.5 pmol/L (varies between labs) Optimal functional range: Upper third of the range (approximately 5.0-6.5 pmol/L)What Your Free T3 Results Mean
Low Free T3: Suggests either your thyroid isn’t producing enough T3, or your body isn’t converting T4 to T3 properly. Common causes include stress, inflammation, nutrient deficiencies, and liver problems. High Free T3: May indicate hyperthyroidism, or in some cases, overmedication with thyroid hormone. Normal T4 but low T3: This pattern points to a conversion problem. Your thyroid is producing hormone, but your body isn’t activating it properly. Learn more about conversion issues: Low T3 Syndrome: What Is It and Do You Have It?Reverse T3 (rT3) - The Thyroid Brake
What Is Reverse T3?
Reverse T3 is a mirror image of T3 that’s biologically inactive. When your body converts T4, it can go two ways:- Active T3 (speeds up metabolism)
- Reverse T3 (blocks thyroid receptors, slowing metabolism)
Why Reverse T3 Testing Matters
Elevated reverse T3 can explain why people have thyroid symptoms despite normal TSH, T4, and even T3. The thyroid hormones are there, but reverse T3 is blocking them from working. Common causes of elevated reverse T3:- Chronic stress
- Chronic illness or inflammation
- Calorie restriction or yo-yo dieting
- Liver or kidney dysfunction
- Certain medications (beta-blockers, oral contraceptives)
- Diabetes
- Ageing
Reverse T3 Reference Ranges
Standard lab range: 0.14-0.54 nmol/L Optimal range: Lower third of range (< 0.30 nmol/L) More important than the absolute value is the Free T3 to Reverse T3 ratio. A healthy ratio is above 20 (when both measured in the same units). Dive deeper into our guide on Understanding Reverse T3 and Why It MattersThyroid Antibodies - Detecting Autoimmune Disease
What Are Thyroid Antibodies?
Thyroid antibodies are proteins your immune system produces when it mistakenly attacks your thyroid gland. Elevated antibodies indicate autoimmune thyroid disease, most commonly Hashimoto’s thyroiditis.
The two main thyroid antibodies tested are:
1. TPO Antibodies (Anti-Thyroid Peroxidase)
TPO is an enzyme crucial for thyroid hormone production. TPO antibodies attack this enzyme, interfering with your thyroid’s ability to produce hormones.
Reference range: Less than 35 IU/mL (ideally less than 9 IU/mL)
What elevated TPO means: You have or are at risk of developing Hashimoto’s thyroiditis, even if your thyroid function tests are currently normal.
2. TG Antibodies (Anti-Thyroglobulin)
Thyroglobulin is a protein used by your thyroid to make thyroid hormones. TG antibodies attack this protein.
Reference range: Less than 115 IU/mL (ideally less than 40 IU/mL)
What elevated TG means: Often seen alongside TPO antibodies in Hashimoto’s. Some people only have elevated TG antibodies.
Why Antibody Testing Is Crucial
Here’s the problem: you can have elevated thyroid antibodies for years — even decades — before they significantly affect your TSH or thyroid hormone levels. During this time, you may experience:
- Fluctuating energy levels
- Weight gain
- Hair loss
- Brain fog
- Mood changes
Without antibody testing, Hashimoto’s goes undiagnosed, and you miss the opportunity for early intervention to slow disease progression. Learn more: Thyroid Antibodies: Autoimmune Thyroid Disease
How to Read Your Thyroid Blood Test Results
Understanding the relationship between different thyroid markers is key to interpreting your results. Here are common patterns and what they mean:
Pattern 1: Primary Hypothyroidism
- High TSH
- Low Free T4
- Low Free T3
What this means: Your thyroid isn’t producing enough hormone. This is classic hypothyroidism and typically requires thyroid hormone replacement.
Pattern 2: Subclinical Hypothyroidism
- High or high-normal TSH (2.5-10.0)
- Normal Free T4
- Normal or low-normal Free T3
What this means: Your thyroid is starting to struggle, but it’s still producing enough hormone to keep levels in the ‘normal’ range. Many people in this category have symptoms and benefit from treatment.
Pattern 3: Conversion Problem
- Normal TSH
- Normal or high Free T4
- Low Free T3
- Often elevated Reverse T3
What this means: Your thyroid is producing hormone, but your body isn’t converting T4 to active T3 efficiently. This requires addressing underlying causes like stress, inflammation, or nutrient deficiencies.
Pattern 4: Hashimoto’s (Early Stage)
- Normal TSH
- Normal Free T4 and T3
- Elevated TPO and/or TG antibodies
What this means: You have autoimmune thyroid disease, but your thyroid function hasn’t deteriorated yet. This is the ideal time for intervention to slow disease progression.
Pattern 5: Hyperthyroidism
- Low or suppressed TSH
- High Free T4
- High Free T3
What this means: Your thyroid is producing too much hormone. This requires medical attention and can be caused by Graves’ disease, toxic nodules, or thyroiditis.
What Your Doctor Doesn't Always Tell You About Thyroid Testing
1. Timing of Your Blood Test Matters
TSH levels follow a circadian rhythm, peaking in the early morning (2-4 AM) and reaching their lowest point in the afternoon. For consistent results:- Have your blood drawn in the morning (ideally before 9 AM)
- Test at the same time of day for follow-up tests
- Fast for at least 8 hours (though water is fine)
2. If You’re Taking Thyroid Medication
Take your medication AFTER your blood test, not before. Taking it beforehand can artificially elevate your thyroid hormone levels and give misleading results. Read more: How to Make Your Thyroid Medication Work Better3. One Test Isn’t Enough
Thyroid function can fluctuate, especially in early Hashimoto’s. If you have symptoms but normal results, repeat testing in 3-6 months.4. ‘Normal’ Doesn’t Mean ‘Optimal’
Laboratory reference ranges are based on 95% of the tested population. This includes people with undiagnosed thyroid problems. Being ‘within range’ doesn’t guarantee you’re at your optimal level. Many people feel best when their results are in specific parts of the range:- TSH: 1.0-2.0 mIU/L
- Free T4: Upper half of range
Getting Comprehensive Thyroid Testing in Australia
Option 1: Request Specific Tests from Your GP
Be proactive and specifically ask for:- TSH
- Free T4
- Free T3
- TPO antibodies
- TG antibodies
Option 2: Functional Medicine Testing
Functional medicine practitioners routinely order comprehensive thyroid panels, including all the markers above, plus Reverse T3 and supporting tests like:- Vitamin D
- Iron studies (ferritin)
- Vitamin B12
- Zinc and selenium
- Cortisol patterns
Summary: Your Thyroid Testing Checklist
A comprehensive thyroid blood test should include:
Essential markers:
- ✓ TSH (optimal: 1.0-2.0)
- ✓ Free T4 (optimal: upper half of range)
- ✓ Free T3 (optimal: upper third of range)
- ✓ TPO antibodies (optimal: < 9)
- ✓ TG antibodies (optimal: < 40)
Advanced markers (if symptoms persist):
- ✓ Reverse T3
- ✓ Supporting nutrients (vitamin D, iron, B12, zinc, selenium)
Remember: Understanding what each marker measures and how they relate to each other is just as important as the numbers themselves. Thyroid health is about patterns, not just individual values.
Get Expert Interpretation of Your Thyroid Results
At Lucy Rose Clinic, we specialise in comprehensive thyroid function testing and expert interpretation. We don’t just tell you if you’re ‘in range’, we analyse your complete thyroid picture and create personalised treatment plans to optimise your thyroid health. Whether you’re struggling with unexplained symptoms, have been told your results are ‘normal’ despite feeling unwell, or want to understand your existing thyroid condition better, we’re here to help. Book your comprehensive thyroid assessment today and take control of your thyroid health.