Is Thyroid Testing Worth It?

1. Pituitary gland releases TSH (thyroid-stimulating hormone)
2. TSH signals thyroid to produce T4 and T3
3. T4 converts to T3 in tissues (T3 is the active form)
4. High T4/T3 signals pituitary to reduce TSH (negative feedback)

The female predominance in thyroid disease is largely driven by autoimmune factors. Autoimmune thyroid disease (Hashimoto's thyroiditis, Graves' disease) accounts for 90% of thyroid conditions and is far more common in women. Hormonal fluctuations during pregnancy, postpartum, and menopause also play a role.^[6]

The subclinical population: 10-15% of people have positive thyroid antibodies (most commonly TPO antibodies) without symptoms—these individuals are at increased risk of developing thyroid dysfunction, often years later. Testing antibodies can identify this risk before TSH changes occur.

Function Health highlights that thyroid conditions "often remain underdiagnosed" because symptoms overlap with everyday issues like fatigue, stress, and ageing.^[4] The RACGP recommends against routine screening in asymptomatic people—but this guideline assumes symptoms are recognised and prompt testing.

The challenge: Many people attribute early hypothyroid symptoms to "just getting older" or "being stressed"—delaying diagnosis by years. For women over 35 with a 1 in 8 lifetime risk, establishing a baseline while healthy provides a reference point for future comparison.

The National Academy of Clinical Biochemistry found that more than 95% of normal individuals have TSH below 2.5 mIU/L.^[9] NICE (UK) recommends targeting 0.4-2.5 mIU/L for people on thyroid medication. The Australian Prescriber acknowledges that "the upper limit of normal may be too high for some populations."^[8]

The practical implication: A TSH of 3.5 mIU/L is technically "normal" but may be suboptimal—particularly if you have symptoms. Everyone has their own thyroid 'setpoint'—what's normal for one person may be high for another.

Lowering the upper limit from 4.0 to 2.5 mIU/L would quadruple the number of 'abnormal' results—turning millions of people into patients overnight. Without large trials showing benefit from treating TSH 2.5-4.0, most GPs follow the standard range.

The integrative approach: Many functional medicine practitioners use 2.5 mIU/L as their upper limit and consider treatment for symptomatic patients with TSH >2.5, particularly if antibodies are positive. This approach is controversial but has clinical rationale.

Research shows that people with subclinical hypothyroidism and positive TPO antibodies progress to overt hypothyroidism at a rate of 4-5% per year.^[8] Over 10 years, that's a 40-50% chance of developing clear-cut disease requiring treatment.

The integrative argument: Why wait for TSH to reach 10 when you could intervene at 5-7 with symptoms? Levothyroxine is safe, inexpensive, and may prevent years of suboptimal function. The conventional argument: Without large trials proving benefit, we risk overtreatment.

The middle ground: If you have symptoms, TSH >5, and positive antibodies, a 3-6 month trial of levothyroxine is reasonable—if symptoms improve, continue. If not, stop. This approach balances evidence with pragmatism.

TSH and fT4 are guideline-backed—your GP will know exactly what to do with these results:^[5]

• High TSH + Low T4: Likely hypothyroid—discussion of levothyroxine treatment, follow-up in 6-8 weeks
• Low TSH + High T4: Likely hyperthyroid—referral to endocrinologist often appropriate
• Normal TSH: Primary thyroid dysfunction unlikely (though not impossible)
• High TSH + Normal T4: Subclinical hypothyroidism—decision to treat depends on symptoms, antibodies, and degree of elevation
• Medicare rebate: TSH and fT4 covered when ordered by GP with clinical indication

If you want fT3, rT3, or treatment for TSH 2.5-5: Your GP may question the clinical utility or decline to order these tests. This isn't because they're wrong—it's because these approaches aren't part of RACGP guidelines. Consider seeing an integrative GP or endocrinologist if you want deeper investigation beyond standard guidelines.

The bottom line: Standard GPs follow evidence-based guidelines that focus on clear-cut disease. Integrative practitioners use a broader lens that may catch subtler imbalances—but with less research backing. Neither approach is inherently superior; they serve different patient preferences.

TSH alone: $30-40 (Medicare rebate available with GP referral)
Full panel (TSH, fT4, fT3, antibodies): $80-120

Compare this to the cost of years spent with suboptimal thyroid function—decreased productivity, increased healthcare visits, reduced quality of life. For women over 35 with a 1 in 8 lifetime risk, the $30-50 investment in baseline testing is trivial compared to the cost of not knowing.

Function Health's perspective: "Thyroid conditions often remain underdiagnosed" because symptoms are dismissed as normal ageing or stress. Testing provides clarity—either reassurance that your thyroid is functioning well, or early detection that allows intervention before dysfunction becomes severe.^[4]

TSH is the most sensitive screening test available—and it's enough for most people to start. With 1 in 8 women developing hypothyroidism and over 1 million Australians affected by undiagnosed thyroid conditions, testing is valuable for anyone with symptoms or risk factors.

The TSH 2.5 debate matters: While the standard reference range is 0.4-4.0 mIU/L, 95% of normal individuals have TSH below 2.5. If your TSH is 3.0-4.0 with symptoms, you're technically 'normal' but may benefit from closer monitoring or treatment—particularly if antibodies are positive. This is where integrative practitioners and conventional GPs differ most.

Subclinical hypothyroidism (TSH 5-10) with positive antibodies deserves serious consideration for treatment—the annual progression rate to overt disease is 4-5%, and levothyroxine is safe and inexpensive. A 3-6 month trial is reasonable if you have symptoms.

For women, particularly those over 35, postpartum, or with autoimmune history, thyroid testing isn't a luxury—it's a baseline worth establishing. The $30-50 cost is trivial compared to years spent attributing hypothyroid symptoms to 'just getting older.'

Bottom line: Test when you have symptoms or risk factors. Start with TSH. If you want deeper investigation (fT3, rT3, treatment for TSH 2.5-5), seek an integrative practitioner who can interpret these results effectively. The evidence is increasingly clear: earlier detection and intervention may prevent years of suboptimal function.