Thyroid: why TSH alone misses 5 of 7 patterns

Why your TSH value tells half the story

The standard GP thyroid check usually consists of one value: TSH. Sometimes fT4 is added. That is it. The active hormone fT3 is almost never tested on suspicion in German practices, and Anti-TPO antibodies even less so.

The problem: TSH is a control signal from the pituitary. It does not tell you how much active hormone reaches your cells. A woman with TSH 2.5, fT4 in range and low fT3 is “healthy” on a standard report. Functionally, she often is not. That is the same gap we describe in Your values are all normal.

A UK cohort study of 2,779 adults over 20 years showed: women with a TSH above 2 mU/l had an eightfold higher risk of developing hypothyroidism. When Anti-TPO antibodies were also positive, the risk rose 38-fold (Vanderpump et al., 1995 [1]). 2 mU/l sits in the middle of the “reference range”. On a standard report, that does not show up as a warning.

aescolab’s thyroid panel does not only look at TSH, but at fT3, fT4, Anti-TPO and selenium. From those four markers it differentiates seven dysfunction patterns, three of them with a recommendation for prompt medical assessment. A standard blood count does not do that.

The 7 thyroid patterns compared

Thyroid patterns are not a theoretical exercise. They follow from how the four markers interact, and they lead to different next steps. Here is how aescolab breaks them down in the report.

The standard GP check with TSH alone reliably detects only patterns A (overt) and F (isolated TSH elevation). B, C, D, E and G need at least fT3, fT4 and Anti-TPO.

Pattern E is the most common pattern in women with unexplained exhaustion. fT3 is low; fT4 and TSH sit in the reference range. The GP says: everything is fine. Functionally, the thyroid is running in emergency mode. Unexplained fatigue in women also often involves ferritin below the functional optimum — another marker the standard check frequently skips.

fT3: the active hormone almost nobody measures

fT3 is the biologically active thyroid hormone. More than 80 percent of it is not made in the thyroid itself, but converted from fT4 in the liver and kidney. The enzymes that do this are called deiodinases. And they need selenium.

About 15 to 20 percent of the population carry a genetic polymorphism in the DIO2 gene that structurally impairs conversion of T4 to T3. An Italian study of 140 patients after thyroid surgery showed: carriers of the Thr92Ala variant had significantly lower fT3 values despite adequate levothyroxine substitution (Castagna et al., 2017 [2]).

In one in five women, conversion is therefore genetically constrained. Even with optimal TSH and fT4, fT3 can still be clearly too low. aescolab’s optimal range for fT3 is 3.0 to 3.5 pg/ml. The standard reference range only starts at 1.58 pg/ml. Between those two values lie worlds in your mitochondria’s energy production.

That is exactly why the standard check is not enough. Testing fT3 costs a few euros more and answers the decisive question: does the active hormone reach your cells?

Anti-TPO: an early sign before TSH rises

Hashimoto’s is the most common cause of hypothyroidism in Central Europe and is now considered the most common autoimmune disease overall (Caturegli et al., 2014 [3]). Women are affected far more often than men; depending on the study, the ratio sits between 4:1 and 8:1.

Less well known: Anti-TPO antibodies can be elevated years before the first TSH change. That is the phase in which the immune system is already attacking the thyroid, but reserve capacity still compensates for the damage. You feel exhausted, sometimes restless, you sleep badly. TSH is 2.4 and the GP sends you home.

If your Anti-TPO sits at 22 IU/ml, the standard check says: normal (cut-off <35). aescolab uses an optimal range below 5 IU/ml. Anything above that is treated as a hint of beginning or existing autoimmune activity. Your endocrinologist gets this information years earlier than with TSH follow-up alone.

In the aescolab report this is flagged as a TPO-standalone pattern: elevated antibodies with otherwise normal function. The recommendation is not panic, but a TSH/fT4 check every six to twelve months plus concrete measures aimed at lowering antibodies.

Selenium: the underestimated lever

Selenium is the biochemical hub of thyroid function. It is a cofactor of the deiodinases that convert T4 into T3, and a component of glutathione peroxidase, which protects thyroid tissue from oxidative stress.

A systematic review and meta-analysis in the journal Thyroid evaluated 35 randomised controlled trials. In the Anti-TPO subset (29 cohorts, 2,358 participants), selenium lowered antibodies significantly (SMD −0.96). In patients not on hormone therapy, TSH also fell (Huwiler et al., 2024 [4]). A second meta-analysis of 17 RCTs and 1,911 participants confirms the effect on Anti-TPO (Zuo et al., 2021 [5]).

Low vitamin D levels are additionally associated with higher Anti-TPO values. An observational study of 101 patients showed a negative correlation between vitamin D and Anti-TPO (r = −0.49) in the Anti-TPO-positive subgroup (Dabeer et al., 2020 [6]). Another investigation documented clearly lower vitamin D levels in women with Hashimoto’s (21.9 vs. 42.3 nmol/l in healthy controls) (Siddiq et al., 2023 [7]).

Concretely: with a documented selenium deficiency and elevated Anti-TPO, targeted selenium substitution (typically 100 to 200 µg per day, medically supervised) is an evidence-based lever. Anyone who takes 200 µg blindly, without knowing their own status, risks oversupply. Selenium without a status value can harm people whose levels are already normal. Measure first, then substitute in a targeted way — the same rule as in Supplements on suspicion.

Soils in Germany are selenium-poor, so dietary supply is often structurally suboptimal. aescolab tests selenium in the Empower and Women’s Health panels. The optimal range is 140 to 160 µg/l; the standard reference range already starts at 90.

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When medical assessment is urgent

Three of the seven patterns should be assessed by a doctor within weeks, not at the next routine check. Pattern A (overt hypothyroidism), pattern D (hyperthyroidism) and pattern G (sick euthyroid).

Pattern G is particularly important to know. Here fT3 is low, but TSH is normal or low. It classically appears in energy deficits: severe calorie restriction, intense training without enough recovery, chronic stress. The body actively throttles metabolism. That can make sense as a short-term adaptation, but becomes a problem when it is chronic.

Studies on subclinical hypothyroidism show that hormone substitution in pure pattern-B findings (TSH slightly elevated, fT4 normal) does not improve symptoms in every case. A JAMA meta-analysis of 21 RCTs with 2,192 adults found no benefit of levothyroxine on quality of life or thyroid-specific symptoms (Feller et al., 2018 [8]). That is an important point: not every slightly elevated TSH needs immediate therapy. It does need differentiated diagnostics that assign the pattern.

International consensus statements from the ATA, BTA and ETA recommend that future studies of levothyroxine–liothyronine combination therapy should also consider deiodinase polymorphisms (Jonklaas et al., 2021 [9]). That is a signal that impaired conversion is now taken seriously as a clinically relevant mechanism.

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