Short answer: start with TSH and free T4, but don’t expect the thyroid alone to explain 10kg — an underactive thyroid typically accounts for only a few kilograms, so a gain this size usually needs a broader panel to find the real cause.
Thyroid testing is the right starting point — just not the whole answer
A TSH blood test is the standard first step toward diagnosing hypothyroidism, with free T4 as the usual follow-up to confirm a diagnosis if TSH comes back abnormal. Screening for thyroid disorders is considered part of the routine initial evaluation of unexplained weight gain — so if your doctor orders this first, that’s appropriate, not a brush-off.
But here’s the honest limit of what it explains: an underactive thyroid typically accounts for only a few kilograms of weight gain, and part of that is fluid retention rather than fat. A 10kg gain over six months, with no change in diet, is larger than hypothyroidism alone usually produces — even if your thyroid numbers do turn out to be abnormal, something else is likely contributing too.
What else should actually be checked
- Fasting glucose and HbA1c — screens for insulin resistance or pre-diabetes, a common and often overlooked contributor to unexplained weight gain
- Complete blood count with ferritin (iron studies) — low iron causes fatigue and metabolic changes that can look similar to thyroid issues on the surface
- Vitamin D — commonly low, commonly contributes to fatigue and weight changes, rarely tested unless specifically requested
- Cortisol or other hormone tests, depending on your specific symptoms and history — relevant if other signs point toward adrenal or broader hormonal causes
A single TSH test doesn’t cover any of these. If that’s the only test ordered so far, it’s reasonable to ask directly what else should be ruled out given the size of the change.
What to say if you’re only offered a thyroid test
“Given this is a 10kg change over six months, not explained by diet, can we also check fasting glucose, HbA1c, ferritin and vitamin D — not just thyroid?” This is a specific, answerable request, not an unreasonable one for a change this size.
Why this matters
A 10kg gain over six months without an explanation is significant enough to warrant a real evaluation, not a single test and a shrug. It doesn’t mean something is seriously wrong — but it does mean the cause is worth actually finding, since treating the wrong thing (or nothing) leaves the real driver unaddressed.
Getting Started
Ask for the fuller panel above before accepting “your thyroid is fine” as the end of the conversation — a normal TSH only rules out one possible cause, not all of them. See verified endocrinology clinics in Turkey, or ask our AI assistant if you want help thinking through which tests are most relevant to your specific symptoms.
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