Thyroid, Iron, Vitamin D: The Blood Work to Run Before Blaming Genetics
A big share of men who think they're going bald are shedding from something reversible. Three cheap lab values tell you which — and it's the step almost everyone skips.
Before you spend a dollar on finasteride, spend it on a blood draw. A meaningful share of men who assume they're going bald from genetics are actually shedding from something reversible — and three cheap lab values will tell you which camp you're in. This is the step almost everyone skips, and it's the highest-value hour in the whole process.
01Why "it's just genetics" is often wrong
Androgenetic alopecia has a signature: gradual, patterned recession at the hairline and crown. But diffuse thinning all over — the kind where your part looks wider and your whole scalp feels thinner — frequently has a different cause. And unlike genetic loss, those causes are often fixable. Blaming genetics for a thyroid problem means treating the wrong thing for years.
Three under-diagnosed drivers of hair thinning: thyroid dysfunction (TSH), iron deficiency (ferritin), and low vitamin D (25-OH vitamin D). All three are common, all three are reversible, all three are cheap to check.
02What each test tells you
| Test | What it checks | Why it matters for hair |
|---|---|---|
| TSH (thyroid) | Thyroid function | Both under- and over-active thyroid can cause diffuse shedding |
| Ferritin (iron stores) | Your true iron reserves | Low ferritin is a well-known trigger for hair shedding, especially telogen effluvium |
| 25-OH vitamin D | Vitamin D status | Deficiency is linked to hair-cycle disruption and is extremely common |
A note on ferritin specifically: a standard iron panel can look "normal" while your ferritin — the storage form — is low. Ask for ferritin by name. Many hair-relevant iron issues hide behind a normal-looking basic panel.
03How to actually get these done
You have more options than "beg your GP":
- Telehealth lab ordering: many platforms will order these three and send you to a Quest or Labcorp for the draw.
- Direct-to-consumer labs: you can often order the panel yourself online, no doctor visit required, and get results in a portal.
- Your primary care doctor: free or cheap with insurance if you frame it as "diffuse hair shedding, want to rule out reversible causes."
04What to do with the results
If a value comes back off, you've potentially found a fixable cause — correct the deficiency or treat the thyroid, and the shedding often improves over the following months. If all three come back clean and you have the classic patterned recession, that points toward genetic loss, and now the DHT-blocker conversation makes sense. Either way, you've stopped guessing.
Supplementing blindly is its own trap — mega-dosing vitamin DPaid link or ironPaid link without knowing your levels can be pointless or even harmful (iron especially). Test first, then correct what's actually low.
Order labs and get a treatment plan
Sesame Care
Telehealth visit + lab orderingSame-day telehealth visits for FDA-approved hair-loss prescriptions, from $44.
Sesame connects you with providers for FDA-approved, brand-name medications — no compounded products.
See Sesame Care options Paid linkCare Bare Rx
Hair-loss consult with a providerTelehealth hair-loss intake with prescription minoxidil and finasteride options.
See Care Bare Rx options Paid linkRxSpan MD
Provider match for evaluationTelehealth program connecting you with a licensed provider for hair-loss treatment.
See RxSpan MD options Paid linkThe men who win at hair loss are the ones who diagnose before they treat. Three lab values. One draw. Do it before you commit to years of medication for a problem you might not have.
Affiliate disclosure. Male Hair Advice may earn a commission when you use the links marked “Paid link,” at no additional cost to you. We only include providers we believe are relevant to the topic, and commercial relationships never change our editorial assessments.