Before you spend months and money on a hair-loss treatment, it's worth knowing whether something reversible is driving the shedding. A short, focused blood panel answers that — but only a handful of markers are actually worth checking, and which ones depend on your situation. This guide covers what to test, what each result rules in or out, and when a panel is worth it at all.
If you haven't yet, it helps to read the hormonal picture behind hair loss first — it explains why most pattern hair loss needs no testing, while diffuse shedding often does.
Quick Answer
The highest-value markers before treating hair loss are ferritin (iron stores), TSH and free T4 (thyroid), and vitamin D (25-OH). Testosterone with SHBG helps in specific cases, not routinely. A normal result is useful information, not a wasted test — it rules out reversible causes so you can treat the right thing.
The Markers Worth Checking
| Marker | What it checks | What it rules in or out | |---|---|---| | Ferritin | Iron stores (drops before anemia shows on a CBC) | Iron-related shedding — the highest-yield single test, especially in women (2007, 2022 meta-analysis) | | TSH + free T4 | Thyroid function | Hypo- or hyperthyroid-driven diffuse shedding, which is often reversible once treated (2024) | | Vitamin D (25-OH) | Vitamin D status | Deficiency associated with hair loss — worth correcting for your health, though not a proven regrowth cure (2024, 2021 review) | | CBC | Anemia, broad red flags | Anemia and other systemic issues behind heavy shedding | | Total testosterone + SHBG (+ free T) | Androgen status and how much is bioavailable | Useful only with other signs (in women, androgen excess; in men, low-T symptoms) — most pattern hair loss occurs at normal levels (review) | | DHEA-S / prolactin | Adrenal androgens / pituitary | Situational — women with signs of androgen excess or irregular cycles, not routine |
The first three rows — ferritin, thyroid, vitamin D — are the core panel for most people with diffuse shedding. The hormone rows matter in specific situations, not as a default.
Why Ferritin Is the One to Prioritize
Iron is the marker most likely to be both relevant and missed. Ferritin reflects your stored iron, and it can be low long before a standard blood count flags anemia — so a "normal CBC" doesn't mean your iron is fine. Low iron stores are more common in women with excessive hair loss, and the honest caveat from the hormonal overview applies here too: correcting a real deficiency is worthwhile, but iron is not a regrowth treatment for people who aren't deficient, and a normal ferritin doesn't rule out pattern hair loss.
At-Home vs. In-Lab
- At-home panels (finger-stick or mail-in) cover the core markers — ferritin, thyroid, vitamin D — and some services add a physician review of your results. Convenient, and enough for most people ruling out reversible causes.
- In-lab venous draw is the traditional route and is preferable when you want a full hormone panel or your clinician is ordering follow-up. If a home result is abnormal, expect to confirm it with a standard lab draw.
Either way, the point is the same: get the focused panel, not a scattershot one.
A Normal Result Is Not a Wasted Test
It's worth saying plainly, because it's the opposite of how tests are usually sold: if a cause was plausible — diffuse shedding, sudden onset, symptoms — then a normal panel is genuinely useful. It rules those causes out and points you back toward pattern hair loss with confidence, so you're not treating a thyroid or iron problem that isn't there. What isn't worth paying for is testing when nothing pointed to a cause in the first place (a man with a slow, classic receding pattern and no other symptoms).
Before you treat, test
Not sure what's driving your hair loss?
Hone's at-home panel covers the markers that matter most for hair loss — ferritin, thyroid, and vitamin D among them — with a licensed physician's review of your results. It's the diagnostics-first step before committing to a treatment.
Sources
- Rushton DH, Norris MJ, Van Neste D. Low iron stores: a risk factor for excessive hair loss in non-menopausal women. European Journal of Dermatology. 2007;17(6):507-511. PMID: 17951130.
- Iron Deficiency and Nonscarring Alopecia in Women: Systematic Review and Meta-Analysis. Skin Appendage Disorders. 2022;8(2):83-92. PMID: 35415182.
- Thyroid dysfunction as a cause of telogen effluvium: a retrospective study. Medicine (Baltimore). 2024;103(1):e36803. PMID: 38181279.
- Vitamin D deficiency in non-scarring and scarring alopecias: a systematic review and meta-analysis. Frontiers in Nutrition. 2024;11. PMID: 39416654.
- Gerkowicz A, et al. Role of vitamin D in hair loss: a short review. Journal of Cosmetic Dermatology. 2021;20(11):3345-3351. PMID: 34553483.
- Grymowicz M, Rudnicka E, Podfigurna A, et al. The Hormonal Background of Hair Loss in Non-Scarring Alopecias. Biomedicines. 2024;12(3):513. PMID: 38540126.