5 Lab Markers Your Doctor Isn't Checking — But Should Be

Ferritin — Your Hidden Iron Problem

This one drives me up a wall. Ferritin is your body's iron storage protein. It tells you how much iron is banked in reserve — not just circulating in your blood at this moment, but stored and available for the processes that need it. Hair follicle cells are among the fastest-dividing cells in the human body. They are voraciously hungry for iron. And they are also among the first cells your body will deprioritize when iron stores run low, because growing hair is a luxury your biology can sacrifice when resources get scarce.

The standard lab range starts at 12. Twelve. That means if your ferritin comes back at 15, your doctor will look at the result, see it falls within the reference range, and tell you it's normal. Meanwhile, your hair follicles are starving. Research consistently shows that ferritin needs to be above 70 — ideally closer to 80 or higher — to adequately support hair growth. A woman with a ferritin of 20 is not fine. She's depleted. And the gap between 20 and 70 represents months of hair that could have been growing but wasn't.

This is the single most commonly missed marker in hair loss workups. I've seen it hundreds of times. Patient after patient told their labs were normal while sitting at a ferritin of 18, 22, 30. It's maddening.

Free T3 — The Thyroid Marker That Actually Matters

Most doctors screen thyroid function with a single test: TSH. Thyroid Stimulating Hormone. It's a pituitary hormone that tells your thyroid gland to produce more thyroid hormone. When the thyroid is underperforming, TSH goes up. So a high TSH flags hypothyroidism. Simple enough.

Except it misses a huge piece of the puzzle. TSH tells you what the pituitary is requesting. It doesn't tell you what the body is actually using. Free T3 does. Triiodothyronine — free T3 — is the active form of thyroid hormone. The one that actually enters your cells, drives your metabolism, and directly impacts the hair growth cycle.

You can have a perfectly normal TSH and a low Free T3. This happens more often than people realize, especially in cases of poor T4-to-T3 conversion, which can be caused by stress, nutrient deficiencies (selenium, zinc), gut dysfunction, or chronic inflammation. The thyroid gland might be producing adequate T4. The pituitary might be satisfied. But the cells — including your hair follicle cells — aren't getting enough active hormone. Your TSH looks fine on paper. Your hair is still falling out. And nobody thinks to check why.

DHT — The Hormone Everyone Blames (Without Measuring)

Dihydrotestosterone. The villain of every hair loss article you've ever read. And yes, DHT plays a role in androgenetic alopecia — it binds to receptors in susceptible hair follicles and triggers miniaturization, the gradual shrinking of the follicle that produces thinner, shorter, weaker hairs until eventually it produces nothing at all.

But here's what gets overlooked constantly: most doctors who prescribe finasteride or recommend DHT-blocking shampoos never actually measure DHT levels. They just assume. Patient has thinning? Must be DHT. Here's a blocker. Good luck.

The reality is more complicated. Not everyone with hair loss has elevated DHT. And not everyone with elevated DHT loses their hair. Follicle sensitivity to DHT varies enormously based on genetics. What matters is the relationship between your circulating DHT levels, your follicle sensitivity, and the other factors in your hormonal ecosystem. Measuring DHT — along with total and free testosterone and DHEA-S — gives you actual data to work with instead of assumptions. Maybe you need a DHT intervention. Maybe you don't. The labs will tell you.

Vitamin D — The Sunshine Hormone Your Follicles Crave

Vitamin D isn't really a vitamin. It's a hormone. A steroid hormone that influences over 200 genes in the human body, including genes directly involved in the hair follicle growth cycle. Specifically, vitamin D receptors play a critical role in the anagen phase — the active growth phase of hair. When vitamin D is low, the growth cycle shortens. Follicles enter the resting phase prematurely. More hairs fall. Fewer grow.

Most labs flag vitamin D as "low" only when it drops below 30 ng/mL. But research on hair health — and frankly, on overall health — points to an optimal range of 50 to 80. That means someone sitting at 32 gets told they're fine. They're not. They're suboptimal by a wide margin. And in South Florida, where you'd think everyone walks around with sky-high vitamin D from the sunshine, we still see patients routinely coming in at 25, 30, 35. Sunscreen, indoor lifestyles, darker skin tones that require more UV exposure to synthesize the same amount — it all adds up to widespread insufficiency.

CRP — The Inflammation Signal Nobody Connects to Hair Loss

C-Reactive Protein. A marker of systemic inflammation that most people have never heard of in the context of hair loss. CRP is typically ordered to assess cardiovascular risk. But inflammation doesn't compartmentalize. It doesn't attack your arteries and politely leave your hair follicles alone. When CRP is elevated, it signals that your body is running a chronic inflammatory response — and that response disrupts everything, including follicular function.

Elevated CRP can indicate gut permeability, food sensitivities, chronic infections, autoimmune activation, metabolic dysfunction, or simply the cumulative inflammatory burden of a modern diet and high-stress lifestyle. Any of these can contribute to hair loss, and many of them go completely undetected without this one simple blood test.

The standard cutoff is under 3.0 mg/L. Functional practitioners — and anyone serious about longevity — want to see it under 1.0. There's a world of difference between a CRP of 0.5 and a CRP of 2.8, even though both technically fall within "normal" range.