Hair shedding or thinning? Here are the blood tests to ask for, from ferritin and thyroid to hormones and blood sugar, and what “normal” results may miss.
You’ve tried the serums. The shampoos. The gummies. The scalp massager.
Has anyone checked your labs?
Hair loss is often a sign that something else is going on inside your body, and a few simple blood tests can help find it. But “normal” results don’t always tell the whole story, and a basic panel often misses the pieces that matter most.
This post covers which tests to ask for, what each one can tell you, what “normal” may miss, and what I look at from a functional medicine and pharmacist perspective. It focuses mainly on women, though some of it applies to men too. It’s educational and isn’t a substitute for care from your own healthcare team or dermatologist. Numbers in brackets point to the references at the end.
For the full list of root causes, see why your hair may be shedding. This one is about what to ask for.
Not everyone with hair loss needs a big panel. A good starting point is a conversation about your story and a scalp exam. Your provider or dermatologist will ask about:
Sudden or gradual? Sudden, all-over shedding often follows a trigger two to three months earlier, such as illness, surgery, childbirth, a crash diet, or a stressful period.[1]
Shedding all over, thinning at the part, or patchy loss.
Your cycle, pregnancy history, diet, medications, and family history.
Blood tests are most helpful when shedding is ongoing, when it’s been months, or when you have other symptoms such as fatigue, cycle changes, or sleep trouble.
Chosen based on your story, not a one-size-fits-all panel.
The test I’d ask about first.
Ferritin shows your stored iron. Low iron stores are common in women, especially with heavy periods, pregnancy, plant-based eating, or digestive problems, and iron deficiency is considered worth checking and correcting in hair loss.[2]
The catch is what “normal” means. Lab ranges are built to detect deficiency, not to show where your hair does best. The World Health Organization defines iron deficiency in adults as a ferritin of:[3]
ng/mL ferritin
ng/mL ferritin
Some experts argue that higher levels may be better for hair, but there’s no single agreed target, and the research is mixed.[4]
Ask for your actual number, not just “normal.” Ferritin rises with inflammation, so it can look normal even when iron is low, which is why I add transferrin saturation and sometimes CRP.[3] And please don’t start iron on your own. Too much is harmful, and it won’t help if you’re not low. (More on the hidden causes of anemia.)
Many standard panels check TSH alone.
Both an underactive and an overactive thyroid can cause hair thinning, along with fatigue, mood changes, and weight changes.[5], [6]
Antibodies can point to autoimmune thyroid disease like Hashimoto’s. Reverse T3 is sometimes ordered, but its value is debated, so I interpret it cautiously. Already on thyroid medication and still shedding? See why thyroid medication works better for some people than others.
Worth checking if you’re at risk.
Low vitamin D is linked to hair loss in some studies, but whether supplementing helps people who aren’t deficient isn’t proven.[2] I’d check it if you’re at higher risk, such as limited sun, darker skin, living farther north, or autoimmune disease, because guidelines don’t advise routine testing for everyone.[7] If you’re low, work with your provider on a dose and recheck. (See my complete guide to vitamin D.)
Often part of a hair loss workup.
B12 deficiency can cause fatigue, brain fog, and low mood.[8] It’s more common with acid-reducing medicines, metformin, vegetarian or vegan diets, and digestive conditions.
I don’t test everyone.
Low zinc can be linked to hair shedding, but the evidence is mixed and blood levels are hard to interpret.[2] I consider it with digestive problems, restrictive diets, or other signs of deficiency.
Too much zinc can cause problems, including copper deficiency.
A normal glucose doesn’t rule it out.
Insulin resistance affects hormones, especially androgens, and it’s common in PCOS, which is a frequent cause of hair thinning.[9]
Insulin can start rising years before glucose does. (See why fasting insulin matters more than fasting glucose.)
When thinning comes with irregular cycles, acne, unwanted hair growth, or a sudden change.
SHBG lets your provider calculate free testosterone, and prolactin and thyroid problems can mimic or worsen PCOS symptoms. These help sort out PCOS and androgen-related hair loss.[9] I cover that in my post on PCOS.
Estrogen, progesterone, and FSH swing widely during the transition, so a single test can look normal one day and very different the next. That’s why perimenopause is usually recognized by your symptoms and age, not one blood test.[10] Use my early signs of perimenopause checklist.
Depending on your story.
| If You Have… | Ask About… |
|---|---|
| Fatigue, heavy periods, restless legs | Ferritin, CBC, transferrin saturation |
| Fatigue, cold or heat sensitivity, weight changes | TSH, free T3 and T4, TPO antibodies |
| Limited sun, darker skin, autoimmune disease | Vitamin D |
| Tingling, fatigue, low mood, or acid-reducing meds | B12 |
| Cravings, afternoon crashes, stubborn weight | Fasting glucose, insulin, A1c |
| Irregular cycles, acne, unwanted hair growth | Testosterone with SHBG, DHEA-S, prolactin |
| Digestive symptoms or unexplained low iron | Celiac screen |
| Patchy loss, itchy or painful scalp | A dermatologist visit |
If your hair changes come with other symptoms, a good first step is understanding your hormone pattern. My free Hormone Type Assessment is a short quiz that helps you see whether your symptoms point toward one of these, so you know what to ask about next:
This test claims to measure minerals in a sample of your hair to diagnose deficiencies. But when researchers sent identical hair samples to commercial labs, the results were unreliable and inconsistent, and the interpretations weren’t medically sound.[13] It’s often sold alongside supplements, so I’d skip it.
When someone asks me about hair loss, I look at the whole picture:
What happened in the three to six months before the shedding started.
The tests above, chosen based on your story, not a one-size-fits-all panel.
Protein, iron-rich foods, and overall intake. (Here are protein sources that support hormonal stability.)
Many common medicines can cause hair loss, and as a pharmacist, I always check. Please don’t stop any medication on your own.
Postpartum, perimenopause, PCOS, and menopause.
Absorption, rest, and load all matter. (See what a GI-MAP can show and being told it’s “just stress”.)
I also use my four working patterns to organize what I find:
Hair shedding, fatigue, low iron, low vitamin D or B12
Wired at night, tired by day, high stress, poor sleep
Blood sugar swings, cravings, acne, stubborn weight
Bloating, sluggish digestion, poor absorption
These are clues that organize questions. They don’t diagnose a cause.
Talk with your provider or a dermatologist if you have patchy hair loss, a burning, itchy, or painful scalp, scarring, loss of eyebrows or eyelashes, or sudden heavy shedding. Also see them if your hair loss comes with fatigue, a racing heart, cycle changes, or unexplained weight loss. And if hair loss is weighing on your mood, bring that up too.
And you don’t need to keep spending money on products that don’t address the cause. A few well-chosen tests, interpreted in the context of your story, can change the direction of your care.
If you haven’t yet, start with the free Hormone Type Assessment. And if you’d rather talk through what you’ve been experiencing, I offer a free discovery call. No pressure, just a conversation about whether functional medicine is the right next step for you.
Book Your Free Discovery Call →To your health and vitality, Dr. Ryan
Depending on your story, consider ferritin with a CBC and transferrin saturation, a thyroid panel (TSH, free T4, free T3, antibodies), vitamin D if you’re at risk, B12, fasting glucose, insulin, and A1c, and testosterone with SHBG, DHEA-S, and prolactin if you have signs of androgen excess.
The World Health Organization defines iron deficiency in healthy adults as a ferritin below 15 ng/mL, or below 70 ng/mL with inflammation. Some experts argue higher levels may be better for hair, but there’s no single agreed target.
Ferritin rises with inflammation, so it can look normal even when iron is low. Adding transferrin saturation, and sometimes CRP, gives a clearer picture.
Biotin can interfere with some blood tests, including thyroid tests. Ask your provider or lab how long to pause it before your draw.
No. A JAMA study of commercial labs found hair mineral analysis results were unreliable and inconsistent, with interpretations that weren’t medically sound.
For educational purposes only. Not a diagnosis, and not a substitute for care from your healthcare provider, dermatologist, or a licensed mental health professional. Do not start, stop, or change any medication or supplement without talking with your provider.
