The most expensive mistake in treating hair loss is not the wrong product. It is the wrong diagnosis.
Androgenetic alopecia — the DHT-driven hair loss that most people assume they have — accounts for around 95% of male hair loss cases. But that leaves a meaningful percentage of people who are experiencing shedding from ferritin deficiency, thyroid dysfunction, vitamin D insufficiency, or insulin resistance. These causes are not only different in mechanism — they require entirely different interventions. And they are fully reversible.
Starting finasteride when your ferritin is 18 ng/mL is not wrong, exactly. But it is incomplete. The deficiency will continue driving shedding while you wait for a DHT-blocking drug to work. Getting the blood tests first is not a delay — it is the fastest path to the right answer.
Knowing what you are treating changes everything about how you treat it.
The Essential Panel
1. Ferritin (Iron Storage) — Critical
Ferritin is the stored form of iron in the body. It is the single most commonly missed cause of diffuse hair shedding.
The problem with standard laboratory ranges: most labs flag ferritin as “normal” above 12–15 ng/mL. For hair growth, the functional target is 70 ng/mL or above. A ferritin of 22 ng/mL will come back labelled normal on a standard report while actively suppressing follicular function.
Hair follicles require iron for rapid cell division in the hair matrix. Below optimal ferritin, the body prioritises iron for red blood cell production over hair follicles, which are metabolically active but not survival-critical.
Target for hair health: ≥70 ng/mL
2. Vitamin D (25-OH) — Critical
Vitamin D receptors (VDR) are expressed in hair follicles. Deficiency is strongly associated with alopecia areata and contributes to diffuse hair thinning across hair loss types. It is one of the most prevalent deficiencies globally — particularly in people who spend most of their time indoors.
Most standard labs consider 20 ng/mL sufficient. For hair health (and general wellbeing), the functional target is 40–80 ng/mL.
Target for hair health: 40–80 ng/mL
3. TSH (Thyroid-Stimulating Hormone) — Critical
Both hypothyroidism and hyperthyroidism cause diffuse hair loss — and thyroid dysfunction frequently presents without the classic symptoms people expect. A simple TSH panel (add T3 and T4 for a complete picture) can rule this out or reveal a fully treatable cause.
Untreated thyroid dysfunction driving hair loss will not respond to finasteride or minoxidil. Treating the thyroid, however, often produces significant hair recovery without any specific hair loss intervention.
Optimal TSH range: 0.4–2.5 mIU/L (note: within-range does not mean optimal for everyone)
4. Complete Blood Count (CBC) — High Priority
A CBC detects anaemia — a reduced capacity to carry oxygen in the blood, which compromises the oxygen supply to hair follicles. Haemoglobin, haematocrit, and red blood cell values together reveal whether oxygenation is a limiting factor in your hair growth.
Chronic anaemia is a common, correctable driver of telogen effluvium.
Reference: Haemoglobin ≥13.5 g/dL (men), ≥12 g/dL (women)
5. Zinc (Serum) — High Priority
Zinc is essential for 5-alpha-reductase regulation, protein synthesis, and rapid cell division in the hair matrix. Low serum zinc has been found in a significant proportion of androgenetic alopecia patients and is strongly associated with alopecia areata.
Note: serum zinc can appear normal while intracellular zinc is depleted. If your diet is low in meat and shellfish, treating empirically with 15–30mg/day zinc is a reasonable approach even without a definitive deficiency on paper.
Target: 80–120 mcg/dL
6. DHT (Dihydrotestosterone) — High Priority
DHT is the primary androgen driving follicular miniaturisation in androgenetic alopecia. A baseline measurement is useful for two reasons: it confirms that DHT-mediated hair loss is what you are dealing with, and it gives a reference point for measuring the response to finasteride (which reduces serum DHT by 60–70%).
Important caveat: Serum DHT does not perfectly correlate with scalp DHT. A normal serum DHT does not rule out AGA in a genetically predisposed individual.
Reference (men): 30–85 ng/dL
7. Cortisol (Fasting, Morning) — High Priority
Chronically elevated cortisol is both a cause and an amplifier of hair loss. High cortisol drives telogen effluvium by shifting follicles into the resting phase. In people with androgenetic alopecia, stress accelerates the progression of miniaturisation.
Morning serum cortisol (drawn at 8–9am) provides a reliable snapshot of baseline cortisol status.
Reference: 6–23 mcg/dL morning (context-dependent)
8. Fasting Blood Glucose + HbA1c — Medium Priority
Insulin resistance and chronically elevated blood sugar damage the microvascular supply to hair follicles. There is a well-documented association between central scalp hair loss and metabolic syndrome. This is particularly relevant for anyone with family history of diabetes, obesity, or PCOS.
Reference: Fasting glucose <100 mg/dL; HbA1c <5.7%
9. Vitamin B12 — Medium Priority
B12 deficiency causes diffuse shedding and is extremely common in people following vegetarian or vegan diets. Like ferritin, standard “normal” ranges are often too low to represent optimal hair health.
A result of 200 pg/mL may be labelled normal. For hair health, target 400 pg/mL or above.
Target for hair health: ≥400 pg/mL
10. CRP + ESR (Inflammatory Markers) — Medium Priority
C-reactive protein and erythrocyte sedimentation rate indicate systemic inflammation. Chronic inflammatory conditions disrupt the hair growth cycle and are a known driver of alopecia areata and other inflammatory alopecias.
If your hair loss is patchy, comes with scalp tenderness, or does not match a typical AGA pattern, inflammatory markers are important to include.
Target: CRP <1 mg/L (optimal)
11. ANA Panel (Antinuclear Antibodies) — Medium Priority
The ANA panel rules out lupus and other autoimmune conditions that cause scarring alopecia. If hair loss is patchy, comes with scalp discomfort, or progresses in an atypical pattern, a positive ANA warrants further rheumatological investigation.
For standard patterned AGA, this is a lower priority. For any presentation with unusual features, it is essential.
12. Total and Free Testosterone — Medium Priority
Total and free testosterone help contextualise DHT levels — very high testosterone provides more substrate for DHT conversion. This panel is particularly important for women experiencing hair loss (ruling out PCOS) and for men on testosterone replacement therapy.
Reference (men): Total testosterone 400–900 ng/dL
Reading Your Results
A few principles for interpreting these results in the context of hair health:
“Normal” is not the same as “optimal.” For ferritin, vitamin D, and B12 in particular, the standard laboratory reference ranges were established to prevent deficiency disease — not to support the metabolically demanding process of hair growth. Always look at where your values fall relative to the targets listed above.
Multiple deficiencies can coexist. Finding a low ferritin does not mean the thyroid is fine. It is worth checking the full panel rather than stopping at the first result.
Recheck at 3 months. Once you begin correcting deficiencies, retest to confirm the values are moving in the right direction. Ferritin in particular can take 3–6 months of supplementation to normalise.
Frequently Asked Questions
Do I need all 12 tests? The critical tier (ferritin, vitamin D, TSH) is the minimum. The full panel is ideal if you are beginning a serious treatment protocol, as it gives you the most complete picture and rules out causes that would otherwise waste months of the wrong treatment.
My doctor said my results are normal. Should I still be concerned? If your ferritin is between 15–70 ng/mL, your vitamin D is between 20–40 ng/mL, or your B12 is between 200–400 pg/mL, your results are technically “normal” by standard ranges while still being suboptimal for hair health. Use the targets in this article, not just the lab reference ranges.
Can I order these tests without a doctor? In many countries, direct-to-consumer lab testing is available. In others, a GP referral is required. Either way, having a doctor review the results and advise on supplementation is recommended, particularly for iron and vitamin D where both deficiency and excess have real consequences.
How often should I retest? At baseline before beginning treatment, then every 6 months if you are actively managing deficiencies. Once your values are stable and optimal, an annual check is sufficient.