Symptom → lab tests
Which blood tests should you get for dry skin and brittle nails?
Short answer
Dry skin and brittle, ridged or spoon-shaped nails are common and usually environmental, but they are also classic signs of an underactive thyroid, iron deficiency, and low zinc, vitamin D or biotin — and, less often, diabetes or kidney and liver disease. A TSH, ferritin, CBC, zinc, vitamin D and a metabolic panel cover the treatable causes. A rash that is spreading, blistering or painful needs a clinician.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
When should you see a clinician instead of ordering a test?
- A rash that is spreading rapidly, blistering, or involves the mouth or eyes
- Dry skin with yellowing of the skin or eyes, or dark urine (liver)
- Skin changes with unexplained weight loss, fever or night sweats
- Nail changes in a single nail with dark streaks or lifting — see a dermatologist
Why these tests for dry skin and brittle nails?
Hypothyroidism slows skin turnover and oil production, producing dry, cool skin, coarse hair and brittle nails; TSH with free T4 is the highest-yield test. Iron deficiency causes brittle or spoon-shaped nails and hair shedding — ferritin catches it before anemia.
Zinc, vitamin D, biotin and essential fatty acids all contribute to skin barrier and nail strength. Zinc and vitamin D are the deficiencies most often found; biotin deficiency is rare but the test exists.
A metabolic panel and A1c screen for diabetes and kidney or liver disease, which cause dry, itchy skin through other mechanisms.
Which conditions do these tests help evaluate?
- Thyroid Problems — TSH, Free T4/T3 and antibodies to evaluate an under- or over-active thyroid.
- Anemia — CBC, iron studies, ferritin, B12 and folate to find the cause of fatigue and low energy.
- Hair Loss — Thyroid, iron/ferritin, hormones and vitamins behind unexplained shedding.
Which tests, and what do they cost?
Prices are cash-pay; every order adds one $6 lab processing fee. Physician authorization is included; no insurance or referral needed.
| Test or panel | Type | Price | Fasting | Results |
|---|---|---|---|---|
| Complete Thyroid PanelSaves $10.97 vs ordering the tests separately | Panel · 4 tests | $109.99 | No | 3–7 business days |
| Vitamin & Mineral Deficiency PanelSaves $106.92 vs ordering the tests separately | Panel · 9 tests | $189.99 | No | 3–5 business days |
| Women's Hair Health PanelSaves $401.82 vs ordering the tests separately | Panel · 19 tests | $469.99 | No | 4–7 business days |
| TSH (Thyroid Stimulating Hormone) | Test | $26.99 | No | 1–3 business days |
| Free T4 (Thyroxine) | Test | $23.99 | No | 1–3 business days |
| Ferritin | Test | $24.99 | No | 1–3 business days |
| CBC with Differential | Test · 14 biomarkers | $21.99 | No | 1–3 business days |
| Zinc | Test | $26.99 | Yes | 3–6 business days |
| Vitamin D, 25-Hydroxy | Test | $41.99 | No | 1–3 business days |
| Comprehensive Metabolic Panel | Test · 14 biomarkers | $22.99 | Yes | 1–3 business days |
| Hemoglobin A1c | Test | $21.99 | No | 2–4 business days |
| Biotin (Vitamin B7) | Test | $259.99 | No | 3–7 business days |
| Omega-3 Index | Test · 5 biomarkers | $69.99 | No | 7–10 business days |
Common questions
Can dry skin be a sign of a thyroid problem?
Yes — dry, cool, pale skin with brittle nails and hair is one of the classic presentations of hypothyroidism, usually with fatigue, weight gain or feeling cold. A TSH answers it.
What deficiency causes brittle nails?
Iron deficiency is the most common lab-confirmable cause, followed by zinc; biotin deficiency is rare in people eating a normal diet. Frequent wetting and drying of the hands is the most common non-deficiency cause.
Should I take biotin for my nails?
Only after testing — biotin supplements interfere with thyroid, troponin and hormone assays, and evidence for nail benefit is thin. If you already take it, stop 72 hours before any blood draw.
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.