Symptom → lab tests
What blood tests check for causes of unexplained weight gain?
Short answer
When weight climbs without a change in eating or activity, the testable causes are an underactive thyroid, insulin resistance and cortisol excess. The workup is TSH, hemoglobin A1c with fasting insulin and glucose, a lipid panel, and morning cortisol; PCOS markers are added for women with irregular cycles.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
When should you see a clinician instead of ordering a test?
- Rapid weight gain with swelling of the legs, shortness of breath or lying-flat breathlessness — seek care promptly
- Weight gain with a rounded face, purple stretch marks, easy bruising and high blood pressure — see a clinician
Why these tests for unexplained weight gain?
Thyroid hormone sets energy expenditure, so hypothyroidism is the first thing to exclude. Insulin resistance — high fasting insulin with normal or rising glucose — makes weight gain and hunger worse years before diabetes appears, and A1c shows where blood sugar has been over three months.
Cortisol excess is rare but produces central weight gain, and morning cortisol is the screen. For women, weight gain with irregular periods or acne points to a PCOS workup. Medications (steroids, some antidepressants and antipsychotics) are a common non-lab cause worth raising with a clinician.
Which conditions do these tests help evaluate?
- Unexplained Weight Gain — Thyroid, insulin, cortisol and metabolic markers behind stubborn weight changes.
- Thyroid Problems — TSH, Free T4/T3 and antibodies to evaluate an under- or over-active thyroid.
- Diabetes & Blood Sugar — A1c, fasting glucose and insulin to screen for prediabetes and diabetes.
- PCOS — Androgens, LH/FSH, insulin and thyroid markers to investigate PCOS.
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 |
|---|---|---|---|---|
| Metabolism & Weight Loss PanelSaves $105.93 vs ordering the tests separately | Panel · 8 tests | $119.99 | Yes | 2–5 business days |
| Complete Thyroid PanelSaves $10.97 vs ordering the tests separately | Panel · 4 tests | $109.99 | No | 3–7 business days |
| Pre-Diabetes PanelSaves $34.96 vs ordering the tests separately | Panel · 5 tests | $89.99 | Yes | 2–5 business days |
| TSH (Thyroid Stimulating Hormone) | Test | $26.99 | No | 1–3 business days |
| Hemoglobin A1c | Test | $21.99 | No | 2–4 business days |
| Insulin, Fasting | Test | $22.99 | Yes | 2–4 business days |
| Glucose, Fasting | Test | $24.99 | Yes | 1–3 business days |
| Lipid Panel | Test · 4 biomarkers | $24.99 | Yes | 1–3 business days |
| Cortisol (AM) | Test | $26.99 | No | 2–4 business days |
Common questions
Do I need to fast for these tests?
Yes for fasting insulin, fasting glucose and the lipid panel (8–12 hours, water is fine). TSH, A1c and cortisol don't require fasting; draw cortisol before 9 a.m.
My TSH is normal — could my thyroid still be the cause?
Unlikely. A normal TSH makes hypothyroidism improbable as the cause of weight gain; the metabolic tests (insulin, A1c) more often explain it.
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.