---
title: "What blood tests check for causes of unexplained weight gain?"
type: symptom
url: "https://www.test-well.com/symptoms/weight-gain"
symptom: Unexplained weight gain
aliases:
  - gaining weight without reason
  - can't lose weight
  - weight gain blood test
reviewed_at: 2026-09-06
review_status: reviewed
date_published: 2026-09-05
lab_fee_usd: 6
---

# What blood tests check for causes of unexplained weight gain?

> 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.


## 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](https://www.test-well.com/conditions/weight-gain) — Thyroid, insulin, cortisol and metabolic markers behind stubborn weight changes.
- [Thyroid Problems](https://www.test-well.com/conditions/thyroid-problems) — TSH, Free T4/T3 and antibodies to evaluate an under- or over-active thyroid.
- [Diabetes & Blood Sugar](https://www.test-well.com/conditions/diabetes-screening) — A1c, fasting glucose and insulin to screen for prediabetes and diabetes.
- [PCOS](https://www.test-well.com/conditions/pcos) — Androgens, LH/FSH, insulin and thyroid markers to investigate PCOS.

## Which tests, and what do they cost?

| Test or panel | Type | Price | All-in (one item + $6 fee) | Fasting | Results |
| --- | --- | --- | --- | --- | --- |
| [Metabolism & Weight Loss Panel](https://www.test-well.com/tests/metabolism-panel) | Panel (8 tests) | $119.99 | $125.99 | Yes | 2–5 business days |
| [Complete Thyroid Panel](https://www.test-well.com/tests/thyroid-complete-panel) | Panel (4 tests) | $109.99 | $115.99 | No | 3–7 business days |
| [Pre-Diabetes Panel](https://www.test-well.com/tests/pre-diabetes-panel) | Panel (5 tests) | $89.99 | $95.99 | Yes | 2–5 business days |
| [TSH (Thyroid Stimulating Hormone)](https://www.test-well.com/tests/tsh) | Test | $26.99 | $32.99 | No | 1–3 business days |
| [Hemoglobin A1c](https://www.test-well.com/tests/hemoglobin-a1c) | Test | $21.99 | $27.99 | No | 2–4 business days |
| [Insulin, Fasting](https://www.test-well.com/tests/insulin-fasting) | Test | $22.99 | $28.99 | Yes | 2–4 business days |
| [Glucose, Fasting](https://www.test-well.com/tests/glucose-fasting) | Test | $24.99 | $30.99 | Yes | 1–3 business days |
| [Lipid Panel](https://www.test-well.com/tests/lipid-panel) | Test | $24.99 | $30.99 | Yes | 1–3 business days |
| [Cortisol (AM)](https://www.test-well.com/tests/cortisol-am) | Test | $26.99 | $32.99 | No | 2–4 business days |

Prices are cash-pay; every order adds one $6.00 lab processing fee. Physician authorization included.

## 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.

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- [Which blood tests are used for unexplained weight loss?](https://www.test-well.com/symptoms/unexplained-weight-loss)
- [All symptoms](https://www.test-well.com/symptoms)
- [Browse by condition](https://www.test-well.com/conditions)

---

Medically reviewed by Youmna DiStefano, MD (Medical Reviewer, TestWell); last reviewed 2026-09-06. Review policy: https://www.test-well.com/editorial-policy

Canonical page: https://www.test-well.com/symptoms/weight-gain
Machine-readable catalog: https://www.test-well.com/api/catalog.json · MCP server: https://www.test-well.com/mcp · Overview for agents: https://www.test-well.com/llms.txt

Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.