Symptom → lab tests
What blood tests are used for muscle weakness?
Short answer
Muscle weakness with no obvious cause is checked with creatine kinase (muscle breakdown), a comprehensive metabolic panel (electrolytes, kidney and liver), magnesium, vitamin D, TSH and morning cortisol. Statins and other medications are a frequent culprit, so the medication list matters as much as the labs.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
When should you see a clinician instead of ordering a test?
- Sudden weakness on one side, facial droop or trouble speaking — call emergency services
- Weakness that is spreading, trouble swallowing or breathing, or dark (cola-colored) urine — seek care the same day
Why these tests for muscle weakness?
Creatine kinase rises when muscle fibers are damaged — by statins, intense exercise, injury or inflammatory muscle disease. Low potassium, sodium, calcium or magnesium cause weakness and cramps, and the CMP catches most of them. Vitamin D deficiency produces proximal weakness (rising from a chair), thyroid disease in either direction causes weakness, and adrenal insufficiency — rare — is screened with morning cortisol.
Which conditions do these tests help evaluate?
- Chronic Fatigue — Thyroid, iron, B12, vitamin D and inflammation markers for persistent tiredness.
- Thyroid Problems — TSH, Free T4/T3 and antibodies to evaluate an under- or over-active thyroid.
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 |
|---|---|---|---|---|
| Fitness & Performance PanelSaves $99.93 vs ordering the tests separately | Panel · 8 tests | $119.99 | Yes | 2–5 business days |
| General Wellness PanelSaves $6.97 vs ordering the tests separately | Panel · 4 tests | $89.99 | Yes | 1–3 business days |
| Creatine Kinase (CK) | Test | $18.99 | No | 1–3 business days |
| Comprehensive Metabolic Panel | Test · 14 biomarkers | $22.99 | Yes | 1–3 business days |
| Magnesium | Test | $19.99 | No | 2–4 business days |
| Vitamin D, 25-Hydroxy | Test | $41.99 | No | 1–3 business days |
| TSH (Thyroid Stimulating Hormone) | Test | $26.99 | No | 1–3 business days |
| Cortisol (AM) | Test | $26.99 | No | 2–4 business days |
Common questions
Should I stop exercising before a CK test?
Avoid strenuous exercise for 48 hours before the draw; hard workouts raise CK for days and can mimic a muscle problem.
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.