What Labs to Check If You're Always Tired
Fatigue is one of the most common complaints, and blood tests can identify many treatable causes. Here's what to ask your doctor to check.
Educational Information Only
This guide is for educational purposes and does not constitute medical advice. Fatigue can have many causes, including conditions that blood tests cannot detect (sleep disorders, depression, chronic fatigue syndrome). Always consult a healthcare provider for proper evaluation and diagnosis.
Primary Labs to Request
Thyroid Panel (TSH, Free T4, Free T3)
ThyroidHypothyroidism is one of the most common and treatable causes of fatigue. Even subclinical hypothyroidism (normal T4, elevated TSH) can cause tiredness.
Prevalence: About 5% of Americans have hypothyroidism, and fatigue is the #1 symptom.
Iron Studies (Ferritin, Iron, TIBC)
IronIron deficiency is the most common nutritional deficiency worldwide. You can be iron deficient WITHOUT being anemic - ferritin drops before hemoglobin does.
Prevalence: Iron deficiency affects ~10% of women in the US.
Complete Blood Count (CBC)
BloodAnemia (low hemoglobin) directly causes fatigue because your blood carries less oxygen. The CBC also reveals MCV, which helps identify the type of anemia.
Prevalence: Anemia affects about 3 million Americans.
Vitamin B12
VitaminsB12 deficiency causes fatigue, weakness, and neurological symptoms. Common in vegetarians/vegans, older adults, and those on metformin or PPIs.
Prevalence: Up to 15% of people over 60 are B12 deficient.
Vitamin D
VitaminsLow vitamin D is associated with fatigue, muscle weakness, and depression. Deficiency is extremely common, especially in northern latitudes.
Prevalence: About 42% of US adults are vitamin D deficient.
Glucose & Hemoglobin A1c
MetabolicBoth high blood sugar (diabetes) and low blood sugar (hypoglycemia) cause fatigue. Undiagnosed diabetes often presents as unexplained tiredness.
Prevalence: 37 million Americans have diabetes; 96 million have prediabetes.
Comprehensive Metabolic Panel (CMP)
Organ FunctionKidney disease, liver disease, and electrolyte imbalances can all cause fatigue. A CMP screens for these conditions.
Prevalence: 37 million Americans have chronic kidney disease; most don't know it.
Additional Tests (If Primary Labs Normal)
Important: Normal Labs Don't Rule Out Everything
If all your labs come back normal, don't give up. Many causes of fatigue aren't detected by blood tests:
- • Sleep apnea — requires a sleep study
- • Depression/anxiety — mental health evaluation
- • Chronic fatigue syndrome — diagnosis of exclusion
- • Medication side effects — review with pharmacist
- • Poor sleep hygiene — sleep quality matters
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