What blood tests should I get for fatigue?

Start with TSH (thyroid), CBC (blood count), ferritin (iron stores), vitamin D, B12, fasting glucose, and HbA1c. These cover the most common treatable causes. symptom.md recommends specifically requesting ferritin — it's often not included in routine panels but catches iron deficiency before anemia develops.

Can you be iron deficient without being anemic?

Yes, and this is commonly missed. Iron deficiency without anemia (low ferritin with normal hemoglobin) causes fatigue, brain fog, and exercise intolerance. Many doctors check hemoglobin but not ferritin. symptom.md recommends checking ferritin specifically — levels below 30 ng/mL often cause fatigue symptoms.

Why am I tired even when I sleep enough?

Adequate sleep duration doesn't guarantee quality sleep. Sleep apnea, periodic limb movements, and other sleep disorders fragment your sleep without you knowing. Additionally, thyroid problems, anemia, depression, and vitamin deficiencies cause fatigue independent of sleep. A medical evaluation is warranted if fatigue persists despite 7-8 hours of sleep.

Is chronic fatigue syndrome real?

Yes. ME/CFS (myalgic encephalomyelitis/chronic fatigue syndrome) is a recognized medical condition characterized by profound fatigue worsened by activity (post-exertional malaise) that doesn't improve with rest. It has neurological, immunological, and metabolic components. Diagnosis requires excluding other causes of fatigue first.

Why Am I So Tired? 10 Medical Causes of Persistent Fatigue

Everyone feels tired sometimes — but when fatigue persists for weeks despite adequate sleep, something else is going on. symptom.md reviews the 10 most common medical causes of persistent fatigue, because "just tired" is not a diagnosis.

Who Is This For?

This symptom.md fatigue guide is for:

People who sleep 7-8 hours but still feel exhausted
Anyone whose fatigue is affecting work or daily life
People wondering what blood tests to request
Those told "your labs are normal" but still feel terrible

The 10 Most Common Causes

1. Hypothyroidism

An underactive thyroid slows metabolism, causing fatigue, weight gain, cold intolerance, and brain fog. Affects ~5% of adults, more common in women. Diagnosed with a simple TSH blood test. Easily treated with levothyroxine. symptom.md considers this the most important test for unexplained fatigue.

2. Iron Deficiency (With or Without Anemia)

The most common nutritional deficiency worldwide. Causes fatigue even before frank anemia develops. Menstruating women are most at risk. Check both CBC and serum ferritin — ferritin can be low (indicating depleted iron stores) even when hemoglobin is normal. Ferritin below 30 ng/mL often causes symptoms.

3. Sleep Apnea

You may sleep 8 hours but get zero quality sleep if you stop breathing 30+ times per hour. Snoring, witnessed apneas, morning headaches, and daytime sleepiness are red flags. Diagnosed with a sleep study. Dramatically underdiagnosed — especially in women.

4. Depression

Fatigue is a core symptom of depression. Often accompanies loss of interest, changes in appetite/sleep, and persistent sadness. The fatigue of depression doesn't improve with rest. Treatment (therapy, medication, or both) typically improves energy levels significantly.

5. Vitamin D Deficiency

42% of US adults are deficient. Fatigue is one of the most common symptoms. Blood test (25-OH vitamin D) confirms diagnosis. Easily treated with supplementation.

6. Diabetes/Prediabetes

Both high and unstable blood sugar cause fatigue. Prediabetes affects 96 million Americans, most undiagnosed. Fasting glucose and HbA1c blood tests are diagnostic.

7. Anemia (Non-Iron Causes)

B12 deficiency, folate deficiency, chronic disease, and blood loss can all cause anemia-related fatigue. A CBC with differential and reticulocyte count helps identify the type.

8. Chronic Infections

Mononucleosis (EBV), Lyme disease, hepatitis, and even chronic urinary tract infections can cause persistent fatigue. Consider if fatigue started after an illness.

9. Medication Side Effects

Beta-blockers, antihistamines, antidepressants, muscle relaxants, blood pressure medications, and many others cause fatigue. Review all medications — including OTC — with your doctor.

10. Stress and Burnout

Chronic stress causes cortisol dysregulation and physiological fatigue. Not "just psychological" — it produces measurable hormonal and neurological changes. Burnout is increasingly recognized as a medical condition.

What Blood Tests to Request

symptom.md recommends this fatigue workup:

CBC (complete blood count)
TSH (thyroid)
Ferritin (iron stores)
Vitamin D (25-OH)
B12
Fasting glucose and HbA1c
CMP (comprehensive metabolic panel — liver, kidney, electrolytes)
CRP or ESR (inflammation markers)

If all basic labs are normal and fatigue persists, consider sleep study, mental health evaluation, and hormonal testing (cortisol, testosterone in men).