Feeling tired all the time isn't normal - it's a symptom. The right blood tests can help identify why your energy is depleted.
Common Causes of Low Energy
- Iron deficiency (with or without anemia)
- Thyroid dysfunction
- B12 deficiency
- Vitamin D deficiency
- Blood sugar problems
- Chronic inflammation
- Poor sleep quality
The Energy Panel
Iron Status
- Ferritin (most important)
- Serum iron
- TIBC
- Transferrin saturation
- CBC
Thyroid
- TSH
- Free T3 (the active hormone)
- Free T4
- Thyroid antibodies
Vitamins
- Vitamin B12
- Vitamin D
- Folate
Metabolic
- Fasting glucose
- HbA1c
- Fasting insulin
Inflammation
- CRP
- Ferritin (also elevated in inflammation)
The Most Missed Tests
Doctors often skip:
- Ferritin: Checked only if CBC is abnormal
- Free T3: Only TSH is checked
- Fasting insulin: Only glucose is checked
These are often the most revealing tests for unexplained fatigue.
When Results Are "Normal"
If all results are normal but you're still tired:
- Look at optimal vs. normal ranges
- Consider additional testing (cortisol, sex hormones)
- Evaluate sleep quality
- Assess stress levels
References
- Vaucher, P., et al. (2012). Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. Canadian Medical Association Journal, 184(11), 1247-1254.
- Stabler, S. P. (2013). Clinical practice: vitamin B12 deficiency. New England Journal of Medicine, 368(2), 149-160.
