Low Energy? Blood Tests That Can Help Explain Why

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.