Fatigue is the symptom with the longest list of causes, which is exactly why a focused blood panel helps. Most persistent, unexplained tiredness traces back to a short list of correctable culprits: low iron, a sluggish thyroid, a vitamin shortfall, or blood sugar that is quietly off.
If you are tired in a way that rest does not fix, these are the markers worth checking before you assume it is just stress or age.
Your iron stores. Low iron, even without full anemia, is one of the most common and most missed causes of fatigue, especially in menstruating women.
The first thyroid test. An underactive thyroid is a leading medical cause of persistent tiredness, weight gain, and low mood.
Read with TSH, it confirms how much thyroid hormone you are actually making.
Low B12 causes fatigue, brain fog, and nerve symptoms, and is common in older adults and anyone eating little animal food.
Deficiency is widespread and a classic cause of low energy, low mood, and aches.
Blood sugar that swings is an underrated energy drain, so a metabolic check belongs in any fatigue workup.
A complete read of the thyroid, paired with the most common non-thyroid causes of the very same symptoms. When you are tired, foggy, or cold, this panel separates a thyroid problem from the iron and B-vitamin shortfalls that feel identical.
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The encouraging part is that the common causes of fatigue are mostly fixable once you can see them. A low ferritin or vitamin D is a far better answer than no answer at all.