Tired all the time: what you can check in your blood

Fatigue rarely has a single cause. Sleep, stress and load are almost always part of it. But a handful of blood values do tend to move with how you feel, and those you can simply measure.

A blood test will not explain your fatigue. What it does is rule out or reveal a number of common contributors, so you know where to look next. That is useful information, including when everything falls inside the reference range.

The markers that matter most here

Iron status: ferritin, iron, transferrin and saturation

Ferritin is your iron store. It can be low while your haemoglobin is still fine, so a normal blood count does not rule out a depleted store. See iron and ferritin.

Vitamin B12 and folate

Both are needed for red blood cell production and for your nervous system. Relevant if you eat few or no animal products, or use metformin or acid reducers. See vitamin B12.

Vitamin D

At this latitude almost nobody produces enough vitamin D through the skin between October and April. See vitamin D.

Thyroid: TSH, fT4 and fT3

The thyroid partly sets your metabolic pace. TSH alone gives an incomplete picture, which is why fT4 and fT3 are included. See thyroid.

Blood sugar and blood count

Fluctuating blood sugar causes energy dips, especially after meals. HbA1c shows the average over roughly three months. The full blood count shows anaemia and the shape and size of your red cells.

All markers at a glance

Which package fits

Worth knowing up front

A normal result does not mean your symptoms are not real. Reference ranges describe the spread in a population, not how someone feels. You can sit inside the range and still be at the low end of it. That is what this article is about.