Tired all the time? Here is what a blood test shows

Iron deficiency is the most common measurable cause

Iron deficiency develops slowly. First, the body's iron stores are depleted, visible as low ferritin, and only later does haemoglobin (Hb) drop, leading to anaemia. This means you can be tired, cold, and short of breath on stairs long before the haemoglobin (Hb) level looks abnormal. Therefore, it is not enough to only measure haemoglobin (Hb) – ferritin must be included.

Iron deficiency is particularly common in menstruating women, pregnant women, vegetarians, and people who exercise heavily. In men and post-menopausal women, newly discovered iron deficiency should always be investigated further, as the cause may be in the gastrointestinal tract.

The thyroid controls the body's pace

An underactive thyroid causes fatigue, sensitivity to cold, weight gain, dry skin, and low mood. TSH is the test that catches this first: when the thyroid produces too little hormone, TSH rises before symptoms become obvious. Thyroid disorders are significantly more common in women and become more frequent with age.

Vitamins, blood sugar and inflammation

Vitamin B12 deficiency causes fatigue, concentration difficulties, and sometimes tingling in the hands and feet. The risk is increased with a vegetarian or vegan diet, advanced age, gastric diseases, and long-term treatment with metformin or acid blockers.

Vitamin D deficiency is common in the UK/Sweden during the winter and can contribute to fatigue and muscle aches. HbA1c shows the average blood sugar over the last two to three months; both high and fluctuating levels can cause fatigue. CRP shows if there is ongoing inflammation or infection in the body.

When the blood test is normal

Often, all values are normal. This is an important message in itself: it argues against iron deficiency, anaemia, thyroid disease, vitamin deficiency, and undiagnosed diabetes. In such cases, it is reasonable to look at sleep, stress, exercise, alcohol, and mental health instead.

A blood test does not replace a medical assessment. If you have severe or rapidly increasing fatigue, involuntary weight loss, fever, or other clear symptoms, you should contact healthcare services or 11177.