Always Tired? What Blood Tests Can Tell You

1. CBC (Complete Blood Count)

Checks for anaemia: the most common cause of fatigue worldwide. Low haemoglobin means your blood is carrying less oxygen to your muscles and brain. Even mild anaemia (Hb 10–11 g/dL) causes significant fatigue.

2. Thyroid Profile (TSH)

An underactive thyroid (hypothyroidism) is extremely common, especially in women over 30. It causes fatigue, weight gain, hair loss, constipation and feeling cold. TSH above 4.0 mIU/L suggests hypothyroidism. Treatment with levothyroxine often brings energy levels back to normal.

3. Vitamin B12

B12 deficiency causes profound fatigue, along with tingling in hands/feet and memory problems. Extremely common in people following vegetarian or vegan diets. B12 below 200 pg/mL is deficient and needs treatment with supplements or injections.

4. Vitamin D

Deficiency is common worldwide, particularly in people with limited sun exposure, darker skin or covered dress. Symptoms include fatigue, muscle aches, bone pain and low mood. Vitamin D below 20 ng/mL is deficient and highly treatable with supplements.

5. Ferritin (Iron Stores)

Even without full anaemia, low ferritin (iron stores below 30 ng/mL) causes fatigue. This is especially common in women with heavy periods. Ferritin can be low when haemoglobin still appears normal, which is why ferritin must be tested separately.

6. Fasting Blood Sugar / HbA1c

Uncontrolled or undiagnosed diabetes causes fatigue because cells can't use glucose properly. Many people with Type 2 diabetes don't know they have it. A fasting sugar or HbA1c screens for this.

7. Liver Function Test (LFT)

Liver disease causes fatigue, especially fatty liver (NAFLD), which is increasingly common. Elevated SGPT/ALT is a common finding in people with unexplained tiredness and metabolic syndrome.