Anaemia and Breathlessness: The Cause Found by a Simple Blood Test

Perfect lungs, normal oxygen saturation, and genuinely insufficient oxygen delivery. It happens more often than people expect.

Why saturation misleads here

This is the crucial point and it explains why anaemia gets missed in people who have already checked their oxygen levels.

Oxygen saturation measures the percentage of available haemoglobin binding sites that are carrying oxygen. It says nothing about how much haemoglobin there is.

Someone with half the normal haemoglobin can have 98 percent saturation. Their haemoglobin is fully loaded; there is simply much less of it. Total oxygen delivered to tissue is dramatically reduced while the oximeter reads reassuringly normal.

So a normal pulse oximeter reading does not rule out an oxygen delivery problem, and breathlessness with normal saturation is a specific reason to check a blood count.

What the body does about it

Compensation for reduced oxygen-carrying capacity means increasing delivery by other means.

Cardiac output rises — higher heart rate and stroke volume — to move the reduced oxygen content around faster. Breathing rate increases, though this cannot help much since the problem is not oxygen uptake.

The subjective result is breathlessness on exertion, fatigue, palpitations, and reduced exercise tolerance. Exactly the presentation people attribute to being unfit or getting older.

Other signs worth noticing

• Fatigue disproportionate to activity, which is usually the earliest and most persistent symptom.
• Pallor, often most visible in the conjunctivae and palm creases.
• Palpitations or awareness of the heartbeat.
• Dizziness, particularly on standing.
• Headache.
• Cold hands and feet.
• Brittle nails, hair thinning, or spooning of the nails in iron deficiency.
• Restless legs, which has a recognised association with iron deficiency.
• Pica — craving ice or non-food substances — which is a specific and unusual sign of iron deficiency.
• Reduced exercise tolerance developing over months.

The common causes

Iron deficiency is the most common globally. Causes include blood loss — heavy menstrual bleeding, gastrointestinal bleeding — inadequate intake, and malabsorption including coeliac disease.

Vitamin B12 or folate deficiency, producing a different pattern on the blood count. B12 deficiency can also cause neurological symptoms and has additional causes including pernicious anaemia and metformin use.

Chronic disease, including kidney disease which reduces erythropoietin production, and chronic inflammation which impairs iron utilisation.

Haemolysis, where red cells are destroyed prematurely.

Bone marrow disorders, less common but important.

The point about investigating the cause

This matters and is sometimes skipped.

In an adult, particularly a man of any age or a postmenopausal woman, iron deficiency without an obvious explanation requires investigation of the gastrointestinal tract. Occult blood loss from the gut is a common cause, and identifying its source can matter considerably.

Taking iron and feeling better without establishing why you were deficient can delay a diagnosis that needed making. A good clinician will investigate the cause rather than only correcting the number.

What to do

1. Ask for a full blood count. Inexpensive, routine, and definitive for whether anaemia is present.
2. Ask for iron studies — ferritin, transferrin saturation — plus B12 and folate, since a normal haemoglobin can coexist with depleted iron stores.
3. Do not self-treat with iron before testing. Iron overload is harmful, and taking iron obscures the diagnostic picture.
4. Discuss the cause, not just the treatment.
5. If prescribed iron, expect it to take time — haemoglobin recovery takes weeks and replenishing stores takes months. Take it with vitamin C and away from tea, coffee, calcium and antacids, which all impair absorption.