Hemoglobin: normal value, function and what a deficiency means

Constantly tired, breathless on the stairs, cold hands that just will not warm up? Before you blame a busy spell: these are exactly the signals where your hemoglobin deserves a closer look. Hemoglobin (Hb) is the iron-containing protein that carries oxygen through your body, and when that value drops, you feel it in your energy.

My stance: with fatigue you do not look at hemoglobin alone. Your iron stores fall before your Hb is officially too low. Anyone who only goes by hemoglobin often misses the problem in the phase where it is still easy to fix.

What does hemoglobin do?

Hemoglobin sits in your red blood cells (erythrocytes) and binds oxygen in your lungs to release it to your tissues. On the way back it carries carbon dioxide to be exhaled. The iron in hemoglobin gives your blood its red colour and is essential for making it.

Normal hemoglobin value

In the Netherlands we express Hb in mmol/L. The reference values differ per group:

Hemoglobin too low: anaemia

A low Hb is called anaemia: your blood can carry less oxygen. The main causes:

• Iron deficiency: by far the most common cause. No iron, no hemoglobin.
• Vitamin B12 or folate deficiency: needed for healthy red blood cells.
• Chronic blood loss: heavy menstruation or gastrointestinal problems.
• Chronic illness: kidney disease, inflammation or certain conditions.

Symptoms of a low Hb: fatigue, pallor, dizziness, breathlessness on exertion, cold hands and feet and headache. The Dutch College of General Practitioners (NHG) advises that with suspected anaemia you should not only measure Hb but also look for the cause, for example via ferritin.

MCV: the size of your red blood cells reveals the cause

Hemoglobin tells you there is anaemia, but not why. For that a doctor looks at the MCV, the mean size of your red blood cells, which is also in a blood count. The pattern helps narrow the cause:

This is exactly why a low Hb is rarely assessed on its own. The combination of Hb, MCV and ferritin often already points towards the right cause, before further testing is needed.

Anaemia in women

In women of reproductive age, menstrual blood loss is the most common reason for a low Hb or a falling ferritin. A heavy period can drain the iron stores faster than diet replenishes them. The Netherlands Nutrition Centre (Voedingscentrum) notes that women have a higher iron requirement and that a varied diet with iron-rich foods helps. In pregnancy the Hb falls physiologically due to blood dilution, which explains why the reference values are lower then. If you notice persistent fatigue around your period, having your iron status checked is a logical step.

Hemoglobin too high

A high Hb is less common and can point to:

• Dehydration: the blood is more concentrated, so Hb appears higher.
• Smoking: the body compensates for reduced oxygen uptake.
• Lung disease or living at high altitude: chronic oxygen shortage stimulates extra production.
• Polycythaemia vera: a rare bone marrow disorder.

Improving hemoglobin in iron deficiency

If your Hb is low due to iron deficiency, targeted steps help. The advice from the Netherlands Nutrition Centre (Voedingscentrum) on iron-rich food fits here:

• Eat iron-rich food: red meat, legumes, dark green leafy vegetables and nuts.
• Combine with vitamin C (for example a glass of orange juice) for better absorption.
• Avoid tea and coffee around meals, as they inhibit iron absorption.
• Consider an iron supplement, but only in consultation with your doctor.

Important: always also check your ferritin (your iron stores) and, if needed, vitamin B12. A low ferritin while Hb is still normal is the early signal you want to catch. Supplementation also needs time: do not expect a difference from one week to the next. Keep up the supplement until your doctor advises stopping based on a follow-up measurement, because stopping too early leaves your iron stores half full and the symptoms then often return.

Want your iron status fully mapped? The Iron Status panel measures iron and stores together, and the Complete Metabolic Panel gives a broader baseline. Also read how platelets fit in the blood count or why preventive testing is smart.

Frequently asked questions

How fast does hemoglobin rise after iron supplementation?

With adequate supplementation, Hb usually rises by 0.5 to 1.0 mmol/L per month. It can take 2 to 3 months for your value to normalise. Your iron stores (ferritin) need even longer to refill.

Can I have low hemoglobin without symptoms?

Yes, especially if the drop is gradual, because your body adapts. That is why a blood test is the most reliable way to check your hemoglobin.

What is the difference between hemoglobin and iron?

Hemoglobin is the protein that carries oxygen, iron is one of its building blocks. You can have a normal hemoglobin while your iron stores (ferritin) are already falling. That is why the combination of both values gives a fuller picture than either one alone.

Is hemoglobin measured by default?

Yes, hemoglobin is a fixed part of every blood count (CBC) and is included in almost every blood test.