What is hemoglobin?
Every red blood cell is full of haemoglobin, a protein with iron at its core that binds oxygen in your lungs and releases it again in your tissues. Your haemoglobin value is the amount of that protein per litre of blood, and with that the capacity of your oxygen transport: how much your muscles and brain get delivered per heartbeat. It is the value that defines anaemia, and the value that helps decide your endurance. Haemoglobin says how much capacity you have, not why it is too low or too high. For that you read it beside the other values from the same tube: the cell size, MCV, which becomes small in iron deficiency and large in a deficiency of B12 or folate, and beside ferritin, your iron store. That store runs empty months before haemoglobin falls; a normal haemoglobin therefore does not rule out an early iron deficiency. Your report shows haemoglobin in mmol/L. Normal is about 8.5 to 11.0 mmol/L for men and 7.5 to 10.0 mmol/L for women, and this is one of the few values the labs agree on exactly. It is a concentration, so your fluid balance counts too: thickened blood gives a higher number without there being more cells.
Why is hemoglobin relevant?
Haemoglobin is what you feel when you walk up the stairs. If it falls, every muscle gets less oxygen per heartbeat, and you notice that as tiredness that does not pass, breathlessness on exertion, a faster heart rate, dizziness on standing, paleness and slower recovery after sport. It is the last step of an iron deficiency, and usually the store has been empty for months by then. Anyone tired with a low haemoglobin almost always has a reason that can be found and reversed, and the most common is iron: heavy periods, too little iron from food, or blood loss you do not see. For anyone who does sport, haemoglobin is the value behind endurance, and at the same time a value with a pitfall. Endurance training enlarges your blood volume: more plasma is added than cells, and the haemoglobin per litre dips a fraction while your total oxygen transport is actually larger. That is an adaptation, not anaemia, and you tell the difference with ferritin. An athlete with a low-normal haemoglobin and a normal ferritin is fit; an athlete with a low-normal haemoglobin and an empty ferritin is running on an empty tank. The high side is usually not a problem. Drinking too little thickens the blood and lifts the number; altitude, smoking and sleep apnoea set the body to making more red cells because too little oxygen comes in at night or in thin air. Smoking is the lever you have yourself there: carbon monoxide occupies part of your haemoglobin, and your body makes more to compensate. Only a persistently high value without one of those explanations belongs to a rare bone marrow condition, and that stands out because the white cells and platelets rise too.
Hemoglobin reference ranges
What counts beside the number:
- MCV from the same tube: small cells are iron, large ones are B12 or folate
- Ferritin, because the store runs empty months before haemoglobin falls
- Haematocrit and the red cell count, which should move with the haemoglobin
- Reticulocytes, which show whether the marrow responds
- How much you drank, whether you trained hard and whether you were at altitude
- Whether you smoke, and whether you snore and wake tired
Haemoglobin is one of the few values the labs agree on exactly, and the band for women sits lower than that for men. In the Netherlands it is in mmol/L, internationally in g/dL; convert with 1 mmol/L is about 1.61 g/dL. In pregnancy the limits sit lower and shift per trimester, because the plasma volume grows faster than the number of cells. Haemoglobin says whether you have anaemia; ferritin and the cell size say why.
What Dutch labs actually use
7.5 – 10.0mmol/L
Outside this range every lab calls it abnormal.
every lab calls 7.5 – 10.0 mmol/L normal. Outside that range every lab calls it abnormal.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Men 15+ | 8.5–11.0 mmol/L |
| Women 15+ | 7.5–10.0 mmol/L | |
| Star-shl2026 | Men 18+ | 8.5–11.0 mmol/L |
| Women 18+ | 7.5–10.0 mmol/L | |
| Certe2026 | Men 18+ | 8.5–11.0 mmol/L |
| Women 18+ | 7.5–10.0 mmol/L | |
| Clinical Diagnostics2026 | Men 11+ | 8.5–11.0 mmol/L |
| Women 11+ | 7.5–10.0 mmol/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Hemoglobin high or low: what it means
A low haemoglobin means anaemia, and the question is of which kind. From common to rare: an iron deficiency, blood loss, a larger plasma volume in endurance athletes and in pregnancy, a deficiency of vitamin B12 or folate, and a chronic inflammation or kidney disease. The cell size points the way: small cells are iron, large cells are B12 or folate, normal cells are blood loss, inflammation or the kidneys. Ferritin confirms the iron, and in a man or a woman after the menopause blood loss in the gut is the first place to look. A high haemoglobin is usually thickened blood: too little drunk, sweated, or drawn after a hard effort. Drink normally and have blood drawn again, and the value usually sits back within the band. If it stays high, smoking, sleep apnoea and time at altitude are the usual reasons; smoking you leave, sleep apnoea you have investigated. A high haemoglobin with plenty of white cells and platelets too is the rare picture that asks for further investigation of the bone marrow. What you do about it: with an iron deficiency you refill the store with red meat, fish, legumes and green vegetables with vitamin C alongside, and where needed an iron tablet every other day. Haemoglobin then rises within weeks, about half a mmol/L per week, and the symptoms lift with it. With a deficiency of B12 or folate topping up works just as fast. For an athlete with a normal ferritin there is nothing to do, except keep training. Set haemoglobin beside MCV and ferritin, and beyond that beside haematocrit, the red cell count and the reticulocytes, which show whether the marrow responds. Have blood drawn well hydrated and not after hard exertion, and compare over time at the same time of day.
What lowers it
Too little oxygen transport, usually from a deficiency or from loss.
| Cause | How often |
|---|---|
| Iron deficiencyThe most common reason; the store has then been empty for months, the cells become small and ferritin is low | Often |
| Heavy blood lossHeavy periods, or unnoticed from stomach or gut; in men and after the menopause the first place to look | Often |
| Expanded plasma volumeIn endurance athletes and in pregnancy more plasma is added than cells; the number per litre dips while the transport is fine | Often |
| Vitamin B12 or folate deficiencyThe marrow then cannot make DNA and delivers few, too large cells; with plant-based eating, antacids and few vegetables | Sometimes |
| Chronic inflammation or kidney diseaseAn inflammation holds on to iron and the kidney makes less of the hormone that drives the marrow; the cells stay normal in size | Sometimes |
What raises it
Usually thickened blood, and otherwise a body adapting to too little oxygen.
| Cause | How often |
|---|---|
| DehydrationLess plasma lets the concentration rise without there being more cells; drinking and drawing again settles it | Often |
| Living or training at altitudeThin air sets the marrow to making more red cells; the effect lasts weeks after returning | Sometimes |
| SmokingCarbon monoxide occupies part of your haemoglobin and the body makes more to compensate; stopping lets the value fall | Sometimes |
| Sleep apnoeaNight-time oxygen dips drive production up; snoring, waking tired and a high haemoglobin belong together | Sometimes |
| Bone marrow diseaseSuch as polycythaemia; rare, and then the white cells and platelets usually rise too | Rare |
How does a hemoglobin blood test work?
- Referral
- Not needed. Haemoglobin is in every blood count you can have measured yourself.
- Fasting
- Not needed, but drink normally, because thickened blood gives a higher number.
- When
- Not just after hard exertion or a day of drinking little, and always at the same time of day if you follow a trend.
- Which test
- Hemoglobin is in the Iron & fatigue test (€99) and in .
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is haemoglobin?
The protein in your red blood cells that binds oxygen in your lungs and releases it in your tissues. It gives blood its red colour and has iron at its core, and the oxygen hooks onto that iron. Your haemoglobin value is how much of that protein sits in a litre of blood, and with that how much oxygen your blood can carry. It is a concentration, so your fluid balance counts in the number too.
What is a normal haemoglobin level?
About 8.5 to 11.0 mmol/L for men and 7.5 to 10.0 mmol/L for women, and this is one of the few values the labs agree on exactly. Below that it is called anaemia. For anyone who does sport it also matters where in the band you sit: at the high end your blood carries more oxygen per litre.
What does a low haemoglobin mean?
Anaemia: your blood carries too little oxygen, and you feel that as tiredness, breathlessness on the stairs, a faster heart rate and slower recovery. The most common reason is an iron store that has been empty for months, from periods, too little iron from food or blood loss you do not see. After that a deficiency of B12 or folate, and a chronic inflammation or kidney disease. The cell size and ferritin say which it is, and almost every kind can be reversed.
What does a high haemoglobin mean?
Usually thickened blood: too little drunk, plenty sweated or drawn after hard exertion. Drink normally and have blood drawn again. If the value stays high, it is a body adapting to too little oxygen: time at altitude, smoking or sleep apnoea. Rare is a bone marrow condition that makes too many red cells, and that stands out because the white cells and platelets rise too.
Why do endurance athletes have a lower haemoglobin?
Because endurance training enlarges the blood volume: more plasma is added than cells, and the haemoglobin per litre dips a fraction while the total oxygen transport is actually larger. That is an adaptation, not anaemia. You tell the difference with ferritin: if the store is normal, nothing is wrong; if it is empty, you are running on an empty tank and iron does help.
How do I raise my haemoglobin?
By removing the cause, and usually that is iron: red meat, fish, poultry, legumes and green vegetables with vitamin C alongside, and with an empty store an iron tablet every other day. Haemoglobin then rises about half a mmol/L per week and is clearly higher after a month; the store itself needs a few months longer. With a deficiency of B12 or folate topping up works just as fast. Smoking raises haemoglobin too, but for the wrong reason.
What does my fluid balance have to do with haemoglobin?
Everything, because it is a concentration. Drinking too little, sweating or a hard effort just before the draw let the plasma shrink and the number rise, without there being more cells. The other way round, drinking a lot or a larger blood volume dilutes the number. So have blood drawn normally hydrated, not after hard exertion, and always at the same time of day if you follow a trend.
Do I need to fast for a haemoglobin test?
No. Haemoglobin barely moves with food, but it does with fluid: drink normally and do not have blood drawn after hard exertion. It comes from the same tube as your whole blood count, so MCV, haematocrit and the red cell count sit beside it automatically, and ferritin comes from the same draw.
Which tests include hemoglobin?
Hemoglobin is in the Iron & fatigue test (€99, also as an add-on for €15), in the Biological age test (€69, also as an add-on for €15), in the comprehensive test (€229) and in .
Related biomarkers
Read on
Sources
- 1.NHG guideline on anaemia (M76), Dutch College of General Practitioners. 2024. richtlijnen.nhg.org
- 2.WHO, Guideline on haemoglobin cutoffs to define anaemia in individuals and populations. 2024. who.int
- 3.Unilabs, test catalogue (Dutch): haemoglobin. 2026. bepalingenklapper.nl
- 4.Star-shl, test catalogue (Dutch): haemoglobin. 2026. star-shl.nl
- 5.Certe, test catalogue (Dutch): haemoglobin. 2026. bepalingenwijzer.certe.nl
- 6.Clinical Diagnostics, lab guide (Dutch): Hb and MCV. 2026. clinicaldiagnostics.nl
- 7.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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