What are erythrocytes?
A red blood cell is a disc without a nucleus, packed with haemoglobin, that circulates for about four months and is then broken down in your spleen. Your bone marrow makes millions of new ones every second, driven by a hormone from your kidneys that responds to how much oxygen your tissues get. This value counts how many of those cells there are per litre of blood, in ×10¹²/L, so in trillions per litre. The count is one of three numbers that together describe your oxygen transport. Haemoglobin says how much oxygen carrier there is per litre, haematocrit what share of the blood is cells, and the red cell count how many cells that is spread over. From those three follow the cell size and the filling per cell, and that is where the count gains its meaning: many small, pale cells is iron deficiency, few large cells is a deficiency of B12 or folate. Normal is about 4.6 to 5.5 ×10¹²/L for a man from age 19 and 4.2 to 5.0 ×10¹²/L for a woman from age 19. The count is a concentration, so your fluid balance counts: thickened blood gives a higher number without a cell being added.
Why are erythrocytes relevant?
On its own the red cell count is rarely the value you read something from; haemoglobin says more directly whether you have anaemia. The count becomes interesting in combination. A low haemoglobin with a normal or high number of cells means the cells are small and pale, and that is the handwriting of iron deficiency, or of thalassaemia trait, in which the count is actually high with a low haemoglobin. A low haemoglobin with a low number of large cells is B12 or folate. So the count helps tell the two most common kinds of anaemia apart before anything further is measured. For anyone who does sport the count is a measure of adaptation. Early in a training block the count looks lower because your blood volume grows, not because there are fewer cells; at altitude it rises after a few weeks because the marrow works harder. Both are normal. In doping control the red cell count, the haematocrit and the reticulocytes are for that reason the fixed values of the blood passport. The other side is usually harmless: a high count is nine times out of ten from drinking too little. Smoking and sleep apnoea are the two reasons that keep a high count up for years, because the body makes extra cells to compensate for oxygen that is missing at night or through carbon monoxide. Both can be reversed.
Erythrocytes reference ranges
What counts beside the number:
- Haemoglobin, which says more directly whether you have anaemia
- MCV, because small cells are iron and large cells are B12 or folate
- Haematocrit, which together with the count yields the cell size
- Ferritin and RDW, which confirm a deficiency or give it away early
- How much you drank, whether you trained hard and whether you were at altitude
- Whether you smoke, and whether you snore and wake tired
The band above is where the labs overlap; the upper limit in particular differs per lab. The count is a concentration, so drinking too little or hard exertion lifts it and the large blood volume of endurance athletes pushes it down, without anything being wrong with your cells. The count only means something beside haemoglobin and the cell size: many small cells with a low haemoglobin is a different story from few large ones.
What Dutch labs actually use
4.2 – 5.0×10¹²/L
Between 4.0 and 4.20 and between 5.0 and 5.5 it depends on the lab, because each sets its limits on its own method and population. Above 5.5 every lab calls it abnormal.
every lab calls 4.2 – 5.0 ×10¹²/L normal. Between 4.0 and 4.20 and between 5.0 and 5.5 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Men from 16 yrs | 4.4–5.7 ×10¹²/L |
| Women from 16 yrs | 4.0–5.2 ×10¹²/L | |
| Star-shl2026 | Men 19+ | 4.60–6.20 ×10¹²/L |
| Women 19+ | 4.20–5.40 ×10¹²/L | |
| Certe2026 | Men from 18 yrs | 4.5–5.8 ×10¹²/L |
| Women from 18 yrs | 4–5.5 ×10¹²/L | |
| Clinical Diagnostics2026 | Men from 16 yrs | 4.5–5.5 ×10¹²/L |
| Women from 16 yrs | 4.0–5.0 ×10¹²/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Erythrocytes high or low: what it means
A low count means fewer cells or more plasma. Usually it is the first and rarely the last: anaemia from a deficiency of iron, B12 or folate; blood loss; a larger plasma volume in endurance athletes and in pregnancy; and reduced kidney function, because the kidney makes the hormone that drives the marrow. Look at haemoglobin and MCV: small cells point at iron and ferritin, large cells at B12 and folate, and a normal haemoglobin with a low count is in an athlete usually the blood volume. A high count means thickened blood or more cells. Dehydration is the most common reason; drink normally and have blood drawn again. If it stays high, time at altitude, smoking and sleep apnoea are the usual explanations. A high number of small cells with a low-normal haemoglobin fits thalassaemia trait, and that is good to know but not a disease. Only a persistently high count with plenty of white cells and platelets too belongs to a rare bone marrow condition. What you do about it: with a deficiency you top up iron, B12 or folate and see the count rise within weeks; with a low count from training you do nothing. With a high count you drink normally, and if you smoke, stopping is the lever. The count belongs beside haemoglobin, haematocrit and MCV, and beyond that beside ferritin and RDW. Have blood drawn normally hydrated, rested and not after hard exertion.
What lowers it
Fewer cells, or more plasma.
| Cause | How often |
|---|---|
| AnaemiaFrom a deficiency of iron, B12 or folate, or from a chronic disease; the cell size and ferritin say which | Often |
| Blood lossHeavy periods, or unnoticed from stomach or gut; the plasma is refilled faster than the cells | Often |
| Expanded plasma volumeEndurance training and pregnancy let the plasma grow faster than the cells; the count per litre falls while the transport is fine | Often |
| Reduced kidney functionThe kidney makes the hormone that drives the marrow; if it works less, fewer cells are added | Sometimes |
What raises it
Thickened blood, or a body making more cells because it is short of oxygen.
| Cause | How often |
|---|---|
| DehydrationToo little drunk, plenty sweated or just trained hard; the plasma shrinks and the count per litre rises without a cell being added | Often |
| Time at altitudeThin air sets the marrow to making more cells; after a few weeks at altitude the count sits higher | Sometimes |
| SmokingCarbon monoxide occupies part of the oxygen carrier and the body makes more cells to compensate | Sometimes |
| Sleep apnoeaNight-time oxygen dips drive production up; snoring and waking tired belong with it | Sometimes |
| Bone marrow diseaseSuch as polycythaemia; rare, and then the white cells and platelets usually rise too | Rare |
How does an erythrocytes blood test work?
- Referral
- Not needed. The red cell count is in every blood count you can have measured yourself.
- Fasting
- Not needed, but drink normally, because thickened blood gives a higher count.
- When
- Rested, not just after hard exertion and not in the weeks after time at altitude if you want to know your usual value.
- The draw
- One tube of blood from a vein in your arm, the same tube as for the rest of your blood count.
- Repeating
- Together with haemoglobin, a month after starting iron, B12 or folate; with a high count after a few days of drinking normally.
- Which test
- Erythrocytes 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 are erythrocytes?
Your red blood cells: discs without a nucleus, packed with haemoglobin, that carry oxygen from your lungs to your tissues. They last about four months, and your bone marrow makes millions of new ones every second. This value counts how many circulate per litre of blood. The count on its own says less than the combination with your haemoglobin and your cell size.
What is a normal erythrocyte count?
About 4.6 to 5.5 ×10¹²/L for a man from age 19 and 4.2 to 5.0 ×10¹²/L for a woman from age 19, where the labs overlap; the upper limit differs per lab. More important than where you sit in the band is whether the count fits your haemoglobin and your cell size.
What does a low red blood cell count mean?
Fewer cells or more plasma. If haemoglobin falls with it, it is anaemia: small cells point at iron, large ones at B12 or folate, and blood loss or kidneys working less are the other reasons. If you train a lot or are pregnant, it is often your blood volume that has grown, and that is not a deficiency. Ferritin and MCV tell the difference.
What does a high red blood cell count mean?
Usually blood thickened by drinking too little; drink normally and have blood drawn again. If it stays high, your body is making extra cells because it is short of oxygen: time at altitude, smoking or sleep apnoea. Many small cells with a low-normal haemoglobin fits thalassaemia trait, which is good to know but not a disease. Rare is a bone marrow condition, and that stands out because the white cells and platelets rise too.
Why does the count say less than haemoglobin?
Because it is not the number of cells that decides how much oxygen your blood carries, but the amount of haemoglobin in them. Many small, pale cells carry less than few well-filled ones. Haemoglobin measures the carrier itself; the count says how that carrier is spread over the cells, and that only becomes informative in combination with the cell size.
What does a high number of small cells mean?
With a low-normal haemoglobin and a normal ferritin it fits thalassaemia trait: an inherited feature in which the cells are small and the marrow compensates with more cells. It is not a disease and needs no treatment, but it is good to know, because it looks like iron deficiency and iron does not help then. Ferritin tells the difference.
What do sport and altitude do to the count?
Endurance training enlarges your plasma volume, so the count per litre looks lower while there are not fewer cells; that is an adaptation. Altitude does the opposite: after a few weeks in thin air the marrow has made more cells and the count sits higher, which lasts for weeks. In doping control the red cell count, the haematocrit and the reticulocytes are fixed values for that reason.
Do I need to fast for an erythrocyte test?
No, but drink normally and have blood drawn rested and not after hard exertion, because thickened blood gives a higher count. It comes from the same tube as your whole blood count, so haemoglobin, haematocrit and MCV sit beside it automatically.
Which tests include erythrocytes?
Erythrocytes 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.Unilabs, test catalogue (Dutch): erythrocytes. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): erythrocytes. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): erythrocytes. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): erythrocytes. 2026. clinicaldiagnostics.nl
- 5.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
- 6.NHG guideline on anaemia (M76), Dutch College of General Practitioners. 2024. richtlijnen.nhg.org
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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