What are reticulocytes?
Red blood cells are made in your bone marrow and then live about four months in your blood. For the first day or two after leaving they still carry remnants of the production process, and in that phase they are called reticulocytes. After that they are ordinary red blood cells. Because that young phase is so short, the reticulocyte count is a snapshot of production: it says how many cells were added in the last few days, not how many are circulating in total. That makes the number different from your haemoglobin. Haemoglobin says whether you have anaemia; reticulocytes say why. A healthy marrow responds to anaemia by working harder, and then reticulocytes rise. If they stay low while haemoglobin is low, the marrow cannot work harder, usually because it lacks the raw materials: iron, vitamin B12 or folate. If they rise sharply, the marrow is producing at full tilt and the cells are disappearing elsewhere: through blood loss or through breakdown. Your report shows reticulocytes as a count per litre, ×10⁹/L, and sometimes as a per mille of all red blood cells. Normal is about 30 to 100 ×10⁹/L where the labs overlap. The per mille is a different measure and cannot be compared with that range.
Why are reticulocytes relevant?
The first reason to know your reticulocytes is that in anaemia they point the way. Tired, pale and a low haemoglobin can be many things, but with the reticulocytes beside it, it becomes one of two stories. Low: the marrow lacks raw materials or is being held back, and then you look in ferritin, B12, folate, your kidneys and an inflammation. High: the marrow is doing its job and blood is being lost or cells are being broken down, and then you look in the gut, the menstruation and the breakdown. That saves a detour. The second reason is that it is the fastest number in recovery. Start iron or vitamin B12 for a deficiency and reticulocytes rise within a week, long before haemoglobin moves. A rise is the sign that the deficiency was the cause and that the treatment is working; if the rise fails to come, something does not add up, and you want to know that after a week and not after three months. The third reason is sport. Anyone who trains or lives at altitude makes more red cells and has more reticulocytes; anyone who runs a lot breaks down some red cells with the impact of every footstrike and keeps up with a slightly raised count. Both are normal and belong to the picture. In doping control the reticulocyte count is, for that same reason, one of the fixed values in the blood passport.
Reticulocytes reference ranges
What counts beside the number:
- Haemoglobin from the same draw, because reticulocytes only mean something beside the question of whether you have anaemia
- MCV, because an iron deficiency makes the cells small and a B12 or folate deficiency makes them large
- Ferritin, vitamin B12 and folate, the raw materials of the marrow
- LDH and bilirubin, which rise when red cells are broken down
- Whether you have just started iron or B12, because then the count should be rising
- The unit on your report: a count per litre or a per mille
The band above is where the labs overlap, and the national table for general practice is slightly wider at both ends. The number is a count per litre; some reports also give a per mille of all red blood cells, and that is a different measure you do not compare with this band. More important than the band is the combination with your haemoglobin: a normal count with a low haemoglobin is already a marrow doing too little.
What Dutch labs actually use
The labs fall into two camps that differ a little at both ends: one uses 30 to 100 ×10⁹/L, the other 25 to 120 ×10⁹/L. For reading that matters little, because the question is rarely whether you sit just inside or just outside the band, but whether the count fits your haemoglobin: low while you have anaemia, or high while you recover.
30 – 100×10⁹/L
Between 25 and 30 and between 100 and 120 it depends on the lab, because each sets its limits on its own method and population. Above 120 every lab calls it abnormal.
every lab calls 30 – 100 ×10⁹/L normal. Between 25 and 30 and between 100 and 120 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | From 15 yrs | 30–100 ×10⁹/L |
| Star-shl2026 | Adults | 25–120 ×10⁹/L |
| Certe2026 | From 18 yrs | 30–100 ×10⁹/L |
| Clinical Diagnostics2026 | Adults | 25–120 ×10⁹/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Reticulocytes high or low: what it means
A low count means the marrow is releasing few new cells. With a normal haemoglobin that is rest and means nothing. With a low haemoglobin it is the clue that the marrow cannot work harder, in order of how often that occurs: an iron deficiency, a deficiency of vitamin B12 or folate, a chronic inflammation or kidney disease, medicines that suppress the marrow, and rarely a bone marrow disease. A high count means the marrow is working hard. With a low or falling haemoglobin that points at loss or breakdown: blood loss, usually from the gut or through heavy periods, or breakdown of red cells, in which LDH and bilirubin rise with it. With a recovering haemoglobin it is good news: the marrow is topping up, after a bleed or after starting iron or B12. With a normal or high haemoglobin it belongs to altitude, heavy endurance sport or a pregnancy. What you do about it: with a low count and anaemia, iron, B12 and folate are the first question, and the reticulocytes a week after starting are your check that it works. With a high count and anaemia the question is where the blood is going, and that question is not answered with diet. Read reticulocytes beside your haemoglobin and your MCV, and beyond that beside ferritin, vitamin B12, folate and LDH. Mind the unit: a count per litre and a per mille are two different numbers.
What lowers it
A marrow that cannot work harder, because it lacks raw materials or is being held back.
| Cause | How often |
|---|---|
| Iron deficiencyWithout iron no haemoglobin and no new cells; the most common reason for an anaemia with few reticulocytes, and within a week of starting iron they rise | Often |
| Vitamin B12 or folate deficiencyWithout B12 or folate the marrow cannot make DNA and the young cells get stuck; the red cells that do come are too large | Sometimes |
| Chronic inflammation or kidney diseaseAn inflammation holds on to iron and the kidney makes less of the hormone that drives the marrow; the marrow then works at half power | Sometimes |
| Medicines that suppress the marrowChemotherapy and a few drugs for rheumatism or autoimmune disease suppress production; reticulocytes fall first | Sometimes |
| Bone marrow diseaseA marrow that does not work itself; rare, and usually the white cells and platelets fall with it | Rare |
What raises it
A marrow working hard, because cells are being lost or because it is catching up on a deficiency.
| Cause | How often |
|---|---|
| Blood lossFrom the gut, through heavy periods or after surgery; the marrow tops up and reticulocytes rise within days | Often |
| Recovery after a bleed or treatmentAfter starting iron, B12 or folate for a deficiency reticulocytes rise within a week; that is the sign the treatment is working | Sometimes |
| Breakdown of red blood cellsIn haemolysis red cells are broken down too early, by antibodies, an inherited cell shape or a faulty heart valve; LDH and bilirubin rise with it | Sometimes |
| Living or training at altitudeThin air sets the marrow to making more red cells; heavy endurance sport and a pregnancy also lift the count slightly | Sometimes |
How does a reticulocytes blood test work?
- Referral
- Not needed. You can have reticulocytes measured yourself, preferably together with a blood count and ferritin.
- Fasting
- Not needed. The count does not move with food, but it does with altitude and with heavy exertion in the days before.
- The draw
- One tube of blood from a vein in your arm, the same tube as for your blood count; the lab counts the young cells with a dye that binds to their remnants.
- The result
- A single count in ×10⁹/L, sometimes with a per mille of all red blood cells beside it; the two are not interchangeable.
- Repeating
- A week after starting iron, B12 or folate to see whether the marrow responds; beyond that only when the haemoglobin gives reason to.
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What are reticulocytes?
The red blood cells your bone marrow released in the last day or two, which still carry remnants of the production process. After that they are ordinary red blood cells. The count is therefore a measure of how hard your marrow is producing right now, and in anaemia that is exactly the question: is the marrow making too little, or is blood being lost.
What is a normal reticulocyte count?
About 30 to 100 ×10⁹/L where the labs overlap; the national table uses 25 to 120. More important than the band is the combination with your haemoglobin. A count within the band with a low haemoglobin is already a marrow doing too little, because a healthy marrow responds to anaemia with more reticulocytes.
What does a low reticulocyte count mean?
With a normal haemoglobin nothing: the marrow is at rest. With a low haemoglobin that the marrow cannot work harder, usually because it lacks raw materials: iron most often, then vitamin B12 or folate. A chronic inflammation, a kidney disease and medicines that suppress the marrow do that too, and rarely a bone marrow disease. The next step is then ferritin, B12 and folate.
What does a high reticulocyte count mean?
That the marrow is working hard. With a low or falling haemoglobin blood is being lost, usually from the gut or through heavy periods, or red cells are being broken down, and then LDH and bilirubin rise with it. With a recovering haemoglobin it is good news: the marrow is topping up after a bleed or after starting iron or B12. With a normal haemoglobin it belongs to altitude, heavy endurance sport or a pregnancy.
Why do reticulocytes rise so quickly after iron or B12?
Because in a deficiency the marrow is ready to produce and only lacks the raw material. As soon as it is there, young cells are added within days, and after about a week you see that in the reticulocyte count, long before the haemoglobin moves. A rise is the sign that the deficiency was the cause and that the treatment is working. If it fails to come, something does not add up: the dose, the uptake, or the diagnosis.
What do reticulocytes have to do with sport and altitude?
At altitude the air is thinner and your body sets the marrow to making more red cells; reticulocytes rise within days and that is exactly the effect altitude training aims for. Anyone who runs a lot breaks down some red cells with the impact of every footstrike and keeps up with a slightly raised count. Both are normal. In doping control the reticulocyte count is, for that reason, one of the fixed values in the blood passport.
Why is there a per mille on my report?
Because reticulocytes are reported in two ways: as a count per litre and as a share of all red blood cells, in per mille. The share is misleading in anaemia, because with fewer red cells the same number of young cells looks like a larger part. The count per litre is therefore the more useful measure, and the band on this page applies only to that.
Do I need to fast for a reticulocyte test?
No. The count does not move with food. It does move with altitude and with heavy exertion in the days before, so mention that at the draw. It comes from the same tube as your blood count, so haemoglobin and MCV sit beside it automatically.
Which tests include reticulocytes?
Reticulocytes is part of Advanced, the broader panel. It is not orderable yet.
Related biomarkers
Sources
- 1.Unilabs, test catalogue (Dutch): reticulocytes. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): reticulocytes. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): reticulocytes. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): reticulocytes. 2026. clinicaldiagnostics.nl
- 5.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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Reticulocytes is part of Advanced, the broader panel. It is not orderable yet.
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