Reticulocytes
Reticulocytes are the red blood cells your bone marrow released in the last day or two. The count does not say how many red cells you have, but how hard your marrow is producing right now, and in anaemia that is exactly the question. Mind the unit: a count per litre and a per-mille are two different numbers.
Reticulocytes reference ranges
What does your value mean?
Normal: 30 to 100 ×10⁹/L
Enter your value as it appears on your results. Range for adults.
Reticulocytes high or low: what it means
Reticulocytes too low
A marrow that cannot work harder, because it lacks raw materials or is being held back.
| Cause | How often |
|---|---|
| Without 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 |
| Without B12 or folate the marrow cannot make DNA and the young cells get stuck; the red cells that do come are too large | Sometimes |
| An 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 |
| Chemotherapy and a few drugs for rheumatism or autoimmune disease suppress production; reticulocytes fall first | Sometimes |
| A marrow that does not work itself; rare, and usually the white cells and platelets fall with it | Rare |
Reticulocytes too high
A marrow working hard, because cells are being lost or because it is catching up on a deficiency.
| Cause | How often |
|---|---|
| From the gut, through heavy periods or after surgery; the marrow tops up and reticulocytes rise within days | Often |
| After starting iron, B12 or folate for a deficiency reticulocytes rise within a week; that is the sign the treatment is working | Sometimes |
| In 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 |
| Thin air sets the marrow to making more red cells; heavy endurance sport and a pregnancy also lift the count slightly | Sometimes |
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.
How does a reticulocytes blood test work?
- Fasting. Every draw is fasted: nothing to eat or drink from midnight, only water. Appointments are therefore in the morning, until 12:00.
- Referral. Not needed. You can have reticulocytes measured yourself, preferably together with a blood count and ferritin.
- 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
More about reticulocytes
Reticulocytes explained
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.
How do you read reticulocytes?
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. 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.
Frequently asked questions
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.
Related biomarkers
Sources 5
- 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
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