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Reticulocyte Count (Percent)

The share of your red blood cells that are brand new. It shows how actively your bone marrow is making red cells.

AI-verified against cited sources. Awaiting expert reviewAlso called RET%, Retic %LOINC 17849-1

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What it is

Reticulocytes are young red blood cells that your bone marrow has just released. They spend about one to two days in the blood before they mature into regular red cells. This result shows them as a percentage of all your red blood cells. A lab can count them by machine, or by looking at a stained blood sample under a microscope. It is usually read together with your hemoglobin or hematocrit, because the same percentage can mean different things in a person with anemia and a person without it.

Why it matters

The reticulocyte percentage is a quick look at how hard your bone marrow is working. When red cells are lost or break down faster than usual, the marrow normally speeds up and the number goes up. When the marrow can't make enough red cells, the number can be low, or lower than expected for your level of anemia. Clinicians use it to help sort out the cause of anemia and to see whether treatment is working. On its own it doesn't point to a cause.

If it’s low

A lower-than-usual percentage means your bone marrow is releasing fewer new red cells than expected. If your hemoglobin is also low, that can point to a problem with making red cells rather than losing them. Your clinician reads it together with your hemoglobin, because the same percentage means different things depending on whether you have anemia.

Common causes

  • Low iron (iron deficiency anemia)
  • Low vitamin B12 or folate
  • Kidney disease
  • Scarring of the liver (cirrhosis)
  • Aplastic anemia or other bone marrow problems, including after chemotherapy or radiation
  • Some medicines

What can help

  • Ask your clinician whether iron, vitamin B12 and folate levels should be checked
  • Ask whether kidney or liver tests would help explain it
  • Eat a balanced diet that includes iron, B12 and folate foods, and keep up with routine checkups

If it’s high

A higher-than-usual percentage means your bone marrow is releasing new red cells faster than usual. That is a normal response when the body is making up for red cells it lost, for example after bleeding or when red cells break down early. It can also be a sign that treatment for anemia is working. Your clinician reads it together with your hemoglobin and other results.

Common causes

  • Recovery after treatment for low iron, vitamin B12 or folate (a sign the marrow is responding)
  • Pregnancy
  • A recent stay at high altitude
  • Some medicines
  • Recent or ongoing bleeding
  • Red cells breaking down faster than normal (hemolytic anemia)
  • Hemolytic disease of the newborn, in babies
  • A counting error from the analyzer, such as from blood parasites or fluorescent medicines

What can help

  • Ask your clinician whether your hemoglobin and other tests point to a cause
  • Ask whether a repeat test, or a corrected count that adjusts for your hematocrit, would help
  • Tell your clinician about recent bleeding, heavy periods, high-altitude travel or new medicines

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

See Retic % by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Anemia: the same percentage can mean different things depending on your hematocrit, so clinicians sometimes use a corrected count
  • Pregnancy and time at high altitude, which can raise the count
  • Age and sex: ranges differ in newborns and children, and some labs print different adult ranges for men and women
  • The counting method and analyzer: manual stain counts and automated counts can differ
  • Recent bleeding, a transfusion, or treatment for anemia
  • Some medicines
  • Malaria parasites, and some medicines that give off their own fluorescence, can make automated counts read falsely high. Fragments of red cells can make them read falsely low. Labs look at a blood film when the analyzer raises a flag.
  • Certain inclusions inside red cells, such as Heinz bodies or the Hb H inclusions of Hb H disease (a form of alpha thalassemia), can throw off automated counts.
  • Pregnancy, a recent move to high altitude, and some medicines can raise the count.
  • Recent blood loss, a blood transfusion, or treatment for anemia (such as iron, vitamin B12, folate or erythropoietin) can change the count within days.
  • Blood is drawn into an EDTA tube and tested within a time limit that each lab sets. Mayo Clinic Laboratories accepts a reticulocyte sample for up to 24 hours at room temperature or 48 hours refrigerated.

Changes within days, because reticulocytes spend only about 1 to 2 days in the blood before they mature.

When to talk to a clinician

Labs don't usually publish an urgent-call limit for this result. Contact a clinician if a high or low result comes with tiredness, shortness of breath, dizziness, a fast heartbeat, pale skin, or yellowing of the skin or eyes. Call 911 or your local emergency number for chest pain, severe shortness of breath, fainting or confusion.

Questions you could ask

  • How does my reticulocyte count fit with my hemoglobin?
  • Does this result need a correction for my hematocrit?
  • Could recent bleeding or red cells breaking down faster explain this?
  • Is this a sign that my treatment is working?
  • Should we repeat it or add tests such as a corrected count or bilirubin?
  • Could low iron, B12 or folate explain this?

Questions people ask

What is the difference between the reticulocyte percent and the absolute count?

The percent is the share of your red blood cells that are reticulocytes. The absolute count is the number of reticulocytes in a set amount of blood. If you have anemia, the percent can look high only because you have fewer red cells in total. The absolute count, or a corrected count that adjusts for your hematocrit, avoids that problem. Many labs print both.

Does a high reticulocyte count mean something is wrong?

Not necessarily. A high count means your bone marrow is releasing more new red cells than usual. That can be a healthy response to blood loss, or a sign that treatment for low iron, B12 or folate is working. Pregnancy and a stay at high altitude can also raise it. It can also happen when red cells break down early. Your clinician looks at it together with your hemoglobin and other results.

Why does my lab's range differ from the one I read online?

Labs count reticulocytes with different methods and analyzers, so their ranges differ. Mayo Clinic Laboratories lists 0.60 to 2.71% for adults, Labcorp's sample report shows 0.6 to 2.6%, and some hospital labs print upper limits closer to 1.8 to 2.2%. Use the range printed on your own report.

Show the science and sources

Units

  • 1 % = 1 %
  • 1 % = 10 ‰

Open the Retic % unit converter

For clinicians and researchers

Reticulocytes are anucleate immature red cells with residual RNA that circulate for about 1 to 2 days before maturing (StatPearls; MedlinePlus). They are counted by new methylene blue supravital staining or by flow cytometry with RNA-binding fluorescent dyes (Mayo and CRMC use flow cytometry; CLSI-ICSH H44 covers the methods). The percentage is relative to red cells, so it rises in anemia even when production is flat. The absolute count (percent × RBC) and the corrected count or reticulocyte production index adjust for this. One published RPI formula is (reticulocyte % ÷ maturation time) × (hematocrit ÷ 0.45), with a maturation time of 1 day for hematocrit 40% or higher, 1.5 days for 30–39.9%, 2 days for 20–29.9% and 2.5 days for under 20% (BMC Cardiovasc Disord 2026). Reference limits depend on the method and analyzer, and several labs publish sex-specific adult limits. In 5,692 Chinese adults measured on a Sysmex XN-B3, all reticulocyte indices except MFR differed significantly by sex, and most changed with age (BMC Cardiovasc Disord 2026). In a Sysmex XN 9000 evaluation of 510 samples, 8.6% showed interference: parasites such as malaria and autofluorescent drugs gave spuriously high counts and red cell fragments gave spuriously low counts, so a blood film check is advised when the analyzer flags a result (Clin Lab 2019). Heinz bodies and Hb H inclusions can also distort automated counts. The same analyzers report the immature reticulocyte fraction (IRF), reticulocyte hemoglobin (Ret-He or CHr) and reticulocyte volume, which add information about marrow output and iron supply (Clin Lab Med 2015).

LOINC 17849-1 (primary), 4679-7, 31112-6, 17848-3. Specimen: whole-blood.

Sources

  1. Reticulocyte Profile, Blood (test RETB), Mayo Clinic Laboratories (catalog mirror at testcatalog.org)
  2. Reticulocyte Count (test 005280), sample report, Labcorp (2016)
  3. Reticulocyte Count (test code Reticulocyte), CRMC Laboratory Test Catalog
  4. Sysmex Complete Blood Count Reference Ranges (March 2024), Vanderbilt Medical Laboratories (2024)
  5. Hematology Reference Intervals (updated April 2026), HNL Lab Medicine (2026)
  6. Derivation of Russian-specific reference intervals for complete blood count, iron markers and related vitamins, PLoS One (2024)
  7. Reticulocyte Count, MedlinePlus (NIH National Library of Medicine)
  8. Histology, Reticulocytes, StatPearls (2023)
  9. Clinical utility of reticulocyte parameters, Clinics in Laboratory Medicine (2015)
  10. Reticulocytes: reference limits, Clinical and Laboratory Haematology (1996)
  11. Age- and sex-specific normative values for reticulocyte indices and their relation to early-stage CKM syndrome, BMC Cardiovascular Disorders (2026)
  12. Interferents of Automated Reticulocyte Analysis Integrated with Relevant Clinical Cases, Clinical Laboratory (2019)
  13. Heinz bodies interfere with automated reticulocyte counts, Haematologica (1999)
  14. Interference of Hb-H disease in automated reticulocyte counting, Clinical and Laboratory Haematology (1999)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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