The finding is always interpreted alongside the red blood cell count, haemoglobin and haematocrit. Haematocrit shows the proportion of blood made up of red blood cells. A high reticulocyte count alone does not show how severe the anaemia is or whether red blood cell loss has stopped. Reticulocytosis can also occur without concurrent anaemia.
When to see a vet urgently
Seek emergency care if your cat has any of these signs:
- very pale or almost white gums and severe weakness;
- difficulty breathing or open-mouth breathing;
- collapse or inability to stand normally;
- heavy bleeding, a serious injury or rapid deterioration;
- jaundice or dark urine together with clear signs of illness.
Do not wait for another blood test if your cat's condition worsens. You can find a vet near you.
Overview
Reticulocytes are immature red blood cells that still contain remnants of RNA, identifiable with special stains. An increase shows that the bone marrow is actively producing new red blood cells to replace mature cells that have been lost. In anaemia, the reticulocyte count helps distinguish regenerative from non-regenerative disease.
In cats, aggregate and punctate reticulocytes are distinguished. In aggregate forms, RNA appears in larger clumps. As the cell matures, it becomes a punctate reticulocyte, containing only small dots of RNA. These are maturation stages of the same cell, rather than two separate red blood cell lineages.
Aggregate reticulocytes in particular are counted when assessing the current bone marrow response. Punctate forms remain in circulation longer, so their presence may reflect earlier rather than ongoing new cell production. A cat's result therefore cannot be interpreted directly using the approach applied to canine reticulocytes.
Causes
- Sudden blood loss from injuries, internal bleeding or surgery.
- Haemolytic anaemia caused by infection, such as Mycoplasma haemofelis, immune-mediated disease or poisoning.
- Iron deficiency, which is less common than in people.
- Recovery after treatment for anaemia, indicating a treatment response.
- Tissue oxygen shortage, prompting the body to increase red blood cell production.
Iron deficiency needs clarification: prolonged blood loss may initially increase new cell production, but the response can weaken as iron stores run out. Not every iron-deficient cat therefore has reticulocytosis. Iron deficiency in cats is often caused by ongoing blood loss, rather than simply low dietary iron.
Haemolysis means premature destruction of red blood cells. Its cause cannot be identified from the reticulocyte count. Immune-mediated disease, a substance that damages red blood cells and haemoplasma infection need different investigations and treatment. Increased red blood cell production associated with impaired oxygen transport is also possible when the cat is not anaemic at the time of examination.
Risk factors
- cats living outdoors, with risks of injury, blood loss and parasites;
- cats with chronic infection, such as FeLV or FIV;
- kittens and young cats that readily acquire parasites;
- cats after surgery or heavy bleeding.
This list does not mean that these cats always have reticulocytosis. Information about the exact level of risk is limited, and underlying disease may also impair red blood cell production. FeLV infection, for example, can involve bone marrow dysfunction and non-regenerative anaemia. A positive viral test alone does not explain the reticulocyte finding.
Typical symptoms
Reticulocytosis itself causes no symptoms. All symptoms arise from the underlying disease or anaemia:
- pale mucous membranes;
- weakness and listlessness;
- faster breathing and heart rate;
- weight loss;
- signs of bleeding or haemolysis, such as dark urine, jaundice and visible bruising.
The severity of symptoms depends on both the severity of anaemia and how quickly it develops. A cat becoming anaemic slowly may adapt and initially seem only more tired than usual. Sudden blood loss can quickly cause a serious situation. The absence of visible bleeding does not rule out internal bleeding.
Digestive tract bleeding can cause very dark, tar-like faeces. Jaundice may be associated with red blood cell breakdown, but can also have another cause. Tell the vet about these observations. The reticulocyte count cannot be determined from mucous membrane or urine colour alone.
Complications and consequences
- reticulocytosis is a compensatory response, but may be inadequate with heavy blood loss;
- it may indicate progression of the underlying disease;
- if the finding persists, a chronic source of blood loss or haemolysis needs investigation.
However, a persistent finding alone does not prove that disease is worsening. Interpretation requires knowing which reticulocyte form was counted and how the haematocrit and the cat's condition are changing. If red blood cells are lost faster than the bone marrow can replace them, anaemia may continue despite a good production response. Increased production therefore does not guarantee adequate oxygen transport.
Diagnosis at the vet
- a complete blood count and reticulocyte measurement, including absolute count and percentage;
- a blood smear to assess red blood cell shape and blood parasites;
- blood biochemistry to assess the liver, kidneys and electrolytes;
- FeLV and FIV tests;
- ultrasound and X-rays to look for internal bleeding.
Why is the absolute count useful?
The percentage shows the proportion of all red blood cells that are reticulocytes. When mature red blood cell numbers fall, the percentage may look high without enough new cells being produced for the severity of the anaemia. The absolute count gives the number of reticulocytes in a particular volume of blood. The vet compares it with the degree of anaemia and the laboratory's reference values.
A blood smear complements machine analysis. Young red blood cells may be larger than usual and stain differently, but a high mean cell volume alone does not demonstrate effective regeneration. Finding nucleated red blood cells is not the same as a reticulocyte response either: they may occur with other bone marrow or circulatory disorders.
When should the sample be repeated?
The bone marrow needs time to respond to sudden anaemia. A very early sample may contain few reticulocytes even if clear regeneration develops later. In that situation, the result does not yet establish a permanent production disorder. The timing of repeat sampling is chosen according to when the anaemia began, its suspected cause and the cat's condition.
Check-ups assess trends in the red blood cell count and haematocrit alongside reticulocytes. A fall in the reticulocyte count alone does not mean treatment has failed: the need to produce new cells may decrease as anaemia resolves. Conversely, a persistently low haematocrit and worsening condition require a new overall assessment.
How is the cause investigated?
The history covers injuries, surgery, diet, parasite status, all medicines and possible toxin exposure. If blood loss is suspected, visible and hidden bleeding sources are investigated. Clotting tests or digestive tract investigations may be needed if the history and findings suggest them. Imaging is selected according to the suspicion, rather than automatically for every cat.
When haemoplasmas are suspected, a blood PCR test is more sensitive than a smear. Where possible, the sample is taken before antimicrobial treatment, as treatment may reduce the number of detectable organisms. A positive result is considered alongside symptoms and other findings: symptom-free carriers also occur. Failure to see organisms on a blood smear does not alone rule out infection.
Treatment and follow-up
Reticulocytosis is not usually treated by lowering the count. The source of blood loss is stopped, an identified infection is treated or the condition destroying red blood cells is controlled. Immune-mediated disease may require medicines affecting the immune system, but these are not selected on the basis of reticulocytosis alone. Not all haemolytic anaemias are the same.
A severely anaemic cat may need a blood transfusion while the cause is investigated and treated. Donor and recipient blood compatibility is tested to reduce harmful reactions. Transfused red blood cells support oxygen transport but do not remove ongoing bleeding or the cause of haemolysis. The response to treatment is monitored after transfusion too.
Do not start an iron supplement yourself because of a high or low reticulocyte count. If deficiency is confirmed, the cause of blood loss is investigated and treated at the same time. An ordinary complete, balanced diet does not replace treatment of a bleeding intestinal lesion or parasitic disease. Do not give human iron products or painkillers without veterinary instructions either.
At home, monitor appetite, energy, breathing and possible signs of bleeding. Tell the treating practice about new dark faeces, changes in urine colour, jaundice or deterioration. Planned blood checks are needed even if your cat seems brighter. Prognosis depends above all on the underlying disease and its response to treatment.
Prevention
- regular worming and flea control to prevent blood loss and blood parasites;
- vaccination and monitoring for viral infections, including FeLV and FIV;
- avoiding toxic substances and foods;
- monitoring after surgery and injuries;
- regular blood tests for older and chronically ill cats.
Parasite control is planned according to exposure risk and local conditions. It can prevent blood loss caused by blood-feeding parasites. However, the role of fleas in transmitting haemoplasmas is poorly established, so flea control should not be considered reliable protection against haemoplasmas. The need for FeLV vaccination and viral testing is assessed separately; vaccination does not prevent every cause of anaemia.
Important for cat owners
Reticulocytosis is an important laboratory finding, rather than a disease in its own right. It shows that the body is actively responding to anaemia. Remember that if your cat is lethargic, has pale mucous membranes or shows signs of blood loss, you should take it to a vet promptly. A blood test and reticulocyte count help identify the source of the problem and select the right treatment.
This article provides general information and does not replace veterinary care. If you notice signs of illness in your cat, contact a vet.
Frequently asked questions
Is reticulocytosis the same as anaemia?
No. Anaemia means too few red blood cells or too little haemoglobin; reticulocytosis means increased young red blood cells. They often occur together, but the reticulocyte count can also be raised without concurrent anaemia. Both results are assessed as part of the whole blood test.
Does a high reticulocyte count mean my cat is recovering?
It shows a production response but does not alone confirm recovery. Blood loss or cell destruction may continue faster than production. Changes in the cat's condition and haematocrit show whether the anaemia is actually resolving.
Does a low reticulocyte count rule out blood loss?
No, if the anaemia began recently. The bone marrow response may not be visible in the first sample. The vet assesses whether repeat sampling is needed, but treatment of a seriously ill cat is not delayed while waiting for a response.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Reticulocyte %, eClinpath / Cornell University, accessed 2026-11-03.
- Regeneration, eClinpath / Cornell University, accessed 2026-11-03.
- Anaemia in Cats, Merck Veterinary Manual, accessed 2026-11-03.
- Anaemia, Cornell Feline Health Centre, accessed 2026-11-03.
- Guideline for Haemoplasmosis in Cats, ABCD, accessed 2026-11-03.
- Haematology and Immune-Related Disorders, The Cat / PubMed Central, accessed 2026-11-03.
- Guideline for Feline Leukaemia Virus Infection, ABCD, accessed 2026-11-03.