IMHA Toolkit
Clinical protocols & thrombosis prevention awareness
IMHA Relapse in Dogs
Relapse can occur while a dog is still receiving treatment, during medication tapering or after treatment has stopped. This evidence-based guide explains when recurrence can happen, which warning signs matter, how veterinary teams investigate a suspected relapse and how immunosuppressive treatment is subsequently managed.
⚡ Quick answer
An IMHA relapse occurs when immune-mediated destruction of red blood cells returns after a dog has previously responded to treatment. Published evidence suggests that relapse affects a minority of dogs that survive the initial episode, but recurrence may occur months or even years later.
What does an IMHA relapse mean?
In canine immune-mediated haemolytic anaemia (IMHA), the immune system destroys the dog's own red blood cells. Treatment aims to bring that immune-mediated destruction under control and allow the red cell count to recover.
A relapse means that evidence of immune-mediated red blood cell destruction returns after the disease had previously responded to treatment or entered remission.
Relapse is not the same thing as a dog simply appearing tired, panting more or experiencing medication side effects. Veterinary assessment and blood testing are needed to establish whether haemolysis has genuinely returned.
How common is IMHA relapse?
Reliable long-term relapse data are limited. One useful recent study from the Royal Veterinary College followed dogs with non-associative IMHA and examined when relapse occurred.
In the 2024 study, 68 dogs were included in the relapse-incidence analysis and nine experienced a relapse. Five of those nine relapses occurred within the first 12 months, two occurred between 12 and 24 months and two occurred later, at 35 and 48 months after the original diagnosis.
Six of the nine dogs that relapsed were still receiving immunosuppressive treatment at the time. Relapse therefore should not automatically be assumed to result from medication having been reduced too quickly.
When can an IMHA relapse happen?
Relapse can occur at several points in recovery:
- while a dog is still receiving immunosuppressive medication;
- during gradual reduction of prednisolone or another immunosuppressive drug;
- after immunosuppressive treatment has been discontinued;
- many months, and occasionally years, after the initial episode.
Remission therefore does not mean that IMHA can never return, although most dogs in the available long-term study did not experience a documented relapse.
What are the signs of an IMHA relapse?
The signs of relapse are usually related to renewed anaemia or haemolysis, but many are non-specific and can have other causes.
Possible return of anaemia or haemolysis
- Increasing lethargy or weakness
- Pale gums
- Yellow or jaundiced gums or eyes
- Dark, orange, red or brown urine
- Reduced appetite
- Rapid breathing or reduced exercise tolerance
- Collapse in severe cases
Common corticosteroid effects
- Increased thirst
- Increased urination
- Increased appetite
- Panting
- Restlessness
- Muscle loss
- Pot-bellied appearance
There can be overlap. Panting, for example, may occur as a corticosteroid side effect but may also accompany anaemia, pain or respiratory disease. Changes should therefore be interpreted alongside veterinary examination and blood results rather than used to diagnose relapse at home.
Sudden breathing difficulty, collapse, blue or grey gums, severe distress, acute neurological changes, severe abdominal pain or sudden loss of use of a limb can indicate a life-threatening complication, including thromboembolism. Seek urgent veterinary attention.
What should I do if I suspect a relapse?
Contact your veterinary practice promptly if your dog's energy, gum colour, urine colour, breathing or appetite changes significantly, particularly if your dog has a previous history of IMHA.
Do not independently increase, reduce, restart or stop prednisolone or another immunosuppressive medication. Symptoms that resemble relapse can also result from infection, gastrointestinal bleeding, medication toxicity or an unrelated illness.
How do vets confirm an IMHA relapse?
Veterinary assessment should establish whether the dog again has evidence compatible with IMHA rather than assuming that any new anaemia represents relapse.
Depending on the individual case, reassessment may include:
- PCV or haematocrit and a complete blood count;
- blood smear examination for evidence such as spherocytosis;
- assessment for agglutination;
- bilirubin and other indicators of haemolysis;
- reticulocyte response;
- evaluation for blood loss or another cause of anaemia;
- investigation for infection, inflammation, neoplasia or other possible triggers where indicated.
Consensus guidance recommends assessing for possible trigger factors that may disrupt immune homeostasis. Emerging infection deserves particular attention when relapse occurs while a dog is still receiving immunosuppressive treatment.
What happens to treatment after a relapse?
Treatment depends on how severe the relapse is, which medicines the dog is already receiving and when the relapse occurred.
The immediate goal is to re-establish control of the immune-mediated disease. Once remission has been achieved again, subsequent reduction of immunosuppressive medication may need to proceed more cautiously.
If relapse occurs during immunosuppressive tapering, ACVIM consensus guidance suggests increasing immunosuppressive treatment [Swann et al., 2019]. For a mild relapse this may mean returning to the dose used before the most recent reduction. A severe relapse may require reintroduction of the previously successful induction protocol.
Once remission is re-established, a slower subsequent taper may be appropriate. These recommendations are based substantially on clinical reasoning and expert consensus rather than high-quality comparative trials.
How is prednisolone normally tapered?
There is no single tapering schedule suitable for every dog. Tapering should be guided by the dog's clinical response and evidence that haemolysis remains controlled.
ACVIM consensus guidance
The 2019 ACVIM treatment consensus recommends considering the first reduction in prednisone or prednisolone when [Swann et al., 2019]:
- PCV or haematocrit has remained stable and above 30% for two weeks, and
- the majority of indicators of disease activity are improving.
The consensus recommends an initial reduction of approximately 25%. Provided stability continues, further reductions of approximately 25% may then be considered at intervals of around three weeks.
PCV or haematocrit should be reassessed before dose reductions and monitored during treatment. Other indicators of haemolysis may also be reviewed periodically.
These are consensus recommendations, not instructions for owners to alter medication themselves. Individual patients may require a different schedule because of disease severity, adverse drug effects, additional immunosuppressive medication or other medical conditions.
Does vaccination cause IMHA relapse?
This remains an area where evidence is limited.
In the 2024 RVC study, vaccination after diagnosis was not associated with relapse, and no dog in the study relapsed within 30 days of vaccination. However, the authors concluded that the role of vaccination in relapse remains unclear because the available evidence is not sufficient to establish the absence of risk in every circumstance.
Decisions about future vaccination should therefore be made individually with the dog's veterinary surgeon, taking into account previous disease, treatment status, infection risk and the importance of protection against preventable disease.
Can a dog relapse years later?
Yes. Although many relapses occur relatively early, late recurrence is possible. In the 2024 study, two of the nine dogs that relapsed did so more than two years after their original diagnosis — at 35 months and 48 months.
This does not mean owners need to monitor a recovered dog anxiously for life. It simply means that a previous history of IMHA remains clinically relevant and should be mentioned to any veterinary surgeon treating the dog in future.
Frequently asked questions
Can IMHA come back after my dog has stopped medication? ▼
Yes. Relapse can occur after treatment has finished, although published evidence suggests that it affects a minority of dogs that survive the initial episode. Late relapse has been documented more than two years after diagnosis.
Does a relapse mean my dog will not recover? ▼
Not necessarily. A relapse means that disease control has been lost and treatment needs reassessment. Some dogs can return to remission after treatment is adjusted. Prognosis depends on the severity of the relapse, complications and the individual dog's response.
Can steroid side effects look like an IMHA relapse? ▼
Yes. Panting, weakness, muscle loss, increased thirst and behavioural changes can occur during corticosteroid treatment. Because some symptoms overlap with illness, blood testing and veterinary assessment are important when a dog's condition changes.
Should I increase prednisolone if I think my dog is relapsing? ▼
No medication change should be made without veterinary instruction. A suspected relapse should first be assessed because other conditions can cause similar symptoms or anaemia.
When is relapse most likely? ▼
There is no single predictable relapse window. In one 2024 study the median time to relapse was six months and five of nine relapses occurred within the first year, but later relapses were also documented.
Continue learning about canine IMHA
Relapse is only one part of the recovery journey. These IMHA Toolkit resources explain what happens after diagnosis and which warning signs require urgent attention.
Supporting Studies
Review the original peer-reviewed source materials for detailed relapse and tapering analyses.
Sparrow AJ, Swann JW, Glanemann B. Long-term relapse timing and post-diagnosis vaccination associations in dogs with immune-mediated disease.
Open on Wiley Online Library →Consensus recommendations for immunosuppressive treatment, monitoring, tapering and management of relapse in canine IMHA.
View in the IMHA Toolkit Evidence Library →