IMHA Testing: Blood Smear and Bloodwork in Cats

Name: IMHA Testing: Blood Smear and Bloodwork in Cats
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

If your veterinarian suspects IMHA in cats, bloodwork and a blood smear are the core tests used to confirm it. These tests show whether your cat's immune system is destroying its own red blood cells, and they help rule out other causes of anemia. This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

IMHA is diagnosed by combining a complete blood count, a blood smear review, and a saline agglutination test, with other tests used to rule out infections, cancer, and toxin exposure [1][2].
A blood smear lets your vet see red blood cell shape, clumping (autoagglutination), and other clues that point to immune destruction [3].
Anemia in IMHA can be regenerative (bone marrow making new cells) or non-regenerative, so a normal or low reticulocyte count does not rule it out [1].
Repeated bloodwork is expected. Your vet tracks hematocrit, reticulocytes, and platelet counts over days to weeks to judge whether treatment is working [3][2].
Costs vary widely by clinic and region, so ask your veterinarian for an itemized estimate before testing begins.

What Is IMHA Testing and Why Does Your Cat Need It?

Immune-mediated hemolytic anemia happens when the immune system mistakes red blood cells for threats and destroys them. Red blood cells carry oxygen, so when they are lost faster than the bone marrow can replace them, your cat becomes weak, pale, and short of breath [4]. IMHA is uncommon in cats and carries substantial mortality, which is why prompt testing matters [2].

The goal of testing is not just to find anemia. It is to prove the anemia is immune-mediated and to rule out everything else that can look similar. Many conditions cause anemia in cats, including infections, bone marrow disease, and blood loss. Your vet cannot treat IMHA confidently until those other causes are excluded [1].

Veterinarians use the 2019 ACVIM consensus criteria to diagnose IMHA in cats, which combine physical findings, bloodwork, and response to treatment [2]. Your vet may also screen for infectious diseases that can trigger immune-mediated red cell destruction, since IMHA can be non-associative (no clear trigger) or associative (linked to another disease) [1].

How Do Vets Confirm IMHA in Cats With Bloodwork?

Complete Blood Count

A complete blood count (CBC) measures red blood cells, white blood cells, and platelets. In cats with IMHA, the hematocrit (the percentage of blood made up of red cells) often drops well below normal. In one review of cats with IMHA linked to feline infectious peritonitis, the median hematocrit was 18%, with most cats falling between 13% and 20% [1].

The CBC also reports the reticulocyte count, which shows whether the bone marrow is responding by making new red cells. Regenerative anemia means new cells are being produced. Non-regenerative anemia means the marrow is not keeping up. In that same review, anemia was non-regenerative in 80% of cats and regenerative in only 11% [1]. This surprises many owners, because people often assume immune destruction always triggers a strong regenerative response. In cats, it often does not.

Platelets matter too. Concurrent thrombocytopenia (low platelets) was present in 40% of cats in that review [1]. Low platelets raise the risk of bleeding and can change how your vet manages treatment.

Blood Smear

The blood smear is where a lot of the diagnostic power lives. Your vet or a clinical pathologist examines a drop of blood under a microscope to look at cell shape, size, and behavior. In a published case of a cat with IMHA, the blood smear and blood examination showed regenerative anemia and autoagglutination, which supported the diagnosis [3].

Autoagglutination means red blood cells stick together in clumps, even when the sample is diluted. This happens because antibodies coat the cells and make them clump. Seeing true autoagglutination on a smear is one of the strongest clues that the immune system is involved. It also helps distinguish IMHA from rouleaux, a normal stacking pattern that can look similar to an untrained eye.

The smear can also reveal red cell fragments, spherocytes (rounded cells that have lost their normal shape), and other abnormalities. These findings guide your vet toward or away from IMHA.

Saline Agglutination Test

The agglutination test imha diagnosis relies on is simple and inexpensive. A drop of your cat's blood is mixed with saline and examined for clumping that persists after dilution. A positive saline agglutination test is one of the accepted criteria for diagnosing IMHA in cats [1].

In the FIP-associated IMHA review, cats were included if they had a positive saline agglutination test and/or a positive Coombs test, along with exclusion of other anemia causes [1]. The Coombs test (also called a direct antiglobulin test) detects antibodies or complement stuck to red blood cells. It is not available at every clinic, so the saline agglutination test is often the first-line option.

Other Bloodwork

Your vet will likely run a chemistry panel to check organ function, electrolytes, and proteins. This matters because IMHA treatment often involves immunosuppressive drugs, and your vet needs a baseline before starting them. If your cat is going on steroids, a pre-treatment blood test helps your vet choose a safe starting point and monitor for side effects. You can read more about that process in What to Expect When Your Cat Needs a Blood Test Before Starting Steroids.

If your cat is severely anemic and may need a transfusion, your vet will discuss crossmatching and compatibility. That process is explained in Blood Transfusion in Dogs and Cats: Crossmatching and Compatibility.

Your vet may also test for infectious diseases that can trigger or mimic IMHA. Choosing the right tests matters, and you can learn how vets approach that in Evidence-Based Test Selection for Infectious Diseases in Dogs and Cats.

How Do You Prepare Your Cat for IMHA Testing?

Most IMHA testing requires only a blood draw, so preparation is minimal. In many cases, no fasting is needed for a CBC or blood smear. If your vet is also running a chemistry panel, they may ask you to withhold food for a few hours. Follow your clinic's specific instructions.

Bring a list of all medications, supplements, and flea or tick products your cat takes. Some drugs can affect blood cells or immune function. Tell your vet about any recent illnesses, vaccinations, or possible toxin exposure.

If your cat is very weak, pale, or breathing fast, call ahead. Your vet may want you to come in immediately instead of waiting for a scheduled appointment. Severe anemia can become an emergency quickly.

What Happens During IMHA Testing?

Your cat will have blood drawn, usually from a leg vein or the jugular vein in the neck. The sample goes into tubes with different additives. One tube is used for the CBC and smear, another for chemistry, and sometimes a separate tube for coagulation testing.

The blood draw itself takes a few minutes. Most cats tolerate it well, though some need a mild sedative if they are stressed or struggling. Your vet will decide if sedation is safe based on your cat's condition.

Some tests run in-house and give results within an hour. Others are sent to an outside laboratory and take one to several days. The blood smear may be reviewed in-house or by a pathologist. If your cat is stable, you may go home and wait for results. If your cat is severely anemic, your vet may recommend hospitalization for monitoring and treatment while results come back.

Recovery Timeline and Home Care

IMHA treatment usually starts before every test result is back, especially if your cat is severely anemic. The table below shows a typical monitoring timeline. Your vet will adjust it based on your cat's response.

Timeframe	What to Expect
Day 0 (diagnosis)	Blood draw, smear, agglutination test, chemistry panel. Treatment often starts the same day.
Days 1 to 3	Repeat hematocrit and possibly reticulocyte count. Your vet watches for transfusion needs and treatment response.
Week 1	Recheck bloodwork. Hematocrit may rise slowly. Platelets and electrolytes are monitored.
Weeks 2 to 4	Ongoing rechecks. Immunosuppressive doses are often adjusted based on labs and side effects.
Months 1 to 3	Less frequent rechecks if values improve. Some cats relapse, so monitoring continues.
Long term	Periodic bloodwork. Two cats in one study achieved treatment-free remission lasting 4.2 and 1.9 years [2].

At home, give all medications exactly as prescribed. Do not stop steroids suddenly. Watch for increased thirst, urination, appetite changes, and behavior shifts, which are common steroid side effects. Keep your cat indoors and limit stress. Offer food and water frequently, and call your vet if your cat stops eating or seems weaker.

Possible Complications and Warning Signs

The most serious complication of IMHA is thromboembolism, where a blood clot blocks blood flow. This is rare in cats but has been reported. In one case, a 3-year-old cat with IMHA developed a clot in the main pulmonary artery, along with right-sided heart enlargement [3]. That cat improved with antithrombotic therapy, immunosuppressive therapy, and oxygen support [3].

Other complications include severe anemia requiring transfusion, low platelets with bleeding risk, and side effects from immunosuppressive drugs. Some cats relapse during or after treatment. In one study of 37 cats with non-associative IMHA, five cats relapsed, and four of those relapsed while still on immunosuppression [2].

Call your vet right away if you see:

Pale or white gums
Fast or labored breathing
Collapse or extreme weakness
Sudden inability to use the back legs
Vomiting, diarrhea, or refusal to eat
Bleeding from the nose, gums, or in the urine or stool

Questions to Ask Your Veterinarian

What tests are you running today, and what will each one tell us?
Is my cat's anemia regenerative or non-regenerative?
Did the blood smear show autoagglutination or other immune clues?
How often will we repeat bloodwork, and what values are we watching?
What is the estimated cost for the initial workup and follow-up rechecks?
What side effects should I watch for at home?
When should I bring my cat back, and what signs mean I should come sooner?

Limitations and When to Contact a Veterinarian

No single test confirms IMHA on its own. Diagnosis depends on putting together the CBC, smear, agglutination test, and exclusion of other diseases [1][2]. Some cats have negative agglutination tests but still have IMHA, and some have positive tests from other causes. Your veterinarian interprets results in the context of your cat's full history and exam.

Contact your vet the same day if your cat seems more tired than usual, eats less, or has a change in gum color. Go to an emergency clinic now if your cat is struggling to breathe, collapses, or has sudden weakness in the back legs. Schedule a routine recheck if your cat is stable but due for follow-up bloodwork.

Individual cases need a veterinarian who can examine your cat, review the full lab picture, and adjust treatment. Do not change medications or doses on your own.

Frequently Asked Questions

How accurate is a blood smear for diagnosing IMHA in cats?

A blood smear is very helpful but not perfect on its own. It can show autoagglutination and abnormal red cell shapes that strongly suggest immune destruction [3]. However, your vet still needs bloodwork and rule-outs to confirm the diagnosis [1][2].

Can IMHA in cats be diagnosed with bloodwork alone?

Bloodwork is the foundation, but most vets also use the blood smear and agglutination test. Ruling out infections, cancer, and other anemia causes is part of the process [1]. A single blood draw rarely gives a complete answer.

What does a positive agglutination test mean?

It means your cat's red blood cells clump together in saline, which points to antibodies attacking them. A positive saline agglutination test is one accepted criterion for IMHA in cats [1]. Your vet will combine it with other findings before making a diagnosis.

Why does my cat need repeated blood tests?

IMHA is a moving target. Hematocrit, reticulocytes, and platelets can change quickly, and treatment decisions depend on those trends [3][2]. Repeat testing also catches relapses and drug side effects early.

How much does IMHA testing cost in cats?

Costs vary by clinic, region, and how many tests are needed. There is no single standard price. Ask your veterinarian for an itemized estimate before testing so you know what to expect.

References

Immune-Mediated Hemolytic Anemia in Cats with Feline Infectious Peritonitis. Pathogens (Basel, Switzerland), 2025.
Clinical Findings, Treatment and Long-Term Outcome in 37 Cats with Non-Associative Immune-Mediated Hemolytic Anemia: A Retrospective Observational Study of Two Treatment Cohorts. Animals : an open access journal from MDPI, 2026.
Pulmonary thromboembolism due to immune-mediated hemolytic anemia in a cat: A serial study of hematology and echocardiographic findings. Frontiers in veterinary science, 2022.
Introduction to Blood Disorders of Cats - Cat Owners. Merck Veterinary Manual.