Haemoplasma PCR (Mycoplasma haemofelis, M. haemocanis) in cats and dogs

What it shows

On a form this topic can appear in two lines:

• Mycoplasma haemofelis PCR (cats) — the main line. Cats have three main haemoplasmas: M. haemofelis, “Candidatus M. haemominutum” and “Candidatus M. turicensis”. M. haemofelis is the most pathogenic of them. Because PCR tells the species apart, a laboratory panel may list the other two in separate lines.
• Mycoplasma haemocanis PCR (dogs) — the dog species. “Candidatus M. haematoparvum” is also described in dogs.

PCR on EDTA blood is the method of choice. Looking for the organisms on a blood smear is unreliable: reported sensitivity ranges from 0% to 37.5%, and stain precipitate or other small specks on red cells can be mistaken for them. The organisms can disappear from the blood in as little as 2 hours.

Higher than reference — what it may be a sign of

For PCR, “higher than reference” means the DNA was detected. Possible explanations:

• Active infection — acute M. haemofelis infection can cause destruction of red blood cells (haemolytic anaemia), which in some cats becomes severe. In an anaemic cat a positive result points to a possible cause.
• Carrier without disease — carrier cats without anaemia exist, and the disease can rarely flare up again; chronic infection is usually not associated with significant anaemia. Detection alone does not confirm the disease.
• Other problems at the same time — FeLV and FIV infection are listed among risk factors, though not in every study. The two “Candidatus” species cause anaemia mainly in cats with a weakened immune system or other illness.

Quantitative PCR also measures how much haemoplasma DNA is in the sample.

Lower than reference

“Not detected” is the expected result. It does not exclude infection in every case. The number of M. haemofelis organisms in blood can fluctuate markedly over several months, and that “Ca. M. turicensis” has been found in tissues of cats whose blood PCR was negative. Once antibiotics are started, organism numbers can fall within a few days and the PCR can turn negative — this is why blood is taken before they are given. The vet decides whether to repeat the test.

Look at together with

• Haematocrit and haemoglobin — show whether there is anaemia and how deep it is.
• Reticulocytes — haemoplasma anaemia is typically regenerative, with large, pale red cells, but a marked rise in reticulocytes is not always seen and some cats have a non-regenerative anaemia.
• MCV and MCHC — large (macrocytic) and pale (hypochromic) red cells fit this picture.
• Coombs’ test — a test for antibodies stuck to the surface of red cells; it is often positive in cats with M. haemofelis.
• FeLV and FIV tests — vets may test for them as well.

Units and conversion

PCR has no units: the form shows “detected” or “not detected” for each haemoplasma species separately, so one panel may have two or three lines. A quantitative PCR may also give the amount of DNA in the sample. The app stores the result as text, as printed on the form.

Reference range

The reference range is on your lab’s form; for this PCR it is usually “not detected”. A positive result is read together with the haematocrit, reticulocytes and the cat’s condition: an infection with anaemia and a carrier without anaemia look the same on the PCR line. The result helps the vet choose the next steps.

Cats and dogs

Sources

1. ABCD (European Advisory Board on Cat Diseases) — Guideline for haemoplasmosis in cats
2. ABCD — Feline haemoplasma infections, fact sheet (April 2024)
3. Foley JE. Hemotropic Mycoplasma Infections in Animals. Merck Veterinary Manual, professional version
4. VCA Animal Hospitals — Feline Hemotrophic Mycoplasmosis
5. Cornell University Animal Health Diagnostic Center — Interpretation of PCR results