Serum amyloid A in cats with respiratory signs: two 2026 studies disagree

Researchers at AniCura Nordvet in La Madeleine reviewed records of cats seen in emergency for respiratory distress between October 2021 and December 2024. All 22 included cats had SAA measured within 48 hours of admission. Two internal medicine specialists who did not know the SAA results assigned each cat to a group.

There were 15 cats in the inflammatory group: aspiration pneumonia (7), feline lower airway disease (7) and pulmonary toxoplasmosis (1). The cardiac/neoplastic group had 7 cats: 3 with left-sided congestive heart failure (CHF) and 4 with neoplasia. Median SAA was 57.5 μg/mL in the inflammatory group and 5 μg/mL in the cardiac/neoplastic group. Because the assay could not measure below 5 μg/mL, any lower value was recorded as 5.

A cutoff of 8.6 μg/mL separated the groups best, with 80% sensitivity and 100% specificity. The authors described SAA as a possible supportive tool. Because of the small sample, they said the cutoff should not yet be used as a definitive rule-out threshold.

At Ludwig-Maximilians-University of Munich, researchers tested serum from 102 cats with respiratory signs and 20 healthy controls. The sick cats were grouped as feline lower airway disease, infectious lower airway or pleural space disease, neoplastic lower airway or pleural space disease, CHF, or upper airway disease.

Only one comparison between disease groups was significant. Cats with infectious disease had a higher median SAA (2.61 μg/mL) than cats with feline lower airway disease (0.14 μg/mL). Most of the high values in the infectious group came from cats with pyothorax, and most cats with other infections fell within the reference range. Every group's median was below the laboratory's reference limit of 6.7 μg/mL, and SAA did not differ significantly between sick and healthy cats.

The authors stressed that a normal SAA does not rule out infection and that the test should serve only as supporting information. Cats that died or were euthanized had higher SAA at admission than survivors, but the authors cautioned against using acute-phase proteins for prognosis. The French study found no survival difference.

The French team ran an in-house feline-specific immunofluorescence assay on fresh serum and noted that peer-reviewed validation data for that assay are lacking. The German team used an external lab's immunoturbidimetric assay. The French inflammatory group combined infectious and noninfectious cases. The German study separated them, and that is where its only significant difference appeared.

The patient groups and timing were also different. All the French cats were in respiratory distress, compared with 71 of the 102 German cats, and German cats in distress had higher SAA than those without distress. Five French cats were tested after receiving drugs. The German cats were sampled before treatment, and the authors noted that many were likely not sampled at the peak of the acute-phase response.

Median SAA was low in cats with CHF in both studies. A 2020 Journal of Veterinary Internal Medicine study, however, reported higher SAA in cats with CHF from primary cardiomyopathy than in cats with preclinical disease or in healthy controls. Both 2026 teams called for larger prospective studies.