Cats: A Different Biology, a Different Testing Strategy
Quick Answer — Feline testing differs from canine testing in three ways that matter clinically: the acute-phase response is carried by SAA rather than CRP, retrovirus screening has specific rules about age and confirmation, and the thyroid–kidney interaction means two systems must be read together. A feline protocol built by adapting a canine one will be wrong in all three places.
Quick Answer
Same menu, different interpretation. The species determines which marker, which window, and which confounder.
Three species-specific differences
1. Acute-phase response. SAA is the dominant feline acute-phase protein; CRP rises modestly. Using CRP as the feline inflammation marker understates the response — and cats are the species where the clinician is most often working with thin examination findings.
2. Retrovirus rules. FeLV antigen and FIV antibody are the screening tests. Both have specific rules:
| Situation | Rule |
|---|---|
| Cat of unknown status | Screen once; retest if exposure risk continues |
| Kitten under ~6 months | Retest after the maternal antibody window before declaring positive |
| Low-risk cat, positive result | Confirm before a lifelong diagnosis is communicated |
| Vaccinated against FIV (where applicable) | Antibody cannot distinguish vaccination from infection |
3. Thyroid and kidney. Hyperthyroidism raises filtration and can mask reduced renal function. Treating the thyroid can unmask azotaemia, so T4 and renal parameters are measured together, before and after treatment — a rule that exists only in cats.
The feline testing matrix
| Clinical picture | First-line tests |
|---|---|
| Acute upper respiratory signs | FCV and FHV antigen from oropharyngeal/conjunctival swabs |
| Effusion, fever of unknown origin, young cat | FCoV on effusion, with effusion protein and A:G ratio — not serum antibody |
| Vomiting, weight loss, jaundice | fPL plus SAA; assess liver and gut as well |
| Weight loss, polyphagia, palpable thyroid | T4 with renal parameters |
| Anorexia, non-specific illness | SAA, with renal and thyroid assessment |
| Chronic weight loss, anaemia, recurrent infection | FeLV antigen + FIV antibody together |
What feline testing punishes
- Assuming dogs’ markers transfer. CRP is a weak feline signal.
- Diagnosing FIP from an antibody titre. Exposure is near-universal in multi-cat environments; disease is rare.
- Declaring a kitten FIV-positive. Maternal antibody is expected.
- Treating hyperthyroidism without checking renal function. Azotaemia gets unmasked.
- Excluding hyperthyroidism on one normal T4. Early disease sits inside the interval.
Handling and stress
Cats tolerate handling poorly, and sample quality suffers: small volumes, difficult venepuncture, delayed separation. For analytes sensitive to handling, the practical answer is to control the pre-analytical chain — minimise handling, separate promptly, and record the delay.
Where the menu ends
Data pending. This section reports measured values from internal validation studies. They are published once the supporting study is complete; the current report is available from technical support on request.
Six traps
- Canine markers in cats. Understates inflammation.
- Antibody for FIP diagnosis. The most consequential feline interpretation error.
- One normal T4 as a rule-out. Repeat testing is the standard.
- Unconfirmed retrovirus positives. Confirm before lifelong advice.
- Ignoring renal function when treating thyroid disease. Classic oversight.
- Poor sample handling in a difficult venepuncture. The result reflects the sample, not the cat.
The Author’s Take
Position. Feline content should be written by someone who works with cats, because the failure modes here are feline-specific and a canine page with “cat” substituted in will actively mislead.
Reasoning. The three differences above are not trivia — each one changes a diagnosis. A vendor that publishes a genuinely feline protocol, with SAA as the inflammatory marker, retrovirus rules that protect kittens from a life sentence, and the thyroid–renal interaction stated up front, is demonstrating something a menu cannot: that the company understands the species it claims to serve. In feline practice, that demonstration is the entire basis of trust, because cats do not forgive a wrong call.
Disclosure. Clinical guidance, not a performance claim. Figures marked indicate where platform data must be inserted.
Related pages
- Kittens · Seniors · Dogs
- Feline infectious disease index · Feline pancreatitis · Renal · Endocrine
- Feline SAA
Sources
- Reference to be added.
- Reference to be added.
- CLSI EP28-A3c — feline reference intervals.
Frequently asked questions
- Why is SAA preferred over CRP in cats?
- Because the feline acute-phase response is carried mainly by serum amyloid A. CRP rises modestly in cats compared with dogs, so a canine-marker strategy applied to a cat can understate an inflammatory response that is clinically significant.
- Should every cat be tested for FeLV and FIV?
- All cats of unknown status should be screened at least once, and any cat with exposure risk should be retested. Positive results need confirmation, and kittens under about six months should be retested after the maternal antibody window rather than being declared positive.
- Why do thyroid and kidney results have to be read together?
- Hyperthyroidism increases glomerular filtration and can mask reduced renal function. Treating the thyroid disease may unmask azotaemia, so both parameters belong in the same monitoring plan, before and after treatment.