If your cat's Cryptococcus titers came from different laboratories or assay methods, a lower number does not by itself show that treatment worked. First confirm that each report measures Cryptococcus antigen, then check the method and specimen with your veterinarian. The ABCD feline cryptococcosis guideline identifies serum antigen detection as the first-line blood test. Cryptococcus antibody testing cannot distinguish subclinical infection from active disease and is not a substitute.

The practical rule is to keep serial serum titers at the same laboratory using the same method whenever possible. A published single-cat case report shows why: one serum sample was EIA-negative but latex-positive at 1:512; later paired latex results differed between laboratories. Those findings establish that disagreement can occur, not a conversion formula or a frequency of error. Treatment response still depends on the cat's examination and the pattern across comparable results.

Check the Cryptococcus line within a fungal panel

An antigen assay looks for a component of the fungus: its shed capsular polysaccharide. An antibody assay looks for the patient's immune response. These answer different questions. For feline cryptococcosis, ABCD recommends antigen detection; an antibody result cannot establish active disease. If a report only says 'fungal serology,' the panel heading alone does not tell you which kind of test was performed.

A useful example is Cornell AHDC's Feline Diagnostic Plans and Panels. Its fungal serology panel lists Aspergillus, Blastomyces, Coccidioides and Histoplasma antibody tests alongside Cryptococcus antigen, test code CRYPTA. It requests at least 1 mL of separated serum for that panel and notes that CSF is valid only for the Cryptococcus antigen test within the panel. These are Cornell's ordering details, not universal specimen requirements.

The same Cornell page includes Cryptococcus antigen in its neurologic diagnostic plan, accepting separated serum and appropriately collected cerebrospinal fluid (CSF). That does not make a CSF collection routine or necessary for every cat. It also does not identify the kit used for every CRYPTA submission. The clinic should confirm the current assay and accepted sample with the receiving laboratory.

Ask the clinic to clarify an abbreviated or imported report before deciding that the wrong test was ordered. A generic panel title may simply conceal a correctly performed antigen assay. What matters is the organism-specific result and its method. Bring the complete laboratory report, including comments, rather than relying on a phone summary such as 'the fungal test was positive.'

Identify the assay before comparing the numbers

The main formats discussed in the clinical literature are latex agglutination, lateral flow assays (LFA) and enzyme immunoassays (EIA). All can detect antigen, but their outputs are not interchangeable. A positive/negative screen, a strip intensity category and a dilution titer should not occupy one undifferentiated trend line.

What a latex titer means

In latex agglutination, antibody-coated particles react with antigen in a diluted sample. The endpoint titer describes how far the sample can be diluted while the reaction remains detectable. Thus 1:512 represents detection at a greater dilution than 1:32. It is not an antibody concentration, a fungal count, or a direct measure of the percentage of infection remaining. The report's own interpretation and method still matter.

ABCD describes a latex titer of 1:2 as positive. Heat and proteinase pretreatment can reduce interference and improve performance. McEwan and Sykes discuss how kit preparation and subjective reading can affect results. Their review cites latex sensitivity of 95–98% and specificity of 100% in earlier dog-and-cat studies; those estimates do not guarantee perfect performance in an individual cat or every laboratory.

What rapid lateral flow tests can establish

Lateral flow assays can provide results within minutes and are useful veterinary screening tools. In Krockenberger and colleagues' comparison, 129 feline serum specimens formed part of a larger multispecies study. Against latex testing, feline sensitivity was 92%, specificity 81%, positive predictive value 76% and negative predictive value 94%. The authors favored a screening role and recommended latex confirmation of positive LFA results.

In the separate 2019 US dog-and-cat study, CrAg LFA sensitivity and specificity were 92.0% and 93.2%; CryptoPS estimates were 80.0% and 94.9%. These were combined-species estimates against CALAS, with only 25 CALAS-positive specimens available and fewer tested on CryptoPS. They are not feline-only guarantees. Both study design and the reference test affect what these numbers establish.

Positive and negative predictive values also depend on how likely disease is in the tested population. A 94% negative predictive value in one study does not mean a negative strip excludes cryptococcosis with 94% certainty in every cat. Persistent compatible lesions or signs still need investigation. Conversely, screening many low-risk cats can produce misleading positives. The veterinary team combines the result with clinical suspicion and confirmation, rather than treating speed as proof of certainty.

What a negative EIA leaves unresolved

An EIA uses an enzyme-based signal to detect antigen and may support automated screening. It does not make a qualitative result equivalent to a latex dilution titer. ABCD discusses lower sensitivity of a commercial EIA in a human comparison; that is not a measured feline sensitivity estimate. The feline evidence here is the discordant single-cat report, not a population study proving that every EIA performs worse.

In that cat, five EIA results were negative over about seven months, and an EIA-negative sample subsequently tested positive by latex. The authors explicitly state that they could not retrospectively determine whether all earlier EIA negatives were true false negatives because contemporaneous confirmation had not been performed. A negative EIA that conflicts with the clinical picture therefore calls for veterinary review, not an assumption that treatment is complete.

What one cat's conflicting results actually show

The chronology in McEwan and Sykes' Table 1 is essential. It reports a treated cat with confirmed nasopharyngeal cryptococcosis. The selected observations below identify the assays compared on each date. The April 17 result of 1:512 predates the CALAS result of 1:32; the paired latex comparison on April 29 was 1:256 versus 1:32.

The simple ratio between 256 and 32 is eight. That describes those reported dilution endpoints only; it does not mean one laboratory always reads eight times higher. Another date in the same table produced a different ratio. The observation is especially useful when a referral or change of clinic changes where samples are sent: an apparent step in the chart may include a method effect as well as any biological change.

Read the trend alongside the examination

Once laboratory, method and specimen are consistent, serial antigen titers can help track response. Two feline cohorts illustrate that role. They do not set a deadline by which every cat's titer must fall or establish an exact dilution change that independently proves cure.

In Jacobs and colleagues' 1997 study of 35 cats, successful treatment was associated with a significant titer decline: about 1.3 orders of magnitude by two months and at least two orders by ten months. Nine of 16 successfully treated cats had undetectable titers by that later point. In five of six treatment failures, titers were unchanged or higher after at least six months. This was an older itraconazole-treated cohort using CALAS, so its trajectory is context rather than a required modern response curve.

A 2025 single-center Thai retrospective study analyzed serial response in 35 of 230 cats. CALAS titers and a six-domain clinical score improved over 12 months during an amphotericin B plus fluconazole regimen followed by fluconazole maintenance. The longitudinal analysis used baseline and approximately months 1, 3, 6, 9 and 12, rather than a standardized monthly schedule for every cat. Non-standardized visits, missing follow-up, selection and survivorship bias limit generalization.

Together these studies support following antigen results alongside clinical improvement. They do not justify comparing treatment success between laboratories or changing medication because one cat did not match the study average. The 1997 study did not find pretreatment titer magnitude to predict outcome. A high initial number is therefore not, by itself, a prognosis.

Falling titers can be reassuring when the examination is improving, while a sustained plateau or rise can prompt the clinician to reassess response. Antigen is not a direct viability test: low residual positivity can persist, and titers may continue falling after treatment has ended. A clinically improved cat with a low positive is a different question from an undiagnosed cat whose first test is weakly positive. Neither situation should be reduced to a single cutoff.

Keep the specimen consistent; serum is usually first

Serum is the usual first-line specimen because blood sampling is less invasive than CSF collection. A CSF titer and a serum titer measure different samples and should not be treated as consecutive points in one serum trend. Antigen can also be detected in other fluids, but the receiving laboratory must validate and accept the specimen for the requested test.

Sample requirements are laboratory-specific. Cornell's fungal panel requests at least 1 mL of serum; MiraVista's clinical review describes 0.25 mL of serum or CSF for its individual latex assay. These describe submitted laboratory sample volumes, not blood-draw instructions for owners. The clinic arranges collection, processing and submission and checks current requirements before the visit.

Resolve a result that conflicts with the clinical picture

Several different problems can produce a misleading result. They require different follow-up, so the useful question is why the result conflicts with the cat's signs, prior testing or examination—not which single number looks most reassuring.

• Very high antigen: excess antigen can interfere with detection, sometimes called postzone or a hook effect. ABCD notes that laboratory dilution can reveal positivity in affected samples. In the 2019 US study, a negative CrAg LFA at a CALAS titer of 1:4096 was considered possibly related to this effect; other higher-titer samples were LFA-positive, so the mechanism was not proven. Dilution is a laboratory investigation, not a home-testing step.

• Localized disease: serum can be negative with limited nasal or ocular infection. If compatible lesions persist, the veterinarian may pursue lesion cytology, histopathology, culture or other appropriate testing. ABCD cautions that a positive nasal-discharge culture alone may reflect carriage; the sampling site and evidence of tissue invasion matter.

• Low initial latex positivity: even 1:2 can be significant. MiraVista recommends confirming the diagnosis by other means if possible when the initial titer is at or below 1:200. That is a diagnostic caution from named clinical guidance, not a universal boundary between harmless and dangerous infection or an instruction to repeat a biopsy at every low monitoring result.

• Positive rapid screening: the LFA studies support confirmation, particularly where prevalence is low. The US study reported discordant positives in dogs with coccidioidomycosis. That canine observation demonstrates a possible limitation in the studied assays; it does not establish a feline cross-reaction rate. Your cat's clinician chooses confirmation appropriate to the assay and presentation.

Cats with respiratory signs can also need assessment for other causes. Our guide to cat sneezing and respiratory warning signs addresses that broader symptom question. A Cryptococcus report answers a narrower testing question; it does not explain every episode of sneezing or replace an examination.

Agree on a monitoring plan before the next sample

The following schedule comes from named clinical and laboratory guidance. The veterinarian adapts it to the individual cat. MiraVista is a commercial reference laboratory that offers cryptococcal antigen testing. Its clinical guidance recommends serum titers every two to three months during treatment, then at three months and every six to twelve months after treatment stops. Those intervals concern antigen surveillance; examinations and medication-safety monitoring may need a different schedule.

ABCD generally recommends continuing treatment until latex antigen is negative. McEwan and Sykes describe an ideal of two negative results one to three months apart. Clinical guidance also recognizes selected clinically recovered cats with low residual positivity. These require an individualized clinical judgment. A percentage or fold decline alone is not enough to decide that medication can end.

If serum antigen was negative even when the diagnosis was confirmed by another method, a persistently negative serum result cannot provide the same response marker as a declining positive titer. Ask what examination findings, lesion assessment or other evidence will guide that cat's follow-up. Similarly, apparent serologic resolution does not guarantee that relapse or reinfection is impossible.

Bring a complete record to the recheck

Bring every original report, especially after a referral. A useful record keeps collection date, laboratory name, method or kit if supplied, specimen, exact result and the laboratory's comments together. If a field is missing, ask the clinic to clarify it with the laboratory. Do not relabel a negative screen as a zero titer or silently merge results obtained with different methods.

• Is the Cryptococcus result an antigen assay, and what does this laboratory call the method?

• Are these serum results comparable with the previous samples, or did the laboratory or kit change?

• Does an initial low positive, a positive rapid screen or an unexpected negative need confirmation?

• How does the pattern fit the examination and the cat's response to medication?

• When are the next examination, antigen recheck and medication-safety checks due?

Tell the team about persistent or returning signs and any difficulty giving medication. Do not change doses, skip treatment or stop an antifungal because of one laboratory number. The purpose of keeping comparable reports is to give the veterinarian better evidence for the next decision.

Sources

1. Cornell University College of Veterinary Medicine, Animal Health Diagnostic Center. Feline Diagnostic Plans and Panels (Animal Health Diagnostic Center). Accessed October 29, 2026.

2. European Advisory Board on Cat Diseases (ABCD). ABCD Guideline for Cryptococcosis in Cats (updated November 2024; reviewed March 2026). Accessed October 29, 2026.

3. McEwan SA, Sykes JE. Nasopharyngeal cryptococcosis in a cat: interlaboratory variation in cryptococcal antigen assay test results (JFMS Open Reports, 2022). Journal of Feline Medicine and Surgery Open Reports. 2022;8(1):20551169221074624.

4. Krockenberger MB, Marschner C, Martin P, et al. Comparing immunochromatography with latex antigen agglutination testing for the diagnosis of cryptococcosis in cats, dogs and koalas (Medical Mycology, 2020). Medical Mycology. 2020;58(1):39-46.

5. Reagan KL, McHardy I, Thompson GR III, Sykes JE. Evaluation of the clinical performance of 2 point-of-care cryptococcal antigen tests in dogs and cats (JVIM, 2019). Journal of Veterinary Internal Medicine. 2019;33(5):2082-2089.

6. Jacobs GJ, Medleau L, Calvert C, Brown J. Cryptococcal infection in cats: factors influencing treatment outcome, and results of sequential serum antigen titers in 35 cats (JVIM, 1997). Journal of Veterinary Internal Medicine. 1997;11(1):1-4.

7. Veterinary Sciences (MDPI). Clinicopathological Features, Treatment Outcome, and the Cryptococcal Antigen Latex Agglutination System Titer in Feline Cryptococcosis Treated with Amphotericin B and Fluconazole (Veterinary Sciences, 2025). Veterinary Sciences. 2025;12(12):1211.

8. MiraVista Veterinary Diagnostics. Cryptococcosis in Cats and Dogs — Clinical Review and Test Guidance. Accessed October 29, 2026.