Determining Immune Status

  • 1. Introduction

  • 2. Complete Blood Count (CBC) with Differential

  • 3. CD4+ (T4) Lymphocyte Count

  • 4. Viral Load

  • 5. Clinical Health

  • 6. Some Testing Facilities

  • Click here to open a Glossary of Terms in a separate window.


  • 1. Introduction

  • The immunological benchmark for predicting disease advancement in the direction of AIDS has yet to be described. There is no Gold Standard for determining the immune status of FIV+ cats. At least four measurable elements are relevant to the determination: Complete Blood Count (CBC) with Differential, CD4+ (or T4) Cell Count, Viral Load, and Clinical Health. For reasons that vary in each case, each element, while adding important information, is unreliable at any given moment in offering a complete and accurate picture of immune status. Ideally, as many of these elements as possible can be looked at in order for the most complete and accurate picture to emerge. Several other immune parameters are relevant, but cannot be conveniently assessed. These include the functionality of key immune cells, the level of chronic immune activation and cell turnover, and the presence of various markers of systemic inflammation, all contributing to what has sometimes been described as “immune exhaustion.” (See the discussion of anergy further on.) Persisting elevation of globulin on serum chemistries and persisting reversal of normal neutrophil:lymphocyte ratios sometimes point to virally-induced hyperimmune activity.

  • 2. Complete Blood Count (CBC) with Differential.

  • CBC with differential contains a variety of information. The pertinent values are the white blood cell count (WBC) and the red blood cell count (RBC). The differential refers to the breakdown of the white cells into individual types. The Reference Range of normality differs from lab to lab, but not by large amounts. (Click here to view Reference Ranges in a separate window.)

  • Most asymptomatic and symptomatic FIV+ cats do not have significantly different WBCs from FIV- cats, although a small portion of even asymptomatic cats have been noted with cytopenias. Therefore, WBCs that hang at the lower end of the reference range or slightly below it for a series of CBCs over a period of time are cause for suspicion that disease progression has taken place. Low WBCs should always be regarded as abnormal. Numerous conditions can cause low WBCs, but in the absence of such conditions, low and low normal counts are characteristic of cats that have advanced beyond the “being FIV+ has hardly made a difference” stage. WBCs well below normal are characteristic of cats either at the AIDS stage of their infection or in the process of entering it. WBCs below 3500 or so are considered low.

  • Disease progression may express itself with one or the other of the pertinent white cells in the differential. Again, most asymptomatic FIV+ cats do not show a significantly different differential from FIV- cats. Therefore, persisting low lymphocytes (“lymphopenia”) in the absolute and in relation to overall white counts (expressed as a percentage) is probably one manifestation of advanced FIV infection. In HIV medicine, a persisting count of fewer than 1250 lymphocytes is used to predict an AIDS-defining number of CD4+ lymphocytes in places where CD4+-testing is unavailable. Marcel Blanc, whose cat Zouzou probably at the time was in the late-ARC stage of infection, showed a marked lymphopenia (around 900) at approximately the same time as he registered a viral load of 160,000 copies/ml, a substantial, but not necessarily AIDS-defining viral load.

  • Persisting low neutrophils (“neutropenia”) are also often a characteristic feature of FIV disease progression, despite the fact that neutrophils (unlike lymphocytes) are not primary targets of the virus. Neutropenia, a characteristic finding in initial acute FIV infection, is less common than lymphopenia as a stage marker of disease progression, according to some studies, more common according to others. Dianne Hayes’ cat Max experienced periodic fluctuations of neutrophil counts from low normal to low (eventually under 1000), indicating a late ARC stage infection possibly grading into AIDS.

  • For reasons that become clear subsequently, attention to the whole spectrum of means of interpretation of both CD4+ counts and viral loads may be necessary in order to get a clear picture of immune status.

  • Red blood cells, although they are not objects of FIV, can nevertheless mirror immune status. Asymptomatic FIV+ cats have statistically lower hematocrit (HCT) or packed cell volume (PCV) when compared to FIV- cats, but the numbers will still lie within the normal reference range and are highly variable in individual cats and situations. But a persisting low or low-normal hematocrit (HCT) or packed cell volume (PCV) is often characteristic of a symptomatic FIV+ cat. Of course, anemia is characteristic of many illnesses. However, a cat whose hematocrit drops below 25 or so without other discernable pathologies and whose anemia is nonregenerative is often showing disease advancement. (FIV+ cats with advanced infection may be peculiarly liable to the blood parasite hemobartonella felis/Mycoplasma haemofelis, which can cause regenerative anemia of varying severity.) A Hematocrit below 20 is significant and probably AIDS-defining; below 15 is severe, usually signaling approaching demise. It is sometimes the case that major drops in red cell values will precede major drops in WBCs. Gabriel, a cat belonging to Kaye Powelson, had been showing low-normal white counts with mild neutropenia when his hematocrit began plummeting into the low 20s and later the mid-teens; only subsequently did low WBCs and extreme neutropenia (and thrombocytopenia) develop.

  • For a more complete discussion of interpreting a CBC report generally and in relation to FIV and secondary diseases that may be related to FIV, click here. (“FIV and the CBC”)

  • 3. CD4+ (T4) Cell Counts.

  • The CD4+ (or T4) lymphocyte is, along with macrophages and, to a lesser extent, the CD8+ lymphocyte, the major target of FIV and the cell whose loss is primarily responsible for the loss of immune function. In HIV medicine, absolute counts below 500 to 350/mm3 are triggers for initiation of antiretroviral therapy. Counts below 200 are considered AIDS-defining and counts below 100 may, for instance, trigger preventative therapy against toxoplasmosis. However, CD4+ lymphocyte counts are only accurate determiners of FIV immune suppression if, at the time the blood sample was taken, the individual was not suffering from significant infections, sepsis, organ failure, shock, over-exertion, stress, and similar circumstances. Any of these have been shown to transiently impact CD4+ lymphocyte counts.

  • Veterinary virologists and immunologists regard CD4+ data as less predictive of immune function in FIV+ cats than is the case with HIV+ humans. Why this should be so is not clear, but it is not uncommon for European vets (T-cell testing is more common and readily available) to report clinically healthy cats with surprisingly low CD4+ cell counts. As the data following indicates, cats with similar clinical pictures can have varying CD4+ values, and cats with similar CD4+ values can have varying clinical pictures.

  • Absolute Counts.

  • CD4+ counts are often recorded as a percentage of all lymphocytes, although absolute counts are preferable. A recent Purdue University study found a mean percentage of 18.2% CD4+ cells in FIV+ cats, 33.9% in FIV- cats. The program that did Bud’s CD4+ testing did not provide absolute CD4+ counts. If an absolute count is not provided, divide the total lymphocytes in a concurrent CBC by the CD4%. The following are benchmark absolute counts commonly used in HIV medicine:
  •   
  • Normal--------------------------------800 to 1600/mm3
  • Moderate Suppression------------200 to 500
  • Significant Suppression------------50 to 200 (AIDS-defining)
  • Severe Immune Suppression----< 50

  • * The 500-800 range is a shadow area that might or might not be regarded as clinically significant.

  • Laboklin, a German laboratory, publishes the following normal ranges for lymphocytes of cats:
  •  
  • CD4+-------------------------------468-1638
  • CD8+-------------------------------311-1338
  • B Cell-------------------------------252-1068
  • T Cells------------------------------996-3166

  • The following mean counts were registered in a Japanese study of FIV+ cats. Stages were assigned at the outset of the study on the basis of observed symptoms.
  •  
  • AC (Asymptomatic) Stage---------------768 +/- 457 standard deviation
  • ARC (AIDS-Related Complex)----------450 +/- 336 sd
  • AIDS-------------------------------------------164 +/- 132sd

  • The good news is that the mean counts are clear and convincing about the overall relationship of CD4+ counts and disease progression. They also mirror the benchmarks used in HIV medicine. The bad new is that the standard deviations (that is to say, the average deviation from the mean in individual cats) are so large that in any given instance an absolute count alone is unreliable as a basis for fixing disease progression. The most that can be said of any cat with a count of , say, 400 is that it is more probably than not moderately immune-suppressed.

  • CD4:CD8 Ratio.

  • A normal ratio of CD4+ to CD8+ lymphocytes usually favors the former. As FIV progresses, CD4+ lymphocytes decline. CD8+ will increase as an overall percentage of T helper lymphocytes since their function is cytotoxic and directed against invading virus and since they are less a target for the virus than the CD4+ lymphocyte; their absolute numbers may decline slightly, but at a lesser rate than CD4+ lymphocytes. In the last disease stage CD8+ numbers collapse and the ratio is no longer relevant. The inability of CD8+ cytotoxic lymphocytes to control viral proliferation is considered a central event in disease progression to the terminal stage. The use of the ratio as a benchmark is as a hedge against skewing of absolute CD4 counts owing to natural variability and outside influences.

  •             >1 to 2.3-----------------------------Normal
  • .2 to .7-------------------------------Moderately suppressed
  • <.2------------------------------------Severely suppressed


  • * The .7 to 1.0 range is a shadow area that may or may not indicate moderate immune-suppression.

  • Laboklin, a German laboratory, publishes the following normal CD4+:CD8+ Ratios for cats: 0.81-2.00.

  • A German study of 26 FIV+ and 36 FIV- cats showed a mean ratio of approx. 1.5 in the FIV- cats, .75 in the FIV + cats. A more recent Purdue University study of 61 FIV+ and 143 FIV- cats showed a mean ratio of 1.63 to 1.72 in FIV- cats (the lower end of the mean range accounted for by cats with chronic non-FIV infections), 1.0 in FIV+ cats. Bud’s CD4:CD8 was .3 on the one occasion that this measure was taken. The ratio of Max, a cat belonging to Dianne Hayes, was the same. At the time Bud had a much higher WBC than Max; however, Max had a much higher percentage of lymphocytes than Bud. Clinically, both showed moderate disease progression.

  • A recent Purdue University study established that the ratio of CD4+ cells to a subset of CD8+ cells denoted as CD8low is a better indicator than to all CD8+ cells. The CD8low subset show molecular markers indicating activation in response to FIV. At present, However, this assay is confined to the experimental laboratory.

  • Note: Anergy. One thing that neither CD4 or CD8 counts or ratios measure is the state of immune responsiveness. Impairment of immune-system signaling (“cytokine dysregulation”) is a feature of FIV and HIV infection. Some part of the infective process–possibly the surface glycoprotein of FIV --is able to upregulate expression of molecules in CD4+ cells that leave them–and normal CD4+ and CD8+ cells they come in contact with–in a state of partial but incomplete activation. Proliferation of CD4+ cells in lymph nodes is dampened, as is effector function of cytotoxic CD8+ cell, and the partial activation allows apoptosis. Concomitantly, activation of CD4+CD25+ “suppressor” T-Regulatory Cells (Tregs) can induce a lack of responsiveness (anergy) in CD4+ and CD8+ T cells that renders cells present and accounted for as useless as if they were not there at all. HIV-induced anergy can be assessed with several different skin patch tests: the tuberculin test, the Multitest produced by Merieux that includes a tuberculin test along with antigens from a number of bacterial and fungal pathogens, and the DNCB test, which involves no antigen exposure at all. Cats have been characterized as having poor delayed hypersensitivity skin responses, which would seem to disqualify them as candidates for this otherwise attractive option for assessing immune competence. However, a 1993 study did find that Felocell FVRCP vaccine injected intradermally behind the ear produced a distinctive hypersensitivity response in immune-suppressed cats measurable by the thickness of skin at the injection site 72hrs. later. Whether this response would vary in a measurable way among cats with varying levels of immune suppression is unclear. The study in question concluded, “The application of FVRCP antigen delayed hypersensitivity testing to veterinary medicine needs to be explored. . . . There are potential benefits in using this test as part of a monitoring system when evaluating the need for and response to nutritional support, intensive care, and immunoregulatory therapy . . . . In addition to its use in the critical care population, the intradermal skin test may be useful as a prognostic aid and monitor of immune status for chronically infected FIV or FeLV cats.” There is no record of these findings ever having been explored further, either by the original researchers or by new ones.

  • For those wishing to convince their vet to run this test, click here for further information on how the test should be done ("A Skin-Patch Test for FIV Immune Competence").

  • CD4+ Cells as a % of Total Lymphocytes.

  • Some HIV specialists prefer these figures to either of the preceding. Below 15% is considered a trigger for antiretroviral therapy.
  •  
  • 20-40%--------------------------Normal Range
  • 14-19%--------------------------Moderate Immune Suppression
  • <14%----------------------------Significant to Severe Immune Suppression

  • Laboklin, a German laboratory, publishes the following normal values for cats.
  •  

  • CD4+ %------------------------26-42%
  • CD8+ %------------------------18-36%
  • T Cell %------------------------58-77%

  • CD4+ Analysis: An Example

  • The various CD4+ measures sometimes present a unified picture and sometimes do not. Probably the most consistent producer of variability is the presence of highly active pathological processes.

  • Poose, an FIV+ cat belonging to Martina Menz , had probably progressed clinically to the early AIDS stage of his illness prior to beginning antiretroviral therapy in September of 2002. The following four CD4+ lymphocyte counts were taken in 2003 after his having registered an lymphocyte count of 868 in September 2002 and a better1410 in January 2003.

  • Date--Lymphs----CD4+ Lymphs------CD4+ as % of Lymphs--------CD4:CD8 Ratio

  • 3/18—4320-------------670-----------------------15.5%---------------------------.6
  • 7/4----2900-------------391-----------------------13.4%---------------------------.84
  • 8/20—1974-------------405------------------------20.5%--------------------------.93
  • 10/8—3318-------------747------------------------22.5%--------------------------1.25

  • The blood work in which all three measures of CD4+ status are most in accord is the last. Not coincidentally, this was the period of the year when Poose’s health status was most stable. The middle two have an “aberrant” (high) CD4:CD8 ratio (7/4) and an “aberrant” (low) absolute count (8/20). It is probably not coincidental that a health crisis occurred during these months. One can speculate about the reason for the particular aberrations, but the point is that absence of outside influence seems to bring more coherent results. The first test produced a result nearly as coherent as the last. It came during a period of clinical stability that was nevertheless the result of an ongoing “improvement” phase.

  • Note: T:B Ratio. CD4+ tests may include information on B cells and T:B ratio. B cells are lymphocytes which differentiate into plasma cells that secrete antibody. In FIV- cats, T cells generally outnumber B cells so that the ratio is greater than 1.0. Although the German study previously mentioned shows that FIV+ cats have fewer B cells on average than FIV- cats, their T:B ratio is generally less than 1.0. Bud’s was .67 on the only occasion when he was tested. A low T:B ratio correlates with an overactive humoral response and is part of a larger picture of skewed balance associated with FIV infection. On serum chemistries, elevated levels of gamma globulin, a marker of B cell activity, are characteristic of FIV infection. The T:B ratio may actually tend to normalize with very advanced infection as a result of immune suppression of antibody synthesis. FIV-related cancers are notably B-cell in type and are probably related to chronic hyperstimulation.

  • 4. Viral Load.

  • Viral loads are done by a process called Real-Time PCR. Virus counts can be taken either at the free virus (RNA) level or at the embedded proviral (DNA) level; or both can be done, thereby providing a fuller view of the total cycle of replication. Since at any given time, some virus exists in “free” RNA form in plasma and some as integrated DNA provirus in cellular genes, knowing both counts helps to compensate for some of the effect of natural variability. Viral loads are most useful in multiples for monitoring disease progression or therapeutic progress. As a “snapshot” of immune status, a one-time viral load provides useful, but not always definitive, information. Viral load specimens should not be taken under conditions similar to those proscribed above for samples taken for CD4 counts.

  • Viral loads for cats with FIV may run in the millions/ml and are often expressed in logarithmic form in this way: 5.5 x 104 (=55,000). Each power (“4") added to the “10" signifies an additional zero. The limit of detctability in the previously mentioned Japanese study on FIV RNA viral loads was 950/ml. A smaller number of particles/ml would register as “undetectable.” The sensitivity of the better assays today may be as low as 5 to 50 viral particles/ml or cells/million. Natural variability in viral loads is usually measured by a multiple of 3, so that a count of 30,000 would not be considered “improvement” over a count of 50,000, but a count of 10,000 would. The counts provided in the Japanese study refer to RNA.

  • Viral Load and Stage of Disease .

  • AC Stage:
  • < 950 (Undetectable) / 38.4%
  • 104 Range/ 7.6%
  • 105 Range/ 38.4%
  • 106 Range/ 15.3%

  • ARC Stage:
  • 104 Range/ 12.5%
  • 105 Range/ 37.5%
  • 106 Range/ 50%

  • AIDS Stage:
  • 105 Range/ 18.1%
  • 106 Range/ 36.3%
  • 107 Range/ 36.3%
  • 108 Range/ 9.1%

  • The good new and bad news are the same as with CD4 counts. Overall, each stage of the disease is characterized by higher average viral loads. But the individual distribution covers four powers at both the AC and AIDS Stages and three powers at the ARC stage. It seems incredible (1) that AC and ARC Stages could have such similar viral load distributions once the “undetectables” are ignored, (2) that the 105 and 106 distributions should cover all three disease stages, and (3) that more than 1/3 of the asymptomatic cats registered viral loads under 1000, while at least some others registered viral loads as high as power 6. One perhaps unavoidable weakness in the design of the study is the assigning of stages based on observable symptoms at the outset of the study. As a practical matter, however, working with “donated” cats presumably left the researchers with few options. A second weakness is lack of control over the strain or substrain of virus. However, the general correlation of viral load and clinical health has been confirmed by numerous (1996, 2002, 2014) other studies.

  • Viral Load and Mortality Rates (Japanese Study)

  • The period of study was 46 months; survival calculations took in 41 months. All cats were provided standard veterinary support for secondary complications.

  • Viral Load >106------------Median Survival Time----------------2.5 Months
  • Viral Load <106------------Median Survival Time----------------41 Months
  • All Cats in Study-----------Median Survival Times----------------7 Months

  • Limited experience suggests that benchmarks derived from HIV medicine are useful tools for judging disease progression. Dianne Hayes’ cat Max had an RNA count of 73,751 at a time when his clinical history and bloodwork suggested moderate disease progression. Marcel Blanc’s cat Zouzou’s viral load of 160,000 RNA/ 140,000 DNA correlated with bloodwork and clinical signs pointing to progression to AIDS.

  • Viral Load and Disease Progression (HIV Guidelines)

  • >100,000--------------------Rapid Disease Progression
  • 10,000-100,000------------Average Disease Progression
  • <10,000---------------------Slow Disease Progression

  • Problems Associated with FIV Viral Load Testing

  • One particular problem with FIV viral load testing is documented by both the Japanese and German studies. Cats in the asymptomatic phase of infection frequently have undetectable viral loads, a feature not characteristic of HIV infection. In the Japanese study, of 13 cats designated asymptomatic, 5 had no measurable viral load.

  • Another problem is that data bases in even the most advanced facilities lack complete information on all FIV subtypes and, as a consequence, may produce inaccurate results. Gabriel, a cat belonging to Kaye Powelson, registered a minuscule 137 copies/ml RNA at a time when clinically and hematologically he was clearly either at or approaching the AIDS stage of infection. The only plausible explanation is that the PCR was not accurately attuned to his virus.


  • 5. Clinical Health

  • Most reliable vets have a credo that goes something like this: The labs are important, but if the labs are telling me something I am not seeing in a physical exam and history, then I may require some convincing. Because all of the laboratory tests for FIV immune status have areas of ambiguity, the clinical picture offers valuable information.

  • Staging.

  • FIV infection is usually divided into four stages: Acute (initial infection process), AC (asymptomatic carrier, ending with PGL, or persistent generalized lymphoadenopathy), ARC (AIDS-related complex), and AIDS. Some descriptions of the disease simply number the stages 1 through 4. Each stage has characteristic clinical features which can–and should–be factored into the analysis of whatever information is available from the three tests already dealt with. The acute stage, not being relevant to the immediate purpose, will not be dealt with. It is rare for a cat not to put the acute stage behind.

  • AC.

  • One of the many distressing features of FIV infection is that it is impossible project a time frame for clinical good health. Some cats begin showing symptoms within a few years; others go six, eight, ten years, or more without showing significant symptoms. Factors possibly responsible are listed on the “Contributing Causes of FIV Disease Progression” page. Some highly virulent strains of FIV have been discovered which cause a highly accelerated disease process, but these are very much the exception, not the norm. A cat determined by physical exam to be less than two years old and showing characteristic FIV-related pathologies almost certainly acquired the disease from its mother before, at, or shortly after birth; these cats likewise experience an accelerated disease process. For all other cats, the operative word is “years”–maybe a few, more likely many.

  • The point cannot be made strongly enough that a majority of Asymptomatic Carriers are basically healthy cats. Viral loads in peripheral blood cells or plasma will often be modest, low, or unmeasurable. CBCs will be largely indistinguishable from those of FIV- cats. Although CD4+ testing will show a CD4:CD8 ratio lower than that of other cats, it needs to be understood that a lower-than-normal CD4+ count is not a deadly threat to health as long as there are there are sufficient functional cells to perform their characteristic tasks. (Specific tests of the functionality of CD4+ cells are unavailable, but anergy skin testing for immune responsiveness can provide information about the ability to mount an immune response.) A number of studies have found that FIV+ cats, even asymptomatic cats, do have less efficient immune responses when challenged with opportunistic diseases. They become sicker and need more care, for instance, when infected with feline herpesvirus. However, they get over the acute phase of the illness in the same amount of time and shed no more virus than FIV- cats. Anecdotal accounts of households with mixed FIV+ and FIV- cats often report a lack of distinction in asymptomatic positives and uninfected negatives. Current AAFP Guidelines specify normal vaccination protocols for two years post-infection, and even this figure is a shot in the dark. One study of lab cats placed the range of clearly impaired lymphoproliferation (as indicated by response to Concanavalin A, a laboratory stimulant) at 25-44 months. The truth is, it is difficult to frame empirical standards for fixing the point at which immune function is sufficiently abnormal as to have a statistical impact on health.

  • People who worry that their AC FIV+ cat will be flypaper for every infection that comes their way or who panic when such a cat becomes ill in any way at all, worrying that infection may spin out of control, are assuming a view of immune status that has little empirical basis. Vets who ascribe every manner of abnormality in such a cat to immune deficiency are doing the same. In a comparison of asymptomatic FIV+ and FIV- cats, a Swiss study that followed newly infected cats for 6 ½ years found a number of minor disturbances to blood chemistry probably due to a hypermetabolic state (e.g., higher glucose), disturbed lipid metabolism (lower cholesterol, higher triglycerides), and immune complex deposition in kidney glomerula (higher urea, creatinine, protein, phosphorus), but the values remained within the normal reference range. Statistically, the FIV+ cats showed a greater tendency to suffer transient oral disease and diarrhea than the FIV- control group, but manifestations tended to be mild.

  • Note on PGL: Some descriptions of FIV staging treat persistent generalized lymphadenopathy as a distinct disease phase between AC and ARC stages, usually noting that it often passes unnoticed. Lymph nodes may become swollen for reasons other than FIV-infection, of course, but lymphatic swelling in episodic fashion may be seen from this point on in disease progression. The popliteal lymph nodes on the hind quarters are the most frequent site of initial enlargement. Vague and occasional (but not chronic) disease states may be observed. Cats who are no longer asymptomatic but who show isolated or transient symptoms are sometimes lumped in this category rather than the one that follows.

  • ARC

  • The “C” in ARC stands for “Complex,” a fact to be remembered. FIV+ cats get sick just as other cats do. Until pathologies are recurrent (or refractory) or occur in bundles, the temptation to apply the term ARC to the staging should be resisted. It has been objected with some justice that ARC is a term derived from HIV medicine and may be only a loose fit for cats with FIV. Characteristic FIV-related pathologies (to the extent that they are clearly understood) involve depressed, hyperactive, and skewed immunity. Diseases of the oral cavity and of the bowels, frequently seen in FIV+ cats, probably have at least as much to do with chronic immune activation and skewed expression of T cell subsets and T:B ratio (antibody-response dominance) as with CD4:CD8 ratio. Both problems tend to involve a complex interplay of infectious agents (including FIV itself), autoimmune, and allergic responses. Next to diseases of the oral cavity, upper respiratory infections (frequently with associated eye infections) are the most common FIV-characteristic diseases. Households with sizable cat populations are going to see respiratory infections, so isolated infections should not be seen as statements about disease progression or immune status. Any FIV+ cat showing recurrent or refractory diseases of these sorts should, for therapeutic purposes, be considered an ARC-stage, symptomatic cat, even though FIV- cats can suffer from these problems as well. Unusual abscesses and fungal/bacterial infections should always be given strong consideration as FIV-related, as should unusual internal (e.g., hemobartonella) or external (e.g., notoedric mange) parasitic infections. Neuropathies of the central and/or peripheral nervous system, loss of coordination, behavioral changes, or seizures may occur at any point of the ARC (or AIDS) stage. A variety of other problems may have a basis in the level of aberrant immune response characteristic of the ARC stage. Cats exhibiting these pathologies are, by comparison to AC cats, more likely to show new or advanced abnormalities in one or more of the three tests of immune status dealt with, but not necessarily in all.

  • Cancers may appear at any stage of FIV infection. It is not unusual for cats that have never shown FIV-related pathologies to show FIV-related cancers. Statistical liability of FIV+ cats to B-cell cancers, especially lymphomas, may accrue more to hyperstimulation of certain aspects of immune response than to a simple lack of T cells. (Unlike FeLV+ cats, FIV+ cats seldom demonstrate viral infection of tumor cells.) Squamous cell and mast carcinomas have a lesser statistical correlation to FIV infection, as do myelo- and lymphoproliferative cancers.

  • The ARC stage in FIV+ cats can be as variable as the AC stage, lasting for months or years. Some FIV+ cats do not seem to advance past the AC stage for whatever reason: misdiagnosis due to an unconfirmed false positive antibody test, a strain of virus lacking in virulence, genetic restriction factors are among numerous possible explanations. Others show isolated FIV-related pathologies, but not at a level that justifies the ARC label. This is, in part, because, as already noted, many “fiv-related” diseases such as chronic diarrhea and gingivostomatitis are also found in FIV-cats. FIV infection may provide an extra “push” into specific conditions for which other factors already dispose a cat. Other ARC-stage cats grade into the AIDS phase of infection.

  • AIDS

  • Among the most frequent search terms used in accessing this web site are “end stage FIV,” “FIV symptoms late stage,” “full blown AIDS,” and the like. People with an FIV+ cat showing symptoms of almost any kind of pathology are worried that it might now be approaching the end of its life. This is usually an overreaction. Sometimes even extremely sick cats recover good health. Clinically, classic AIDS presentation involves depression, ongoing fever, inability to respond effectively to antibiotic therapy, and a general failure to thrive. Serious collapse of at least one white cell type and/or red-cell volume is likely, although sometimes high white cell counts are seen. Undiagnosed cancers may account for at least some of the last. Diseases that accompany severe immune suppression, such as reactivated toxoplasmosis or hemobartonella, are most likely to occur at this stage of infection. Often the inability to respond to therapy normally effective against secondary diseases is the most notable clinical feature. A cat in the AIDS stage of FIV infection is within the last months -- often within the last weeks -- of its life.

  • 6. Some Testing Facilities in the U.S. and Europe

  • CBCs can be obtained routinely through whatever lab services your vet uses.

  • Viral Load Testing

  • DNA Counts
  • IDEXX Molecular Diagnostics Laboratory
  • IDEXX RealPCR™ Tests
  • 1-888-433-9987, option 2, option 4
  • www.idexx.com/animalhealth/laboratory/realpcr/index.jsp
  • In Charge: Dr. Christian M. Leutenegger
  • IDEXX holds an exclusive license from UC Davis to run diagnostic FIV PCR with newly updated Taqman technology, which it began offering in June 2009.

  • DNA Counts
  • Molecular Diagnostics Laboratory
  • College of Veterinary Medicine
  • Department of Pathobiology
  • 252-A Greene Hall
  • Auburn University, AL 36849-5519
  • Telephone: (334) 844-2648
  • Email: moleculardiagnostics@auburn.edu
  • In Charge: Dr. Bernhard Kaltenboeck
  • Formerly a reverse-transcription PCR, with copy number the total of plasma RNA copies, mRNA copies, and proviral DNA copies; recently, RT step has been eliminated and count is provirus only.


  • RNA and DNA Counts
  • Laboratoire d'analyses vétérinaires SCANELIS
  • Ecole nationale vétérinaire de Toulouse
  • 23, chemin des Capelles
  • 31076 Toulouse Cedex 3, France
  • Telephone : 05 34 50 50 90
  • Fax : 05 34 50 40 38
  • E Mail: scanelis@scanelis.com
  • In Charge: Mrs. Sophie Lafon

  • DNA counts
  • University of Bristol
  • Langford Veterinary Diagnostics ®
  • School of Clinical Veterinary Science
  • Langford House, Langford, Bristol, BS40 5DU
  • Telephone: 0117 928 9412
  • Fax: 0117 928 9613
  • http://www.bristol.ac.uk/vetpath/lvd/lvd.htm


  • CD4 Testing

  • Percentages and ratios only; absolute counts not provided
  • North Carolina State University
  • College of Veterinary Medicine
  • Clinical Immunology Laboratory
  • RoomB-324, 4700 Hillsborough St, Raleigh, NC 27606
  • Phone:919-513-6363
  • Fax: 919-513-6703
  • Contact: Linda English
  • E-Mail: Linda_English@ncsu.edu
  • http://www.cvm.ncsu.edu/dphp/labs/clinicalimmunologylab.html

  • Companion Animal Laboratory
  • BP 613
  • 1, Rue Salomon Rachi
  • 10088 Troyes Cedex, France
  • Tel: 03 25 73 81 20
  • Fax: 03 25 73 80 40
  • www.c-a-l.fr

  • Ratios only; absolute counts not provided
  • Laboratorio d'Analisi Veterinarie "San Marco"
  • via Sorio 114/c, 35141 Padova
  • Tel. 049/8561039 (Laboratory)
  • Fax 02 700 51 8888
  • E maillab@sanmarcovet.it
  • www.sanmarcovet.it/index_lab.asp?menu=49&menu1=&menu2=
  • Instructions: > immuinologia > Conta linfociti CD4 e CD8 e relativo rapporto

  • Viral Load and CD4 Testing

  • DNA and RNA counts
  • Absolute immune cell counts provided
  • Laboklin Labor für Klinische Diagnostik GmbH
  • Steubenstrasse 4
  • 97668 Bad Kissingen, Germany
  • Phone: 0049 97172020
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