General Diagnostic tests in FIP cats

Haematology – the blood cell count

Typical features are a non-regenerative anaemia. This means a low red blood cell (RBC) count or packed cell volume (PCV), without signs of increased reticulocytes. Reticulocytes are immature red cells that the body releases in response to reduced blood counts.  There is also often a microcytosis – red blood cells are small. This is a sign of FIP but of other diseases where there is failure to produce red blood cells. This can be seen for example in Iron Deficiency, Inflammatory Bowel disease, Lymphoma and liver shunts.

Regarding the white cell counts, FIP cases typically have decreased lymphocyte counts and increased neutrophil counts. There can be a mild left shift of neutrophils – this is the release of immature neutrophils (band neutrophils for example)  into the circulation in response to infection.

An increased lymphocyte count makes FIP less likely.

Biochemistry tests

Changes as listed below increase the likelihood of FIP but they can all occur in other diseases.

  • Bilirubin – increased levels. This is a bile pigment that causes jaundice, and can be elevated in liver disease or blood disease.
  • ALT and AlkPhos -mild or moderate increases. These can occur in liver diseases, growth or bone disease, and very high levels make FIP less likely.
  • Globulins -increased levels. These are blood proteins which include antibodies released in response to infectious disease or immune reactive processes.
  • Albumin – reduced levels. These are blood proteins which may also be reduced when the liver fails to make them or when there are bowel diseases or protein losses from the kidneys.
  • Albumin : Globulin ratio  –  less than 0.4 increases suspicion of FIP; greater than 0.6  makes FlP less likely.
  • If serum protein electrophoresis (SPE) performed, we would expect a polyclonal gammopathy in FIP. Monoclonal gammopathy would point towards a tumour of white blood or bone marrow cells.
  • Alpha1-acid glycoprotein (AGP) – increased above 1.5-3.0 g/l – This is an inflammatory disease marker found in the blood. Lower levels make FIP unlikely.

Immunology testing

FCoV antibody levels – high levels are present in many normal cats including almost 100% of cats with FIP. Absence of antibodies usually indicates rare cat that has never been exposed to FCoV, making FIP very unlikely. This is really the sole use of FCoV antibodies in diagnosis of FIP – that is ruling out FIP based on a negative result.

Imaging Results

Ultrasound or X-rays of chest or abdomen revealing fluid around heart, in chest or abdomen or multiple sites increases the likelihood of FIP. These changes can be seen in heart disease, lymphoma/other cancers  or occasionally liver/bowel disease.

Characteristics of “typical” FIP effusions

  • A high protein effusion (>35g/l) 
  • Albumin:Globulin ratio of <0.4 
  • Pale yellow to straw colour, sticky, odourless
  • Low cell count (<5×10^9/l) or moderate (<20 x10^9/l)
  • AGP >1.5mg/ml
  • Non degenerate neutrophils, macrophages and perhaps a few lymphocytes

Features that make FIP unlikely in fluid tests

  • Protein<25 g/l 
  • A:G ratio of >0.8
  • Cell count >20 x10^9/l
  • Toxic neutrophils and bacteria
  • Neoplastic ( cancer) cells
  • Markedly high lymphocyte or neutrophil count