Summary of Section 7: Diagnosis of FIP; Section 7.3: Laboratory Changes in FIP: Routine haematology and serum biochemistry  Routine haematological changes are not specific for FIP, but common abnormalities include lymphopenia, neutrophilia, sometimes with a left shift, and a mild-to-moderate normocytic, normochromic anaemia.  Serum biochemistry changes are more helpful and include hyperglobulinaemia, accompanied by hypoalbuminaemia or low-to-normal serum albumin and a low albumin to globulin (A:G) ratio of less than 0.4 (an A:G ratio of greater than 0.8 makes FIP very unlikely). Increased bilirubin levels in the absence of haemolysis or elevations of liver enzyme activity raise the suspicion of FIP.  Acute phase proteins (APPs) are produced in the liver in many inflammatory and non-inflammatory diseases; the major APP in cats is α1-acid glycoprotein (AGP), and moderately elevated serum AGP concentrations of greater than 1.5 mg/mL often occur with FIP. Another important APP in cats is serum amyloid A, more readily available in some countries, which is also markedly increased in cats with FIP. Cytology and biochemistry of effusions  FIP effusions are highly proteinaceous, with a total protein concentration greater than 35 g/L, consistent with an exudate, but with relatively low cell counts of less than 5 × 109/L cells, more consistent with a modified transudate; however, sometimes, cell counts rise to 20 × 109/L.  Cytology is pyogranulomatous, with macrophages, non-degenerate neutrophils and few lymphocytes. Thick eosinophilic (pink-red) proteinaceous backgrounds on cytology slides are often described. If cytology reveals a septic neutrophilia (typically with degenerate neutrophils containing bacteria), neoplastic cells or a marked lymphocyte population, other diseases are more likely.  The Rivalta’s test is a crude point-of-care assay to identify proteinaceous inflammatory exudates, which occur with FIP, but also septic peritonitis and lymphoma. If positive, effusion cytology can be helpful to discriminate between these causes. A negative Rivalta’s test, however, is more helpful to rule out FIP. To perform the Rivalta’s test, 8 mL of distilled water at room temperature and one drop of 98% acetic acid (or white vinegar) are mixed in a test tube, and then one drop of effusion is carefully placed or layered onto the surface of the solution. A positive result is indicated by the drop staying attached to the surface of the solution, retaining its shape with a connection to the surface, or floating slowly to the bottom of the tube as a drop or like a jellyfish. A negative test is indicated by the drop disappearing and the solution remaining clear. However, the interpretation of results can be subjective, and it can be hard to decide whether a result is positive or negative. Cytology of fine-needle aspirates (FNAs), cerebrospinal fluid (CSF) or aqueous humour samples, and biochemistry, if applicable  Typical FNA features of FIP are highly cellular samples containing the normal cell population of the sampled tissues with the additional presence of neutrophils, macrophages, plasma cells, and lymphocytes, consistent with pyogranulomatous inflammation. An examination of the CSF can show a pleocytosis, predominantly neutrophilic, mononuclear, mixed or pyogranulomatous in nature, with elevated protein concentrations. The cytology of aqueous humour can show pyogranulomatous or mixed inflammation with neutrophils with or without macrophages.