An increase in neutrophils (>250 x 106L) is considered diagnostic of peritonitis (bacterial, tuberculous, pancreatic or malignant).
Protein levels >25 g/L (exudate) favour inflammatory or malignant ascites.
Amylase activity is increased in Pancreatitis.
Occasionally Lactate dehydrogenase isoenzymes may help to determine the cause of an exudate:
LD5 is derived from neutrophils;
LD2 and LD3 suggest malignancy; and
LD1 and LD2 are derived from red cells.
A negative culture does not exclude the diagnosis of bacterial Peritonitis.
Cytology may detect primary or metastatic malignancy.
Interpretation of borderline/low grade lesions may prove difficult in peritoneal washings and are therefore reported in conjunction with accompanying histology.