Anti-streptolysin O or ASO is a group of antibodies that the body creates in response to streptolysin, a toxic substance created by the Gram bacteria, streptococci. An elevated level of the ASO antibodies in the blood indicates the presence of a serious infection. The ASO titre test is conducted to check for a strep infection caused by these bacteria. A strep infection leads to the condition of either a kidney disease named glomerulonephritis or rheumatic fever. The ASO titre test detects either of these conditions and examines the extent of the infection. The doctor provides different treatment according to the results.