Blood Biomarkers Improve Alzheimer's Disease Diagnosis Accuracy

Antistreptolysin O, commonly known as ASO, is a blood test that measures antibodies produced by the immune system in response to an infection caused by Group A Streptococcus bacteria. These bacteria are responsible for various infections, including strep throat, scarlet fever, and skin infections. When the body encounters these bacteria, it produces antibodies against streptolysin O, a toxic substance released by the streptococcal bacteria. The ASO test detects and measures the level of these antibodies in the blood.

The primary purpose of the ASO test is to determine whether a person has recently had a streptococcal infection, particularly when complications are suspected. This test is especially useful in diagnosing post-streptococcal complications such as rheumatic fever and post-streptococcal glomerulonephritis, a type of kidney inflammation. These conditions can develop weeks after the initial streptococcal infection has resolved, even if the original infection was mild or went unnoticed. The ASO test helps healthcare providers establish a connection between current symptoms and a previous streptococcal infection.

ASO antibody levels typically begin to rise about one week after a streptococcal infection and reach their peak between three to five weeks after the infection. The antibodies can remain elevated for several months before gradually declining. A single elevated ASO result indicates exposure to streptococcal bacteria, but it does not necessarily mean there is an active infection. For this reason, healthcare providers often order two ASO tests taken two to four weeks apart to observe whether antibody levels are rising, which would suggest a recent infection.

Normal ASO levels vary depending on age and the laboratory performing the test, but generally, values below 200 units per milliliter are considered normal for adults. Elevated ASO levels suggest a recent streptococcal infection, though the degree of elevation does not necessarily correlate with the severity of the infection or complications. It is important to note that not everyone who has a streptococcal infection will develop elevated ASO levels, and some people may have elevated levels without having had a recent infection. The test results should always be interpreted in conjunction with clinical symptoms and other diagnostic findings.