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ASO Titer test and fasting


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Just an FYI - I was googling ASO titer test to fact-check something and I went to the NIH Medline Plus site



It states that you should not eat anything for 6 hours prior to the test. I never knew this and now wonder if this had anything to do with my son's false negative result 3 weeks after a confirmed rapid strep test with blisters on his throat and scarlet fever. Or maybe he's among the 37% whose levels don't rise above levels that are "normal" for most of the population. May never know.


But when I went looking for why you need to fast, I found this explanation



An excerpt:

For the ASO test, increased levels of fats, called beta lipoproteins, in the blood can neutralize streptolysin O and cause a false-positive ASO titer. Antibiotics, which reduce the number of streptococci and thereby suppress ASO production, may decrease ASO levels. Steroids, which suppress the immune system, consequently may also suppress ASO production. Also Group A streptococcal infections of the skin may not produce an ASO response. Antibiotics also may decrease anti-DNase-B (ADB) levels.


These antibody tests are useful for group A streptococci. Group A streptococci are the most virulent species for humans and are the cause of strep throat, tonsillitis, wound and skin infections, blood infections (septicemia), scarlet fever, pneumonia, rheumatic fever, Sydenham's chorea (formerly called St. Vitus' dance), and glomerulonephritis.


...ASO appears in the blood serum one week to one month after the onset of a strep infection. A high titer (high levels of ASO) is not specific for any type of post-streptococcal disease, but it does indicate if a streptococcal infection is or has been present.

....The diagnosis of a previous strep infection is confirmed when serial titers of ASO rise over a period of weeks, then fall slowly. ASO titers peak during the third week after the onset of acute symptoms of a streptococcal disease; at six months after onset, approximately 30% of patients exhibit abnormal titers.

Antideoxyribonuclease-B titer (anti-DNase B, or ADB)


Anti-DNase-B, or ADB, also detects antigens produced by group A strep, and is elevated in most patients with rheumatic fever and poststreptococcal glomerulonephritis. This test is often done concurrently with the ASO titer, and subsequent testing is usually performed to detect differences in the acute and convalescent blood samples. When ASO and ADB are performed concurrently, 95% of previous strep infections are detected. If both are repeatedly negative, the likelihood is that the patient's symptoms are not caused by a poststreptococcal disease.


When evaluating patients with acute rheumatic fever, the American Heart Association recommends the ASO titer rather than ADB. Even though the ADB is more sensitive than ASO, its results are too variable. It also should be noted that, while ASO is the recommended test, when ASO and ADB are done together, the combination is better than either ASO or ADB alone.


I wish this was from a source I could validate - I have no idea what "stateuniversity.com" is - but I found the full explanation on this site helpful and thought I'd pass it along for what it's worth.

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