How accurate is triple AFP test for down syndrome?

Not very. The triple screen will detect about 70% of mothers carrying babies with down syndrome, but it is only a screening test and does not diagnose down syndrome. There are many false positive tests ("abnormal" tests in women who are carrying babies that do not have down syndrome). A newer blood test for fetal dna in the mother's blood can actually diagnose down syndrome in women who are at higher risk.
About 70 percent. Triple screening test which includes AFP (alfa feto protein) level detects approximately 70 percent of fetuses affected by down syndrome.