Question: what does the cell free dna test for

title: Cell-free fetal DNA
text: Matrix - assisted laser desorption / ionization - time - of - flight mass spectrometry ( MALDI - TOF MS ) combined with single - base extension after PCR allows cffDNA detection with single base specificity and single DNA molecule sensitivity . DNA is amplified by PCR . Then , linear amplification with base extension reaction ( with a third primer ) is designed to anneal to the region upstream from the mutation site . One or two bases are added to the extension primer to produce two extension products from wild - type DNA and mutant DNA . Single base specificity provides advantages over hybridization - based techniques using TaqMan hydrolysis probes . In 2008 , when assessing the technique , Ding et al found no false positives or negatives when looking for cffDNA to determine fetal sex in sixteen maternal plasma samples . In 2010 , Akolekar et al correctly detected the sex of ninety of ninety - one male foetuses using MALDI - TOF mas spectrometry . The technique had accuracy , sensitivity and specificity of over 99 percent . Epigenetic