Despite significant improvements over former non-invasive tests, the detection rate for the Harmony^{®} Prenatal Test is not 100%. False-positive results may occure. Therefore the Harmony^{®} Prenatal Test should be regarded as a screening test and not a diagnostic test. A positive (abnormal) result should therefore always be confirmed by a second, diagnostic method (chorionic villus sampling or amniotic puncture) with a subsequent chromosome analysis.

False-negative results are also possible. This is more common for trisomy 13 and the analysis of DiGeorge syndrome (Microdeletion 22q11.2).

The Harmony^{®} Test detects around 30 out of 32 trisomy 13 cases in its current version. A summary of all previous studies on trisomy 13 revealed an average detection rate of 93,8% . Trisomy 13 is, however, relatively easy to detect in an ultrasound scan during first trimester screening.

The Harmony® Test is able to detect 75% of all 22q11.2 microdeletions, including those smaller than 3 Mb at a false-positive rate of 0.5% .