All newborn children are routinely tested for PKU (Guthrie test or test for phenylketonuria) with a small blood sample taken from the heel. A few extra blood drops taken at the same time is sufficient for the Twin-test. Application forms with instructions and twin test kits can be ordered from Danish Twin Test.

Older children and adults can be tested using a cheek swab or a small blood sample. Request an application form with instructions and twin-test kit from Danish Twin Test.