Yellowish staining of the skin is a sign of overt jaundice, and overt jaundice is defined as bilirubin in the serum reaching 34.2 μmol/L or more.
In addition to overt jaundice, there is also occult jaundice, which refers to serum bilirubin of 17.1 to 34.2 μmol/L and no yellow staining of the skin.