MODIFIER 91 Definition.
CPT® defines Modifier 91 as a repeat clinical diagnostic laboratory test. It implies when successive lab procedures are conducted on the same patient on the same day to acquire additional test data throughout therapy. You can see why it’s critical to include suitable modifiers when billing the same CPT twice or three times on the same day for the same patient. Consider the claim from the payer’s point of view; it appears to be a copy of services, resulting in an instant denial of these claims.
