CMS announced that a new modifier, L1 (separately payable lab test), is to be used to designate hospital outpatient laboratory claims, type of bill (TOB) 13X, that may be billed separately instead of bundled under the Outpatient Perspective Payment System (OPPS) bundling rules. Transmittal R2957CP explains that modifier L1 should be appended to laboratory outpatient claims, TOB 13X, in the following circumstances: 1. A Medicare patient receives only laboratory services on a date of service (DOS), no other hospital outpatient services were received on the same DOS. 2. A Medicare patient receives other hospital outpatient services on the same DOS as a laboratory test but the test is clinically unrelated to the other services and is ordered by a different health care practitioner. When the modifier is added, the test will be excluded from the OPPS bundle and may be billed separately by the hospital laboratory. The new modifier would not be used on a claim for non-patient tests, which would be billed as a 14X TOB. Non-patient tests are not considered hospital outpatient tests, a designation that has other implications for hospital laboratories in terms of who can bill for those tests. The CMS transmittal provides an implementation date of July 1 for the new modifierâ€™s use but the effective date of the unbundling policy is Jan. 1.