Many of our clients have struggled over the years with the effect of Local Coverage Determinations (LCDs) issued by their local Medicare Administrative Contractor (MAC) in Transmittals, FAQs and newsletters.  They can be found on each MAC's website, but they don't always cover the same topics, MAC to MAC; and they sometimes seem inconsistent with National Coverage Determinations (NCDs) which are available in the NCD manual. In 2019 the Supreme Court said in Azar v. Allina Health Services, that the government, in Medicare, must use a formal notice and comment period to issue a rule that creates a 'substantive legal standard', as for coverage. The controversy since has been what types of decisions fall into that category.  For example, when the split/shared visit rules were first published, they were not in regulation and after the Allina case, were withdrawn. (See AGG Note) The determination of what qualifies as a substantive legal standard is relevant not just to reimbursement and payment issues, but also in false claims cases.  The common wisdom had been that the government could not rely on sub-regulatory guidance for enforcement of its programs. The 9th Circuit in Agendia v. Becerra (July 2021), acknowledging Allina, has staked out a position that LCDs need not be published pursuant to notice and comment if they do not establish a substantive legal standard. The standard in the LCD at issue was that the services be 'reasonable and medically necessary'. The MAC uniformly refused to pay for Agendia's diagnostic testing because it did not meet that standard.  Interestingly, the statute itself sets forth the reasonable and medically necessary standard. But, the MACs have a lot of room for interpretation there. Taken together, this means LCDs can be imposed on providers without having been formally published subject to comments. These cases have also changed the way we do legal research. We now look for MedLearn Matters articles, newsletters, FAQs and other informal publications to inform our guidance. We suggest our clients do the same.