Medicare Lab Billing Basics for Clinical Laboratories
To bill Medicare for lab tests, a lab needs a CLIA certificate covering each test. Every claim carries the 10-character CLIA number, plus the QW modifier where CMS requires it for waived tests. Tests must be ordered by the treating practitioner and be reasonable and necessary. Medicare pays them under the CLFS without cost-sharing.
Sound Lab Consultants (SLC) offers clinical lab billing nationwide. This overview summarizes CMS guidance. Your MAC's instructions control.
1. CLIA comes first
CMS MLN006270, "CLIA Program & Medicare Lab Services" says Medicare pays only for tests that fall within the lab's CLIA certificate. The 10-character CLIA number must be on all lab claims. Claims Processing Manual Ch. 16 § 70.10 explains where it goes: the 837P REF segment (qualifier X4), or item 23 of the paper CMS-1500. For certificate types, see what is CLIA.
2. Waived tests and the QW modifier
Labs with a Certificate of Waiver can bill only waived tests. CMS requires the QW modifier on certain waived test codes so its systems recognize them as waived. Check the CMS list of waived tests that need QW, which CMS updates through change requests.
3. Orders and medical necessity
Tests must be ordered by the treating physician or a qualified NPP, under 42 CFR 410.32(a). They also have to meet coverage rules. See Medicare lab NCDs and LCDs.
4. Payment and cost-sharing
Medicare pays most tests under the Clinical Laboratory Fee Schedule. Under Ch. 16 § 30.2, no Part B deductible or coinsurance applies to assigned lab tests, specimen collection fees, or travel allowances. Accept assignment as Ch. 16 requires.
5. Date of service
Under 42 CFR 414.510 and the CMS Date of Service Policy page, the date of service is generally the date the specimen was collected. There are exceptions:
the 14-day rule, for specimens from hospital inpatients or outpatients that are tested after discharge, and
the ADLT and molecular pathology exception (effective January 1, 2018). When it applies, the date of service is the date the test was performed, and the performing lab bills Medicare directly.
6. Coding and edits
HCPCS and CPT codes identify each test. ICD-10-CM codes support medical necessity.
NCCI edits catch code pairs that shouldn't be billed together and set medically unlikely edits (MUEs) for units.
Denials come back with CARC and RARC codes. Use them to work the denials.
7. ABNs
When you expect Medicare to deny a test as not reasonable and necessary, give the patient an ABN before testing, per Claims Processing Manual Ch. 30.
8. Enrollment and your MAC
The lab must be enrolled in Medicare through PECOS and have an NPI. Claims go to your MAC, usually electronically on the 837P. For more CMS lab resources, see the CMS Clinical Labs Information Center.
Medicare lab billing checklist
☐ Your CLIA certificate type covers every test you bill.
☐ The CLIA number goes on every claim (837P REF X4 or CMS-1500 item 23).
☐ The QW modifier is applied where CMS requires it.
☐ The ordering practitioner and diagnosis are captured for each test.
☐ NCD and LCD checks run before you submit, and ABNs are issued when needed.
☐ The date of service follows § 414.510, including the 14-day and ADLT/molecular exceptions.
☐ NCCI and MUE edits are checked before submission.
☐ No deductible or coinsurance is charged on assigned CLFS tests.
☐ CARC/RARC denial trends are reviewed every month.
☐ PECOS enrollment and NPI data match what's on your claims.
FAQs
Where does the CLIA number go on a Medicare claim?
In the 837P REF segment with qualifier X4, or in item 23 of the paper CMS-1500 (Claims Processing Manual Ch. 16 § 70.10).
What is the QW modifier?
A HCPCS modifier CMS requires on certain codes for CLIA-waived tests so they process as waived.
What date of service do I use for lab tests?
Generally the date the specimen was collected. The 14-day rule and the ADLT/molecular exception change this in specific cases (42 CFR 414.510).
Do Medicare patients owe coinsurance on lab tests?
Not for assigned clinical lab tests paid under the CLFS (Ch. 16 § 30.2).
Who can order lab tests for Medicare patients?
The treating physician or a qualified nonphysician practitioner, under 42 CFR 410.32(a).
Why was my lab claim denied?
Common causes include a missing or mismatched CLIA number, tests outside the certificate, a diagnosis that doesn't support coverage, or NCCI edits. The CARC and RARC codes on the remittance point to the reason.
Does SLC handle lab billing?
Yes. SLC offers clinical lab billing and medical billing services.
Sound Lab Consultants Mailing address: PO Box 2135, Chandler, AZ 85244