Direct Answer
Laboratory billing is governed by the Medicare Clinical Laboratory Fee Schedule (CLFS), which determines the maximum Medicare payment for each lab test CPT code. The CLFS rates were restructured by the Protecting Access to Medicare Act (PAMA) of 2014, which tied Medicare lab rates to the weighted median of private payer rates. PAMA rates are updated every 3 years based on reporting periods. The two most critical compliance elements in lab billing are: (1) CLIA certification — every laboratory that performs tests on human specimens must hold the appropriate CLIA certificate for the complexity of tests performed; and (2) ABN (Advance Beneficiary Notice) — when a Medicare patient requests a lab test that Medicare may not cover, an ABN must be signed before the test to enable patient billing if Medicare denies.
Table of Contents
Clinical Lab Fee Schedule and PAMA
The Medicare Clinical Laboratory Fee Schedule (CLFS) is the primary payment schedule for clinical lab services billed to Medicare Part B: CLFS structure: each clinical lab CPT code has a specific CLFS rate (the maximum Medicare payment amount); Medicare pays 100% of the CLFS rate — there is no coinsurance or deductible for clinical lab services under Medicare Part B (this is a unique feature of lab billing); PAMA reform: the Protecting Access to Medicare Act (PAMA) of 2014 mandated that CLFS rates be based on the weighted median of private payer rates rather than a historical cost-based approach; applicable laboratories (those with more than $12,500 in Medicare revenues from lab services in the data collection period) must report their private payer rates and volume data to CMS; CMS calculates the weighted median private payer rate for each test and uses this as the CLFS rate; PAMA phase-in and rate cuts: the PAMA rate cuts were phased in to reduce the shock to lab revenues; Congressional action has delayed and limited some PAMA rate reductions multiple times; as of 2026, the full PAMA rate adjustments are still being phased; keep current with the annual CLFS update, as PAMA rate changes affect lab revenue significantly; Advanced Diagnostic Laboratory Tests (ADLTs): ADLTs are lab tests cleared or approved by the FDA, intended to be used, and performed only by the original developer; ADLT pricing is set through a separate mechanism: the initial ADLT rate is set at the list price for the first 3 calendar quarters; subsequently transitioning to a weighted median private payer rate; new ADLTs receive a temporary unique code (often a proprietary laboratory analysis — PLA — code) during CMS coding review; Clinical Diagnostic Lab Tests (CDLTs): all other clinical lab tests paid under the CLFS; subject to standard PAMA reporting and rate-setting; Billing on Part B: lab services billed to Medicare Part B use CMS-1500 (or electronic equivalent); lab services provided in the hospital outpatient setting may be billed on the UB-04 with revenue code 300 (laboratory); inpatient lab services are included in the MS-DRG payment and not separately billable to Medicare Part A.
CLIA Certificate Requirements
The Clinical Laboratory Improvement Amendments (CLIA) of 1988 regulate all laboratories that test human specimens: CLIA certificate types: Certificate of Waiver: for laboratories performing only waived tests (simple tests with low risk of erroneous results); waived tests include CLIA-waived point-of-care tests such as dipstick urinalysis, glucose by meter, fecal occult blood, urine pregnancy, rapid strep; the CLIA-waiver certificate does not allow performance of non-waived tests; Certificate for Provider-Performed Microscopy (PPM): for physicians, midlevel providers, or dentists who perform certain microscopy procedures during a patient visit; includes wet mounts, KOH preparations, pinworm exams, urine sediment exams; Certificate of Compliance (CoC): for labs that perform moderate and/or high complexity tests; inspected every 2 years by CMS or a CMS-approved accreditation organization (CAP, Joint Commission, COLA, AAAHC); Certificate of Accreditation (CoA): for labs accredited by CMS-approved accreditation organizations; deemed status — meets CLIA requirements through accreditation; CLIA number on claims: ALL laboratory claims must include the performing laboratory's CLIA number; the CLIA number goes in Box 23 of the CMS-1500 (Prior Auth/Reference No.) field; claims without the CLIA number are rejected; CLIA compliance and test complexity: laboratories must only perform tests that match their certificate complexity level; performing high-complexity tests (PCR, next-generation sequencing, complex immunoassays) under a certificate of waiver is a CLIA violation; test complexity is classified by CMS based on the FDA 510(k) classification of the test system; Point-of-care testing in physician offices: physician offices with CLIA Certificate of Waiver can perform waived tests in-house and bill the appropriate CPT code; the CLIA number and POC test CPT code must appear on the claim; commonly billed POC tests: 87880 (strep A), 87804 (influenza A and B), 82962 (glucose), 81002 (urinalysis).
Common Lab CPT Code Families
Clinical lab CPT codes are organized into sections by test type: Chemistry panels and individual chemistry tests: 80047 — basic metabolic panel (BMP): Ca, CO2, Cl, Cr, glucose, K, Na, BUN; 80053 — comprehensive metabolic panel (CMP): BMP + albumin, total bilirubin, total protein, AST, ALT, ALP; 80061 — lipid panel: cholesterol, HDL, LDL (calculated), triglycerides; 84153 — PSA (prostate specific antigen); 84443 — TSH; 82040 — albumin; 82565 — creatinine; 82947 — glucose; 83036 — HbA1c; Hematology: 85027 — complete blood count (CBC) automated, without differential; 85025 — CBC with automated differential; 85610 — prothrombin time (PT/INR); 85730 — thromboplastin time, partial (aPTT); Immunology/serology: 86140 — C-reactive protein (CRP); 86200 — cyclic citrullinated peptide antibody (CCP); 86235 — ANA; 87340 — hepatitis B surface antigen (HBsAg); 86803 — hepatitis C antibody; Microbiology: 87040 — blood culture; 87070 — culture, bacterial, any source except urine, blood or stool; 87081 — culture, presumptive, pathogenic organisms; 87186 — susceptibility studies, microdilution or agar dilution, each antibiotic; Urinalysis: 81001 — urinalysis, automated, with microscopy; 81002 — urinalysis, non-automated, without microscopy; 81003 — urinalysis, automated, without microscopy; Drug testing: 80305/80306/80307 — drug test, qualitative by immunoassay (code depends on method); G0480-G0483 — drug test, definitive (quantitative) by chromatography or mass spectrometry; drug testing has high audit scrutiny — document clinical indication and medical necessity for each test ordered; Pathology and lab: 88300-88309 — surgical pathology codes by level; 88305 is the most commonly used surgical pathology level (routine tissue diagnosis).
Molecular Diagnostics and NGS
Molecular diagnostics is the fastest-growing and most billing-complex area of lab medicine: Molecular pathology CPT codes (Tier 1 — most commonly performed): 81176 — KRAS (Kirsten rat sarcoma) gene analysis; 81210 — BRAF gene analysis, targeted sequence analysis; 81245 — FLT3 gene analysis, targeted sequence analysis; 81246 — FLT3 gene analysis, internal tandem duplication variants; 81252 — GJB2 gene analysis, full gene sequence; 81228 — chromosomal microarray analysis; Molecular pathology Tier 2 codes: CPT 81400-81408 cover molecular pathology procedures organized by level of technical complexity; Tier 2 codes cover procedures not individually described in Tier 1; Proprietary Laboratory Analyses (PLA) codes: PLA codes are unique, non-stacking codes for specific proprietary tests that are not adequately described by existing CPT codes; examples include multi-gene cancer risk panels, liquid biopsy tests, pharmacogenomics panels offered by specific vendors; PLA codes appear in the CPT code set with the vendor's name in the code descriptor; Next-generation sequencing (NGS) for oncology: 81445 — solid organ neoplasm genomic sequence analysis panel, 5-50 genes; 81455 — solid organ neoplasm genomic sequence analysis panel, 51+ genes; comprehensive genomic profiling (e.g., Foundation Medicine CDx, Tempus xT) is billed using specific PLA codes; FDA companion diagnostic approvals are relevant to coverage determination; NGS coverage: Medicare covers NGS for advanced cancer (metastatic solid tumor or hematologic malignancy) when performed using a CMS-approved test (covered by Medicare's National Coverage Determination); clinical evidence of advanced cancer must be documented; medical necessity documentation: all molecular tests require ICD-10 codes supporting the indication; test ordering must be by a treating physician; test results must be used in patient management; ordering of molecular panels without a clear clinical indication documented is a high-audit-risk area (particularly drug testing panels and cancer risk panels ordered without documented family history or clinical criteria).
ABN Requirements and Specimen Collection
Advance Beneficiary Notices (ABNs) and specimen collection codes are essential operational billing components for labs: ABN requirements for lab tests: when a Medicare beneficiary requests a lab test that Medicare is likely to deny because it does not meet medical necessity criteria, the laboratory (or ordering physician) must provide the patient with a completed ABN before the test is performed; the ABN informs the patient that Medicare may not pay, and the patient must choose either: Option 1 — have the test and agree to be billed if Medicare denies; Option 2 — have the test but not be billed regardless; Option 3 — decline the test; the ABN must be specific to the test — "Medicare may not cover [specific test] because [specific reason]"; a blanket "Medicare may not cover this test" without specificity is not a valid ABN; Modifier GA — ABN on file: when a lab test has an ABN on file and is billed to Medicare with expected denial, append Modifier GA to the CPT code; Modifier GA notifies Medicare that an ABN was signed and enables billing the patient if Medicare denies; Modifier GY — non-covered service: for services that are not covered by Medicare under any circumstances (not a medical necessity issue), use Modifier GY (item or service excluded from Medicare benefit); an ABN is not required for Modifier GY services, but an ABN can be used for additional patient protection; Specimen collection codes: 36415 — collection of venous blood by venipuncture; 36416 — collection of capillary blood specimen (fingerstick); these are billable by the clinical lab or physician office collecting the specimen; the collection fee is separate from the lab test fee; Medicare pays a nominal collection fee in addition to the CLFS rate; Reference lab billing: when a physician office collects a specimen and sends it to a reference laboratory: the reference lab bills Medicare directly for the test; the physician office may bill for collection (36415); the physician office should NOT bill the test — only the performing lab bills for the test; unbundling by billing the test under the physician's NPI when a reference lab performs it is improper billing.
FAQ
What are the most common lab billing compliance issues that trigger Medicare audits?
Laboratory billing has been a consistent focus of Medicare audit activity, particularly for high-cost molecular diagnostics and drug testing panels. The most common compliance issues: Lack of medical necessity documentation for ordered tests: lab tests must be medically necessary for the patient's condition; ordering blanket panels (e.g., comprehensive metabolic panel on every patient regardless of clinical need, or 40-drug urine drug panels for every patient in a pain management practice) is the primary source of lab fraud enforcement; each test ordered must be supported by a documented clinical indication in the ordering physician's record; reflex testing protocols: labs that automatically run additional tests without a physician order (reflex panels) must have a documented standing order protocol; Medicare has strict rules about which reflexes are acceptable and which require individual orders; Unbundling of panels into component tests: when a panel code exists (e.g., 80053 for CMP), billing each component test individually instead of the panel code is improper coding and results in higher billing than the bundled panel rate; the panel rate must be used when all panel components are performed; Drug testing panel over-utilization: urine drug testing (UDT) is a high-priority audit target; common violations include: ordering comprehensive drug panels (G0480-G0483) at every visit without individual clinical justification; billing for more analytes than the patient's clinical situation warrants; billing definitive quantitative testing (G-codes) without prior presumptive (immunoassay) results that warranted confirmation; CLIA number missing on claims: a technical but systematic issue — claims without a valid CLIA number are rejected; Reference lab billing confusion: physician offices that send specimens to reference labs sometimes incorrectly bill the test themselves; only the performing laboratory bills the lab test to Medicare; Molecular test coverage without LCD adherence: billing advanced molecular diagnostics without verifying the applicable Local Coverage Determination (LCD) criteria is a common source of denials and post-payment recoupment.
How does the 340B program apply to outpatient laboratory services?
The 340B Drug Pricing Program primarily applies to outpatient drugs and biologicals, not to laboratory tests. However, some important intersection points exist between 340B and laboratory services in eligible covered entities: 340B scope — drugs and biologics only: 340B provides discounted acquisition prices for covered outpatient drugs purchased by eligible covered entities (disproportionate share hospitals, FQHCs, Ryan White clinics, and others); laboratory test reagents and kits are NOT covered outpatient drugs under 340B — the 340B discount does not apply to reagent acquisition costs for lab tests; What 340B does cover that intersects with lab: some diagnostic agents administered to the patient (not test reagents) may qualify as covered outpatient drugs; contrast media and radioactive tracers used in imaging studies at eligible entities may qualify; pharmacogenomics and companion diagnostic test implications: when 340B pricing applies to a drug (e.g., a targeted cancer therapy), and the companion diagnostic lab test is required to determine eligibility for that drug (e.g., EGFR mutation testing before gefitinib), the 340B savings on the drug are separate from the billing of the companion diagnostic lab test; the companion diagnostic lab test is billed at the standard CLFS rate; the drug may be purchased at 340B pricing by the eligible entity; Covered entity compliance for labs: covered entities that are also clinical laboratories must maintain complete separation of their 340B compliance documentation from their CLIA compliance documentation; 340B audits focus on drug diversion (the use of 340B drugs for ineligible patients) — not on lab services; laboratory services are separately audited under CLIA and Medicare billing compliance programs; Lab billing under hospital outpatient setting: when a lab test is performed in a hospital outpatient department that is a 340B covered entity, the lab test is billed on the UB-04 under the OPPS (for Part B outpatient hospital) or on the CMS-1500 (for independent labs) — 340B does not change how lab CPT codes are billed or paid.
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