CPT® Code 84450

Quick Reference

• Code definition: CPT 84450 reports a quantitative enzymatic measurement of aspartate aminotransferase (AST), formerly known as SGOT, performed on serum or plasma obtained by separately reportable venipuncture.
• Key billing rule: 84450 is a component of the Hepatic Function Panel (80076) and the Comprehensive Metabolic Panel (80053); when all panel components are performed, report only the panel code [4].
• Modifier essentials: Append QW when the test runs on a CLIA-waived device under a Certificate of Waiver; append 91 for a medically necessary repeat on the same calendar day. Modifiers 26 and TC do not apply (PC/TC Indicator = 9) [1].
• Documentation must-have: A clinical indication tied to the patient's active problem list or medication regimen. "Routine" or "annual bloodwork" language without a specific diagnosis fails medical necessity screening under most MAC LCDs.
• Top confusion point: Billing 84450 alongside 80053 or 80076 on the same date constitutes unbundling and is one of the most commonly flagged laboratory audit findings [4].
• Payer alert: Payment routes through the Clinical Laboratory Fee Schedule (CLFS), not the Physician Fee Schedule (MPFS). The ordering physician does not separately bill for interpreting a standalone chemistry result; that interpretation is subsumed by the E/M [2].
• CLIA status: CLIA waived. Facilities operating under a CLIA Certificate of Waiver must append modifier QW to receive Medicare reimbursement when using a waived device [5].

When to Use This Code

CPT 84450 covers any quantitative AST measurement performed on serum or plasma, regardless of setting (office lab, independent reference lab, hospital outpatient, or inpatient). The test is ordered in three broad contexts.

Liver disease workup and monitoring: AST elevation is a sensitive indicator of hepatocellular injury. The code supports claims for viral hepatitis (acute and chronic), alcoholic liver disease, non-alcoholic steatohepatitis (NASH/NAFLD), cirrhosis, drug-induced hepatotoxicity, and ischemic hepatitis. The AST to ALT ratio adds diagnostic weight: a ratio greater than 2:1 with both enzymes elevated is a classic marker for alcoholic liver disease, while an isolated AST elevation disproportionate to ALT points toward muscle or cardiac sources rather than hepatocellular injury [1].

Pre-treatment baseline and medication monitoring: AST must be documented before and during therapy with hepatotoxic agents including statins, methotrexate, isoniazid, antiepileptics, and antifungals. Serial monitoring of a patient on atorvastatin every 3 to 6 months is a high-volume billing scenario. Each date of service requires a documented clinical rationale tying the test to the specific agent being monitored.

Muscle and cardiac injury: AST is not liver-specific. Myocardial infarction, rhabdomyolysis, and myositis all release AST into circulation. When the clinical context points to muscle rather than liver, the diagnosis code must reflect that source and support the medical necessity of the test.

Scope note: The blood draw is separately reportable by the drawing facility using 36415 (venipuncture, age 3 and older) or 36416 (capillary collection). The laboratory performing the analysis bills 84450; the ordering physician does not.

Code Differentiation Table

The critical differentiator is component count. If a provider orders AST and ALT only, bill 84450 and 84460 separately. If the same provider orders the full hepatic panel and all 7 analytes are resulted, 80076 replaces the individual codes. Billing individual components when the complete panel was performed is just as problematic as unbundling; it undercodes revenue and often reflects a chargemaster configuration gap [4].

Billing & Modifier Rules

Modifier QW: Any facility holding a CLIA Certificate of Waiver must append QW when billing Medicare for 84450 performed on an FDA-approved waived analyzer. Omitting QW on a waived-device claim triggers denial because the payer cannot confirm the facility holds the appropriate CLIA certificate level [5].

Modifier 91: The MUE for 84450 is 1 under normal circumstances [4]. When serial AST monitoring is medically necessary on the same calendar day (e.g., every 6 hours in suspected acetaminophen toxicity), append modifier 91 to each subsequent unit. Modifier 91 is not appropriate when the first result was unsatisfactory due to equipment failure or specimen quality.

Modifiers that do not apply:

• 26 / TC: PC/TC Indicator = 9; this code has no professional or technical component split [1].
• 50: Bilateral concept does not apply to laboratory analytes.
• 51: Multiple procedure reduction does not apply.

Panel bundling [4]:

• 84450 cannot be billed on the same date as 80053 or 80076.
• 84450 cannot be billed on the same date as 80050, which subsumes 80053.
• When fewer than all panel components are performed, report individual analyte codes; never bill the panel code for a partial set of results.

Hospital outpatient (OPPS): APC Status Indicator = "Conditionally packaged laboratory tests." In an OPPS setting, 84450 may be packaged into the payment for the primary service; it is only paid separately when it is the primary or sole service billed on the claim [2].

Venipuncture billing: The entity that performs the draw bills 36415. If a physician office draws and sends to a reference lab, the office bills 36415 and the reference lab bills 84450. Neither bills the other's component.

Documentation Essentials

Required elements for 84450:

• Ordering provider identity and treating relationship to the patient
• Clinical indication or diagnosis supporting the need for AST measurement on that specific date of service
• Specimen source (serum or plasma) and date of collection
• Test result with evidence the treating provider reviewed and acted on the finding

Audit red flags for this code specifically:

• "Routine labs" or "annual bloodwork" without a linked problem or active medication on the problem list; this language fails medical necessity screening under most MAC LCDs [3].
• Serial 84450 claims without documentation of the clinical reason for each repeated test. "Monitoring" alone is insufficient; the record must state what is being monitored, why repeat testing is necessary, and how the prior result informed the next order.
• 84450 billed by an ordering physician who sent the specimen to an outside reference lab. A lab bill and an ordering physician bill for the same analyte on the same date trigger duplicate claim edits.
• Claims pairing 84450 with 80053 or 80076 on the same date; post-payment audits specifically target this combination.

For medication monitoring claims: The medical record must identify the specific drug (e.g., "atorvastatin 40 mg"), the duration of therapy, and the clinical rationale for testing frequency. Z79.899 (long-term use of other medication) is the appropriate diagnosis when no hepatic disease has been diagnosed, but it must be supported by documentation of the specific agent [3].

Medicare, Commercial & Medicaid Payer Rules

Medicare:

84450 carries Statutory Exclusion status from the MPFS; payment flows through the CLFS with rates updated annually under the PAMA methodology. CMS uses private payer rate data to set CLFS rates; current-year rates require verification at the CMS CLFS page [2].

Most Medicare Administrative Contractors have issued LCDs covering automated chemistry tests. Common covered indications include liver disease monitoring, viral hepatitis management, suspected drug hepatotoxicity, pre-operative evaluation, alcohol use disorder monitoring, and metabolic syndrome assessment [3]. There is no universal frequency limitation for 84450 under Medicare; coverage is determined claim by claim on medical necessity. Some MACs include specific frequency guidance in their LCD articles; the applicable MAC's LCD article should be reviewed for the beneficiary's jurisdiction.

ABN requirements: If 84450 is ordered and there is reason to believe Medicare will not cover it (no qualifying diagnosis, screening context without documented risk factors), issue an Advance Beneficiary Notice of Non-Coverage before the test is performed. File modifier GA (ABN on file) or GY (service meets a statutory exclusion) as appropriate [6].

Commercial payers:

Commercial payer policies generally mirror the panel bundling logic, but prior authorization requirements and frequency limitations vary significantly. Standalone 84450 for medication monitoring is typically covered without prior authorization when accompanied by an appropriate diagnosis code, but documentation requirements mirror Medicare's medical necessity standard.

Medicaid:

Medicaid and managed Medicaid plans may apply state-specific frequency caps or require a qualifying ICD-10-CM code from a defined covered diagnosis list. Verify with the applicable state fee schedule and any contracted managed care plan policies.

Common Denials & Prevention

Unbundled panel component

Panel NCCI edits fire automatically when 84450 appears on the same claim as 80053 or 80076 [4]. This occurs when laboratory information systems generate charges at the analyte level and the billing system does not roll up to the panel code. Prevention: configure the chargemaster or LIS to suppress individual analyte codes automatically when all panel components are resulted on the same accession. For post-payment denials, appeal is unlikely to succeed unless documentation shows only partial panel components were performed; if that is the case, refile with individual analyte codes and attach the original order.

Missing or incorrect CLIA modifier

Medicare denies 84450 when a CLIA-waived facility omits modifier QW [5]. Prevention: build QW into the charge description master for all analytes performed on waived devices, keyed to the specific analyzer. Corrected claims with QW added timely are generally accepted within the filing limit.

Insufficient medical necessity

The claim passes NCCI but denies at the LCD level because no covered diagnosis appears on the claim or the record lacks a documented clinical indication. Prevention: ensure the ordering provider links 84450 to a specific ICD-10-CM code from the MAC's covered diagnosis list at the time of order. R74.01 (elevation of liver transaminase levels) is acceptable when a specific etiology is not yet confirmed, but the most specific available code should be used when a diagnosis is established [3].

Ordering provider billing the lab analyte

Physician offices that send specimens to reference labs and then also bill 84450 create duplicate claim scenarios. Prevention: implement a billing policy restricting 84450 to the performing laboratory. The ordering physician's reimbursement for clinical review of lab results is captured through the E/M, not a separate lab code.

Same-day repeat without modifier 91

A second 84450 on the same date without modifier 91 triggers the MUE of 1 and is denied [4]. Prevention: append modifier 91 to every subsequent same-day unit and attach documentation of the clinical rationale at claim submission, particularly for inpatient or observation claims where serial monitoring is common.

Coding Scenarios

Scenario 1: Standalone AST and ALT for statin monitoring

A 58-year-old patient on atorvastatin presents for a 3-month follow-up. The provider orders AST and ALT only to screen for statin-induced hepatotoxicity. Both tests are resulted.

Correct coding: 84450 + 84460; diagnosis Z79.899

Why: Only two analytes were ordered and performed. Billing 80076 when only AST and ALT were performed is upcoding; all 7 panel components must be resulted to report the hepatic function panel.

Scenario 2: Full hepatic function panel for hepatitis C monitoring

A 45-year-old with chronic hepatitis C presents for quarterly liver function assessment. The provider orders albumin, total bilirubin, direct bilirubin, alkaline phosphatase, total protein, ALT, and AST. All 7 analytes are resulted.

Correct coding: 80076 only; diagnosis B18.2

Why: All 7 components of the hepatic function panel were performed. Billing 84450 and 84460 alongside 80076 constitutes unbundling and triggers NCCI edit denial [4].

Scenario 3: Serial AST monitoring in acetaminophen toxicity

A hospitalized patient with suspected acetaminophen overdose has an initial AST drawn at 8:00 AM. The hepatologist documents the clinical necessity for serial AST every 6 hours to detect progression to fulminant hepatic failure. A second draw is performed at 2:00 PM.

Correct coding: 84450 at 8:00 AM; 84450-91 at 2:00 PM; diagnosis K71.10

Why: The MUE of 1 applies to the first unit. Modifier 91 supports the second unit by indicating a medically necessary subsequent result rather than a repeated test due to specimen failure. Documentation must explicitly state why same-day serial testing was clinically necessary [4].

Scenario 4: CLIA-waived CMP on point-of-care analyzer

An outpatient clinic holds a CLIA Certificate of Waiver and performs a CMP on an FDA-approved waived analyzer for a patient with type 2 diabetes on metformin. All 14 CMP components, including AST and ALT, are resulted.

Correct coding: 80053-QW; diagnosis E11.9

Why: The QW modifier applies to the panel code because the waived device performed all panel components. Neither 84450 nor 84460 should be billed alongside 80053 on the same date [5].

Related Codes

• 84460 (ALT/SGPT): Complementary aminotransferase; almost always ordered with 84450; AST to ALT ratio carries independent diagnostic significance
• 80076 (Hepatic function panel): The 7-component panel containing 84450; replaces standalone 84450 when all components are performed
• 80053 (Comprehensive metabolic panel): 14-component panel that includes both 84450 and 84460; CLIA waived
• 82977 (GGT): Co-ordered in liver workup; helps distinguish alcohol-related from other hepatic etiologies; CLIA waived
• 84075 (Alkaline phosphatase): Biliary and bone marker ordered alongside AST/ALT; component of both 80076 and 80053
• 82247 (Bilirubin, total): Component of the hepatic function panel; paired with AST in hepatic workup
• 36415 (Venous blood collection by venipuncture): Separately reportable by the drawing facility for the blood draw that yields the specimen for 84450

Sources

1. CPT Code Set, AMA — Official CPT code descriptions and panel component rules for 84450, 84460, 80053, and 80076 (updated annually)
2. Clinical Laboratory Fee Schedule, CMS — CLFS payment rates for 84450; PAMA rate-setting methodology (updated annually)
3. Medicare Coverage Database, CMS — LCD policies covering automated chemistry tests including AST; MAC-specific covered diagnosis lists
4. NCCI Policy Manual for Medicare Services, CMS — Panel bundling edits; MUE values; NCCI PTP edit rules for 84450 (updated quarterly)
5. CLIA Waived Tests List, CDC — CLIA-waived status for 84450 testing devices; QW modifier requirements
6. ABN Instructions, CMS Medicare Learning Network — ABN issuance requirements; modifier GA and GY usage for laboratory services