CPT Code 33533 You’re Guide to Accurate CABG Billing & Avoiding Denials

Q: What ICD-10 codes are commonly linked with 33533?

I25.10 – Atherosclerotic heart disease of native coronary artery I20.0 – Unstable angina

Q: What is the difference between CPT 33533 and 33518?

33533: Venous graft only 33518: Arterial graft only

CPT code 33533 is used for CABG with venous graft only, covering a single coronary artery.
Bill 33533 multiple times (e.g., x2, x3) for multiple venous grafts.
Do not confuse with 33510 (venous + arterial) or 33518 (arterial-only).
Use modifiers (-59, -LC, -LD) to prevent denials for distinct grafts.
Always document graft sources, harvest methods, and ICD-10 linkage.
Average reimbursement ranges $2,300–$2,800 depending on payer.
Denials are often caused by missing modifiers, unbundling, or incorrect units.

As a cardiac surgery billing specialist for more than a decade, I’ve seen firsthand how a single error in selecting CPT code 33533 can lead to delayed reimbursements, claim denials, or compliance risks. This code is central in billing for coronary artery bypass grafting (CABG) procedures, specifically when a venous only is used.

What is CPT Code 33533?

CPT code 33533 is defined as:

Coronary artery bypass, using venous graft(s) only; single coronary venous graft.

Key details:

CABG Type: Venous graft only (e.g., saphenous vein).
Number of Bypasses: One graft (report multiple units for multiple venous grafts).
Excludes: Arterial grafts (those fall under different CPT codes).

Common Mistakes with CPT 33533

Billing errors with CPT 33533 often stem from:

- Confusion with 33510 or 33518:
  - 33510 = venous + arterial graft
  - 33518 = arterial-only graft
- Incorrect Units: Billing 33533 once for CABG x3, instead of 33533 x3.
- Missing Modifiers: Failure to append -59 when reporting distinct venous grafts.

CPT 33533 vs. CABG Codes

Here’s a comparison table:

CPT Code	Description
33533	Venous graft CABG, single coronary artery
33510	CABG using venous + arterial grafts
33518	CABG using arterial grafts only
33517	Vein harvest (upper extremity, report separately)
33519	CABG using combined arterial and venous grafts

Pro Tip: For CABG x2 or CABG x3, bill 33533 multiple times (e.g., 33533 x3 for three venous grafts). For mixed grafts, combine 33518 + 33533.

Can CPT 33508 and 33533 Be Billed Together?

Yes, but only if:

33508 (arterial CABG) and 33533 (venous CABG) are performed on different vessels.
Modifier -59 is appended to show the procedures are distinct.

Denial Alert: Payers often reject claims when modifiers are missing.

Avoid Denials - 5 Actionable Tips

Document Sources – Clearly specify venous vs. arterial and harvest sites.
Use Modifiers Wisely – Apply –59, -LC, -LD as appropriate.
Bill Units Correctly – For CABG x3, bill 33533 x3, not once.
Link ICD-10 Codes – Example: I25.10 (atherosclerotic heart disease), I20.0 (unstable angina).
Pre-Submission Audits – Use tools like AAPC’s Code Explorer to catch unbundling errors.

Case Study: A Texas hospital reduced CABG claim denials by 40% after training coders to annotate vein harvest methods (endoscopic vs. open).

Reimbursement Insights for CPT Code 33533

Average Payment (2024–2025): $2,300 – $2,800 (varies by payer).
Category II Codes (e.g., 3353F): Useful for performance tracking but don’t affect reimbursement.
Denial Triggers: Unbundled claims, missing modifiers, incorrect unit counts.

Conclusion

CPT code 33533 is the go-to code for CABG using venous grafts only, but billing errors are common. By understanding neighboring CABG codes, applying modifiers correctly, and documenting graft types, providers and billing specialists can reduce denials and accelerate reimbursements.

If you’re struggling with complex CABG claims, consult with a cardiac billing expert. Even small improvements in coding accuracy can prevent weeks of lost revenue.