CPT Code 85300Complete Billing & Coding Guide (2026)Antithrombin iii activity
About CPT 85300
CPT 85300 is a Current Procedural Terminology code in the Pathology/Lab category maintained by the American Medical Association. The CMS short descriptor reads "Antithrombin iii activity". For the full AMA long descriptor and clinical guidance, refer to the current CPT code manual.
Documentation specificity, correct ICD-10 linkage, and modifier accuracy determine whether 85300 pays cleanly or triggers a denial. Verify CMS National Physician Fee Schedule status, applicable Medicare LCDs, and any payer-specific medical policies before submission.
85300 has 5 NCCI bundling edit pairs documented. Run your scrubber against the NCCI quarterly update before submission. When clinically warranted, use modifier 59 or the X-modifiers (XE, XS, XP, XU) to bypass an indicator-1 edit, with chart documentation supporting the distinct service.
Code Properties
RVU Breakdown
Every CPT code’s Medicare payment is calculated from three Relative Value Unit components: physician work, practice expense, and malpractice. Together they multiply by the conversion factor to produce the payment amount.
Payment = Total RVU × Conversion Factor ($33.4009) × Geographic Adjustment (GPCI). National averages shown. Actual payment varies by locality.
NCCI Bundling Edits
5 pairsThese codes trigger National Correct Coding Initiative edits when billed with 85300. An indicator of 0 means the pair cannot be unbundled. Indicator 1 means modifier 59 or X-modifiers may allow separate billing with supporting documentation.
85300 + 80503: bundled, modifier may bypass (indicator 1)
The most-asked bundling question on this code. Verdict pulled from the current NCCI quarterly file.
Modifier indicator 1 means a modifier may bypass the edit when the clinical scenario supports a distinct, separately identifiable service. Most billers default to modifier 59, but payers prefer the more specific X-modifiers (XE, XS, XP, XU) and pay them with less audit scrutiny. Documentation must establish the separation factor.
Standards of medical/surgical practice
Billing 85300 alongside a bundled code without the correct modifier generates CARC 97 denials. Payers often flag these as audit risks. Document medical necessity for the separate service and apply modifier 59 or the appropriate X-modifier (XE, XS, XP, XU) only when clinically justified.
Standards of medical/surgical practice
Standards of medical/surgical practice
Standards of medical/surgical practice
Standards of medical/surgical practice
CPT Manual or CMS manual coding instruction
Bundling denials on 85300 are recoverable when the edit indicator is 1 and the chart documents a distinct, separately identifiable service. Our coders verify the indicator and pick the precise X-modifier (XE, XS, XP, XU) instead of defaulting to modifier 59.
Denied on 85300 + 80503 with the wrong modifier? Send us the EOB.
Most bundling denials on 85300 are recoverable when an X-modifier replaces a generic mod 59 and the chart supports a distinct service. A coder will read the EOB and the operative or procedure note for you.
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Applicable Modifiers
Modifiers commonly paired with 85300 based on its category. Apply only when the clinical circumstance warrants. Incorrect modifier use is a top audit target.
Component split modifiers (26 professional, TC technical) are the most under-applied modifiers in diagnostic billing. Practices that bill global on services where they only provided the read silently invite refund requests. We split components correctly at submission.
Find the revenue leakage in your 85300 claims.
Wrong modifier, missing documentation, bundling without justification, stale ICD-10 linkage: these are the silent revenue killers on Pathology/Lab claims. Our AAPC-certified team audits your last 90 days of 85300 claims, surfaces the recoverable dollars, and appeals them. Free, no obligation.
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Related CPT Codes
Codes in the same family as 85300
Everything about CPT 85300
What does CPT code 85300 cover?
CPT 85300 is a Current Procedural Terminology code in the Pathology/Lab category maintained by the American Medical Association. The CMS short descriptor reads "Antithrombin iii activity". For the full AMA long descriptor and clinical guidance, refer to the current CPT code manual.
What is the Medicare payment for CPT 85300?
The national average Medicare payment for CPT 85300 is approximately $0 in a non-facility setting and $0 in a facility setting. Actual payment varies by locality based on GPCI adjustments. Total RVU is 0 with a conversion factor of $33.4009.
What is the global period for CPT 85300?
CPT 85300 has no global period (indicator XXX). There are no post-operative day restrictions tied to this code. Refer to CMS National Physician Fee Schedule rules and any applicable NCCI edits when billing on the same date as other services.
What codes bundle with CPT 85300?
CPT 85300 has NCCI Procedure-to-Procedure edits with 5+ codes including 80503, 80504, 80505. Modifier indicator 0 means the edit cannot be bypassed. Indicator 1 means modifier 59 or X-modifiers may allow separate billing with documentation.
CPT codes and descriptions are copyright of the American Medical Association. RVU values reflect current CMS publications. Actual payment varies by locality. Commercial payer rates vary by contract.
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We audit your last 90 days of claims and surface the revenue leakage: wrong modifiers, missed bundling appeals, ICD-10 specificity gaps. AAPC-certified coders. 2.49% of collections. No setup fees.