CPT® Code 93971

Quick Reference

• Code definition: CPT 93971 reports a duplex scan of extremity veins (B-mode imaging plus Doppler) for either one extremity examined completely (unilateral) or a study that does not cover all major venous segments of both extremities (limited).
• Key billing rule: MUE = 1 unit per date of service. A single unit covers the full unilateral or limited study regardless of how many segments are imaged within the scope of a limited examination [4].
• Modifier essentials: Append -RT or -LT to specify laterality; many MACs require this for claims processing. In hospital outpatient and IDTF settings, the facility bills -TC and the interpreting physician bills -26 on separate claims [1].
• Documentation must-have: The report must name each venous segment examined and document compressibility findings and Doppler waveform characteristics per segment. A report stating only "no DVT" without listing imaged segments does not support the code.
• Top confusion point: Using 93970 when only one extremity was examined is the most frequent error for this code family. If the study report covers one limb, 93971 is correct regardless of the clinical intent [1].
• Payer alert: The bilateral surgery indicator is 0, meaning the 150% bilateral payment adjustment does not apply to 93971. Billing 93971-RT and 93971-LT on the same date may conflict with the MUE of 1; verify MAC-specific policy before submitting both units [5].
• PC/TC split: PC/TC indicator = 1 (Diagnostic Tests for Radiology Services). This code is subject to TC multiple procedure reduction (indicator 6): when multiple diagnostic cardiovascular ultrasound TCs are billed on the same date, the highest-valued TC pays at 100% and subsequent TCs reduce to 75% [5].

When to Use This Code

Clinical indications driving 93971 include any scenario where venous evaluation of an extremity is clinically warranted but the scope does not constitute a complete bilateral study. The ACR Appropriateness Criteria (2023) rates duplex ultrasound as "Usually Appropriate" as the first-line modality for suspected lower-extremity DVT [7]. Common clinical triggers:

• Unilateral leg or arm swelling with suspected acute DVT (calf, proximal lower extremity, or upper extremity)
• Source workup for pulmonary embolism
• Surveillance of known or treated DVT in a single limb
• Pre-ablation venous mapping of one leg (saphenous vein, perforators)
• Catheter-associated or PICC-line thrombosis (upper extremity, typically unilateral)
• Chronic venous insufficiency evaluation in one limb
• Post-thrombotic syndrome follow-up, single extremity
• Proximal-only follow-up imaging when tibial evaluation is deferred (limited study)

Scope boundaries define both uses of the code. "Unilateral" means a complete evaluation of one limb: all relevant venous segments for that extremity type (e.g., CFV, femoral, popliteal, GSV, tibials for a complete lower extremity study). "Limited" means the examination did not encompass the full venous anatomy, regardless of whether one or both extremities were partially imaged. Evaluating only the proximal system (femoral and popliteal) without the tibials, or imaging only the superficial system (GSV) without the deep system, both qualify as limited studies [1].

Provider and setting context: 93971 is billed across radiology, vascular surgery, cardiology, and vascular lab (IDTF) settings. The code is a diagnostic imaging service (PC/TC = 1), so the professional and technical components are separately billable when performed in a split-bill environment. In a physician office that owns the equipment, the global code (no modifier) is billed. In a hospital outpatient department, the facility claims -TC and the interpreting physician claims -26 separately [5].

Code Differentiation Table

The critical differentiator is completeness, not laterality. If both legs were scanned but only the proximal segments were imaged, 93971 (limited) is correct. 93970 requires documentation of every major venous segment in both limbs. Auditors flag 93970 claims that lack bilateral segment-by-segment findings, and those claims are vulnerable to downcoding to 93971.

flowchart TD
    A[Extremity venous duplex performed] --> B{Both extremities\nimaged?}
    B -- No --> C[93971\nUnilateral]
    B -- Yes --> D{All major segments\ncomplete on both sides?}
    D -- No --> E[93971\nLimited]
    D -- Yes --> F[93970\nComplete bilateral]

Billing & Modifier Rules

Modifier usage:

• -26 / -TC: Required in any split-bill environment. Interpreting physician appends -26; facility or IDTF appends -TC. Never bill the global code from two separate entities; that constitutes duplicate billing [5].
• -RT / -LT: Required by many MACs and commercial payers to identify laterality. Omitting laterality modifiers on 93971 claims is a common rejection trigger. The CPT descriptor does not mandate them, but payer policy does.
• -76 (Repeat Procedure, Same Provider): Appropriate only when a second medically necessary study is performed on the same day by the same provider with documented distinct clinical indication.
• -52 (Reduced Services): Do not use to denote a unilateral study. 93971 already captures unilateral scope by descriptor. Using -52 on top of 93971 would imply a service less complete than a standard limited study and would further reduce payment without clinical justification.
• -59 / -XS (Separate Structure): May be needed when billing extremity venous duplex alongside extremity arterial duplex (e.g., 93971 + 93925) on the same date, to indicate the arterial and venous systems are distinct anatomic structures [3].

MUE and units: The CMS MUE for 93971 is 1 unit per date of service [4]. Attempting to bill 93971-RT and 93971-LT on the same date for bilateral limited studies may conflict with this MUE. Some MACs permit bilateral limited reporting with laterality modifiers; verify MAC-specific policy before submitting dual units. When in doubt, query the MAC or escalate to the compliance team.

Multiple procedure reduction (TC): When 93971 is billed with other diagnostic cardiovascular ultrasound services on the same date, the TC of the lower-valued service reduces to 75% of the fee schedule. The professional component (-26) is not subject to this reduction [5].

Global period: Global days = XXX (concept does not apply). Each study is billed independently with no pre- or post-operative follow-up period included in the payment [5].

Documentation Essentials

Required elements for a compliant 93971 report:

1. Clinical indication or ordering diagnosis (supports medical necessity)
2. Identified extremity (right, left, upper, lower) and specific venous segments evaluated by name (CFV, femoral, popliteal, GSV, anterior tibial, posterior tibial, peroneal, etc. as appropriate)
3. Compressibility findings per segment: fully compressible, partially compressible, or non-compressible
4. Doppler waveform characteristics: spontaneous flow, phasic variation, augmentation response to distal compression
5. Presence or absence of intraluminal echogenicity (thrombus); if present, echogenicity (acute vs chronic) and extent
6. Results of compression maneuvers or other provocative testing performed
7. Permanent images archived for each evaluated segment
8. Signed final report with clinical interpretation, impressions, and recommendations

Audit red flags specific to this code:

• Report documents only bilateral findings but claim is billed as 93970; auditors expect 93971 when documentation does not confirm all bilateral segments were imaged
• Templated reports where segment-level findings are not individualized (e.g., all segments marked "compressible, no DVT" without specifics)
• No documentation of the Doppler component; B-mode alone does not constitute a duplex scan
• Compression maneuvers referenced in the descriptor are absent from the report
• Study ordered without documented clinical indication; asymptomatic surveillance without documented risk factors fails medical necessity under LCD criteria [2]

Medical necessity: MAC LCDs for noninvasive vascular studies (e.g., Novitas LCD L33619 and equivalents) specify covered indications including acute DVT signs or symptoms, PE source workup, known DVT follow-up with documented clinical change, chronic venous insufficiency with objective findings, pre-procedural venous mapping, and catheter-associated thrombosis [2]. The diagnosis code submitted must reflect the clinical indication at the time of the order, not a confirmed DVT that had not yet been diagnosed when the study was ordered. For suspected DVT workups, a symptom code (e.g., R60.0 for localized edema) is appropriate until results confirm the diagnosis.

Medicare, Commercial & Medicaid Payer Rules

Medicare:

Multiple MACs maintain LCDs covering CPT 93971 under noninvasive vascular diagnostic studies policies [2]. Coverage is available for the clinical indications listed in the Documentation Essentials section. Routine or screening studies in asymptomatic patients without documented risk factors are not covered. Repeat studies require documented interval clinical change or a new clinical indication.

The 2025 Physician Fee Schedule conversion factor was $32.3465 before locality adjustment and legislative modification [6]. RVUs differ between facility (lower) and non-facility (higher) settings, reflecting the cost of equipment in a non-facility environment. Confirm current RVU values against the CMS PFS lookup tool.

93971 is not subject to a surgical global period (XXX indicator), is not payable in an ASC setting for diagnostic imaging (verify MAC policy), and the technical component is subject to the code 6 multiple procedure reduction when multiple cardiovascular diagnostic ultrasound TCs are billed on the same date [5].

Commercial payers:

Commercial policies generally follow Medicare coverage rationale for 93971 but may impose prior authorization requirements for non-emergency venous duplex, particularly for pre-procedural venous mapping and surveillance studies. Some payers require specific ICD-10-CM codes to appear on the claim (rather than symptom codes) to generate automatic coverage determination. Verify payer-specific diagnosis code lists before submitting claims for chronic venous insufficiency or varicose vein indications.

Common Denials & Prevention

Upcoding denial: 93970 billed, 93971 payable The payer or MAC downcodes 93970 to 93971 when the clinical documentation does not support a complete bilateral study. This occurs when the report lacks bilateral segment documentation or when only one extremity was examined. Prevention: Code from the report, not the order. If the report documents one extremity, bill 93971 regardless of what was ordered.

Missing laterality modifier Claims submitted without -RT or -LT are rejected by MACs and commercial payers that require laterality identification on unilateral services. Prevention: Establish a billing workflow that requires laterality modifiers on all 93971 claims; treat the absence of a modifier as an edit that must be resolved before submission.

Medical necessity denial: insufficient clinical indication Payers deny claims when the submitted diagnosis code does not map to a covered indication in the applicable LCD, or when the diagnosis code selected does not reflect the documented clinical scenario (e.g., a confirmed DVT code submitted for a rule-out study, which may flag as retrospective diagnosis assignment). Prevention: Confirm that the ICD-10-CM code on the claim matches the indication documented at the time of the order. For suspected DVT, use symptom codes at ordering and update to confirmed diagnosis codes after results are available.

Bundling denial: 93971 billed with 93970 same date 93971 is a component of 93970; billing both codes for the same extremity type on the same date is an unbundling error [3]. Prevention: If a complete bilateral study was performed, bill 93970 only. Code 93971 is redundant and will be denied.

MUE denial: second unit on same date Submitting 93971-RT and 93971-LT on the same date may exceed the MUE of 1 unit [4]. Prevention: Verify MAC policy on bilateral limited studies reported with laterality modifiers before submitting dual units. Some MACs permit this; others do not. If denied, appeal with clinical documentation supporting the distinct clinical necessity for each limb evaluation.

Coding Scenarios

Scenario 1: A 58-year-old woman with a recent hip replacement presents with left leg swelling and calf tenderness. The vascular lab performs a duplex scan of the left lower extremity, evaluating the common femoral, femoral, popliteal, and tibial veins with compression responses. The right leg is not examined.

Correct coding: 93971-LT + R60.0 (localized edema) at ordering; update to I82.402 (acute DVT, left lower extremity) once DVT is confirmed on the report.

Why: One extremity was fully examined. 93971 is the unilateral study code. 93970 is incorrect because the bilateral study was not performed.

Scenario 2: A patient with bilateral lower extremity DVT diagnosed three months prior returns for follow-up. Due to time constraints, the sonographer images only the bilateral femoral and popliteal veins; tibial veins are not evaluated on either side. The report documents proximal bilateral findings only.

Correct coding: 93971 (no laterality modifier, as both sides were partially imaged but study is limited) + I82.4Y3 (chronic DVT, proximal lower extremity, bilateral) or the appropriate chronic/acute equivalent.

Why: Both extremities were imaged but the study was limited to proximal segments. The examination was not complete on either side, making 93971 (limited) the correct code. 93970 requires all major venous segments on both sides.

Scenario 3: A hospital outpatient department performs a right lower extremity venous duplex for suspected DVT. The hospital employs a vascular sonographer who performs the scan; a radiologist from an independent radiology group interprets and signs the report.

Correct coding: Hospital submits 93971-TC-RT on the facility UB-04. Radiologist submits 93971-26-RT on the CMS-1500 professional claim.

Why: PC/TC indicator 1 permits component billing. Each entity bills only its component; neither bills the global code, which would duplicate payment.

Scenario 4: A patient with a PICC line in the right arm develops right arm swelling. A duplex scan evaluates the right basilic, brachial, axillary, and subclavian veins. Thrombus is identified in the right axillary vein.

Correct coding: 93971-RT + I82.A11 (acute embolism and thrombosis of right axillary vein).

Why: Upper extremity venous duplex falls within 93971 just as lower extremity studies do. The code is not limited to the lower extremity; laterality modifier -RT specifies the examined limb.

Related Codes

• 93970 — Duplex scan of extremity veins; complete bilateral study. Bilateral counterpart; use when all major venous segments of both limbs are fully documented.
• 93978 — Duplex scan of aorta, IVC, iliac vasculature; complete study. May be ordered alongside 93971 when central venous obstruction is suspected.
• 93979 — Duplex scan of aorta, IVC, iliac vasculature; unilateral or limited study. Limited iliac or IVC evaluation paired with extremity venous duplex.
• 93925 — Duplex scan of lower extremity arteries; complete bilateral study. Arterial counterpart; separately reportable when arterial and venous systems are independently evaluated.
• 93926 — Duplex scan of lower extremity arteries; unilateral or limited study. Unilateral arterial lower extremity duplex; may be paired with 93971 with appropriate modifier.
• 93930 — Duplex scan of upper extremity arteries; complete bilateral study. Upper extremity arterial counterpart.
• 93931 — Duplex scan of upper extremity arteries; unilateral or limited study. Upper extremity arterial unilateral or limited counterpart.
• 93990 — Duplex scan of hemodialysis access. Post-creation AV access surveillance; distinct from native extremity venous evaluation.

Sources

1. AMA CPT 2025 Professional Edition — Official CPT code descriptor and coding guidelines for 93970 and 93971.
2. CMS Medicare Coverage Database — MAC LCDs for noninvasive vascular diagnostic studies; Novitas LCD L33619 and equivalents.
3. CMS NCCI Policy Manual Chapter 9 — Bundling rules for vascular diagnostic ultrasound codes including 93970 and 93971.
4. CMS NCCI MUE Tables — Practitioner Services — MUE of 1 unit per date of service for CPT 93971.
5. CMS Physician Fee Schedule 2025 Final Rule — RVU values, PC/TC indicator, global days, bilateral indicator, multiple procedure indicator for 93971.
6. Federal Register Vol. 89 — CY 2025 MPFS Final Rule — Annual MPFS rule for 2025 payment policies including conversion factor.
7. ACR Appropriateness Criteria — Suspected Lower-Extremity DVT — Clinical guideline supporting duplex ultrasound as first-line modality for suspected DVT (updated 2023).