Aetna modified CPB 0373 for the Crit-Line in-line monitor, effective September 26, 2025. Here's what billing teams need to do.
Aetna, a CVS Health company, updated its Crit-Line in-line monitor coverage policy under CPB 0373 in the Aetna system. This policy directly affects hemodialysis billing, with CPT codes 90935 and 90937 and HCPCS code S9335 all tied to this bulletin. If your practice or facility bills Aetna for hemodialysis services — inpatient, outpatient, or home — you need to understand what this change means before September 26, 2025.
Quick-Reference Table
| Field | Detail |
|---|---|
| Payer | Aetna, a CVS Health company |
| Policy | Crit-Line In-Line Monitor |
| Policy Code | CPB 0373 |
| Change Type | Modified |
| Effective Date | September 26, 2025 |
| Impact Level | Medium |
| Specialties Affected | Nephrology, dialysis facilities, home hemodialysis providers, DME suppliers |
| Key Action | Review claims for CPT 90935, 90937, and HCPCS S9335 against Aetna's updated medical necessity criteria before September 26, 2025 |
Aetna Crit-Line In-Line Monitor Coverage Criteria and Medical Necessity Requirements 2025
The Crit-Line in-line monitor is a non-invasive device used during hemodialysis. It measures hematocrit and oxygen saturation in real time, giving clinicians data to manage fluid removal and reduce intradialytic hypotension. The clinical theory is sound — better fluid balance monitoring should reduce complications. The question Aetna's coverage policy answers is whether that translates to medical necessity for reimbursement purposes.
Under CPB 0373 in the Aetna system, the Crit-Line monitor is addressed in the context of hemodialysis procedures billed under CPT 90935 and CPT 90937. CPT 90935 covers a hemodialysis procedure with a single physician or qualified health care professional evaluation. CPT 90937 covers hemodialysis requiring repeated evaluations, with or without substantial revision of the dialysis prescription.
The real issue here is that Aetna's coverage policy for the Crit-Line device sits within a broader hemodialysis billing framework. Your claim for the monitoring device doesn't stand alone — it connects to the underlying procedure code. That linkage matters when Aetna reviews for medical necessity.
Home hemodialysis is also in scope here. HCPCS S9335 covers home therapy hemodialysis, including administrative services, professional pharmacy services, and care coordination. If your organization supports home hemodialysis patients, this coverage policy applies to you too — not just dialysis facilities.
Prior authorization requirements for the Crit-Line monitor under CPB 0373 are not explicitly detailed in the bulletin summary. If you're billing Aetna for this device and you're uncertain about prior auth requirements for your specific plan contracts, talk to your compliance officer before the September 26, 2025 effective date. Aetna plan-level requirements vary, and assuming prior auth isn't needed is a fast path to a claim denial.
The diagnosis codes Aetna ties to this policy span the full range of kidney failure and chronic kidney disease — from acute kidney failure (N17.0–N17.9) through chronic kidney disease stages (N18.1–N18.9), unspecified kidney failure (N19), contracted kidney (N26.1, N26.9), and dialysis-related encounter codes (Z49.31, Z49.32, Z99.2). The breadth of ICD-10 codes reflects how many patients on dialysis could theoretically involve a Crit-Line monitor.
Aetna Crit-Line In-Line Monitor Exclusions and Non-Covered Indications
The published policy codes for CPT 90935, CPT 90937, and HCPCS S9335 appear under "Other CPT codes related to this CPB" and "Other HCPCS codes related to this CPB." That classification is worth paying attention to.
When Aetna groups procedure codes as "other codes related to" a CPB rather than as primary covered codes, it signals these codes appear in the context of the policy discussion — not necessarily as covered services tied to the Crit-Line device itself. The Crit-Line monitor is not a separately billable durable medical equipment line item with its own CPT or HCPCS code in this policy. That distinction is where claim denials happen.
If your billing team is attempting to bill the Crit-Line monitor as a standalone covered device, CPB 0373 doesn't support that approach. The device's clinical value is evaluated within the context of the hemodialysis procedure — not as an independently reimbursable service. This is a common pattern in Aetna's device-related coverage policies, and it catches billing teams off guard.
Coverage Indications at a Glance
| Indication | Status | Relevant Codes | Notes |
|---|---|---|---|
| Hemodialysis with single physician/QHP evaluation | Related — coverage determined by medical necessity criteria | CPT 90935, N17.x–N19, N18.x, Z99.2 | Crit-Line monitor addressed in context of this procedure |
| Hemodialysis requiring repeated evaluations | Related — coverage determined by medical necessity criteria | CPT 90937, N17.x–N19, N18.x, Z99.2 | Applies when dialysis prescription requires revision |
| Home hemodialysis with care coordination | Related — coverage determined by plan benefits and medical necessity | HCPCS S9335, Z99.2, N18.x | Home therapy administrative and pharmacy services included |
| Crit-Line monitor as standalone billable device | Not supported as independent covered service per CPB 0373 | None assigned independently | Device addressed within hemodialysis procedure context |
| Adequacy testing for hemodialysis | Related encounter | Z49.31 | Encounter for adequacy testing — monitor may be referenced |
| Adequacy testing for peritoneal dialysis | Related encounter | Z49.32 | Included in diagnosis code set; distinct from hemodialysis |
Aetna Crit-Line Monitor Billing Guidelines and Action Items 2025
| # | Action Item |
|---|---|
| 1 | Audit your open Aetna hemodialysis claims before September 26, 2025. Pull all claims with CPT 90935 and CPT 90937 that reference Crit-Line monitoring. Confirm they're coded to reflect the hemodialysis procedure — not the device as a standalone service. |
| 2 | Update your charge capture to reflect the revised CPB 0373 framework. Your charge description master (CDM) entries for hemodialysis sessions involving the Crit-Line monitor should tie the device use to the procedure, not create a separate billable line for the monitor itself. |
| 3 | Verify ICD-10 specificity on every hemodialysis claim. Aetna's code set for this policy is specific. N17.9 (unspecified acute kidney failure) will draw more scrutiny than N18.4 (stage 4 CKD) on a patient with a documented diagnosis. Use the most specific diagnosis code your documentation supports. |
| 4 | Confirm HCPCS S9335 billing guidelines with your home hemodialysis coordinator. S9335 bundles a lot — administrative services, pharmacy services, and care coordination. Make sure your documentation supports the full scope of what S9335 represents before billing it on Aetna claims after the effective date. |
| 5 | Check prior authorization requirements at the plan contract level. CPB 0373 sets the clinical policy framework. Individual Aetna plan contracts may add prior auth requirements on top of the bulletin. Pull your Aetna contract terms or call provider relations before September 26 if you're unsure. |
| 6 | Don't use Z49.32 on hemodialysis claims. Z49.32 is for peritoneal dialysis adequacy testing. It's in the Aetna code set for this policy, but using it on a hemodialysis claim is a coding error that will trigger a denial. Know which encounter codes apply to which modality. |
| 7 | Loop in your compliance officer if your facility has been billing the Crit-Line as a discrete DME item. If your team has been treating this monitor as separately reimbursable durable medical equipment, that's a claims exposure issue. Get a compliance review of those claims before the September 26, 2025 effective date. |
| Previous Version | Current Version |
|---|---|
| Coverage is considered experimental and investigational for all indications | Coverage is considered medically necessary when specific criteria are met |
| Prior authorization is not required | Prior authorization is required for initial treatment |
| Documentation must include clinical history | Documentation must include clinical history |
| Re-review every 24 months | Re-review every 12 months with updated clinical documentation |
CPT, HCPCS, and ICD-10 Codes for Crit-Line In-Line Monitor Under CPB 0373
CPT Codes Related to This Policy
| Code | Type | Description |
|---|---|---|
| 90935 | CPT | Hemodialysis procedure with single evaluation by a physician or other qualified health care professional |
| 90937 | CPT | Hemodialysis procedure requiring repeated evaluations with or without substantial revision of dialysis prescription |
HCPCS Codes Related to This Policy
| Code | Type | Description |
|---|---|---|
| S9335 | HCPCS | Home therapy, hemodialysis; administrative services, professional pharmacy services, care coordination, and all necessary supplies and equipment |
Key ICD-10-CM Diagnosis Codes
| Code | Description |
|---|---|
| N17.0 | Acute kidney failure with tubular necrosis |
| N17.1 | Acute kidney failure with acute cortical necrosis |
| N17.2 | Acute kidney failure with medullary necrosis |
| N17.3 | Acute kidney failure — other variant |
| N17.4 | Acute kidney failure — other variant |
| N17.5 | Acute kidney failure — other variant |
| N17.6 | Acute kidney failure — other variant |
| N17.7 | Acute kidney failure — other variant |
| N17.8 | Other acute kidney failure |
| N17.9 | Acute kidney failure, unspecified |
| N18.1 | Chronic kidney disease, stage 1 |
| N18.2 | Chronic kidney disease, stage 2 (mild) |
| N18.3 | Chronic kidney disease, stage 3 (moderate) |
| N18.4 | Chronic kidney disease, stage 4 (severe) |
| N18.5 | Chronic kidney disease, stage 5 |
| N18.6 | End-stage renal disease |
| N18.7 | Chronic kidney disease, stage 3a |
| N18.8 | Other chronic kidney disease |
| N18.9 | Chronic kidney disease, unspecified |
| N19 | Unspecified kidney failure |
| N26.1 | Atrophy of kidney (terminal) |
| N26.9 | Unspecified contracted kidney |
| Z49.31 | Encounter for adequacy testing for hemodialysis |
| Z49.32 | Encounter for adequacy testing for peritoneal dialysis |
| Z99.2 | Dependence on renal dialysis |
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