As ICD-10 denial trends continue to reveal insights into documentation trends, payer expectations, and compliance challenges as the healthcare industry moves deeper into 2025. The first quarter of the year (Q1 2025) brought a mix of the expected and the surprising in terms of ICD-10-CM diagnosis code denials. This newsletter provides an in-depth analysis of the most frequently denied ICD-10-CM codes, explores the root causes behind these denials, and offers guidance to healthcare organizations on how to mitigate risks and improve reimbursement.
Understanding the Landscape: Why Denials Occur
Diagnosis code denials can occur for a variety of reasons, including insufficient documentation, coding to an unspecified level, medical necessity conflicts, and mismatches between diagnosis and procedure codes. As ICD-10 denial trends indicate a growing scrutiny of diagnostic coding, particularly with payers increasing their reliance on algorithms and AI for claim adjudication, the specificity and accuracy of ICD-10-CM coding have never been more critical.
Top 10 Most Frequently Denied ICD-10-CM Codes in Q1 2025
Based on aggregated data from hospitals, outpatient clinics, and physician practices across the U.S., the following codes topped the list of denials in the first quarter of 2025:
1. R10.9 – Unspecified Abdominal Pain
2. M54.5 – Low Back Pain
3. R07.9 – Chest Pain, Unspecified
4. J06.9 – Acute Upper Respiratory Infection, Unspecified
5. E11.9 – Type 2 Diabetes Mellitus without Complications
6. F41.9 – Anxiety Disorder, Unspecified
7. I10 – Essential (Primary) Hypertension
8. R51.9 – Headache, Unspecified
9. N39.0 – Urinary Tract Infection, Site Not Specified
10. R53.1 – Weakness
Let’s break down each code and uncover the common pitfalls leading to denials.
1. R10.9 – Unspecified Abdominal Pain
Why it’s denied:
- Lack of specificity (e.g., location, duration, underlying cause)
- Overuse in initial encounters without proper follow-up
- Medical necessity not clearly established in documentation
Tip for providers: Utilize more specific codes like R10.11 (Right upper quadrant pain) or R10.32 (Left lower quadrant pain) when appropriate. Ensure diagnostic tests are referenced to support the clinical findings.
2. M54.5 – Low Back Pain
Why it’s denied:
- Considered a symptom code, not a standalone diagnosis
- Often flagged for medical necessity issues, especially with imaging or PT services
Tip for providers: Document any underlying condition such as lumbar disc displacement or spinal stenosis. Pair with treatment plans or diagnostic imaging results to establish medical necessity.
3. R07.9 – Chest Pain, Unspecified
Why it’s denied:
- Overused in emergency departments without follow-up diagnosis
- Vague documentation that doesn’t rule out serious conditions
Tip for providers: When ruling out cardiac events, specify findings such as angina (I20.9) or costochondritis (M94.0). Link symptoms to diagnostic workup outcomes.
4. J06.9 – Acute Upper Respiratory Infection, Unspecified
Why it’s denied:
- High audit risk due to overlap with COVID-19 or influenza
- Lack of documentation about symptom onset and clinical findings
Tip for providers: Use specific codes like J02.9 (acute pharyngitis), J01.90 (acute sinusitis), or J20.9 (acute bronchitis) when able. Always note patient history and potential exposure risks.
5. E11.9 – Type 2 Diabetes Mellitus without Complications
Why it’s denied:
- Incomplete documentation of diabetic control and complications
- Frequent mismatch with procedures requiring more severe diagnoses
Tip for providers: Document whether the patient has complications such as neuropathy (E11.40) or retinopathy (E11.319). Include current A1c levels and medication adherence in notes.
6. F41.9 – Anxiety Disorder, Unspecified
Why it’s denied:
- Insufficient behavioral health documentation
- Lack of specificity and treatment plan
Tip for providers: Use specific codes like F41.1 (generalized anxiety disorder) or F40.10 (social phobia). Include assessment tools, treatment plans, and follow-up schedules.
7. I10 – Essential (Primary) Hypertension
Why it’s denied:
- Payer scrutiny when used as a primary diagnosis for certain visits
- Documentation often fails to indicate severity or impact on other conditions
Tip for providers: If hypertension is contributing to heart or kidney conditions, use combination codes (e.g., I13.0 for hypertensive heart and kidney disease). Ensure vitals and related assessments are included in documentation.
8. R51.9 – Headache, Unspecified
Why it’s denied:
- Flagged for medical necessity, especially for advanced imaging
- Lack of differentiation between migraine, tension, or cluster headaches
Tip for providers: When the headache is recurring or severe, use more descriptive codes like G43.909 (migraine, unspecified, not intractable) or G44.1 (vascular headache). Tie symptoms to clinical assessments.
9. N39.0 – Urinary Tract Infection, Site Not Specified
Why it’s denied:
- Incomplete urinalysis or culture documentation
- Used without evidence of infection or treatment plan
Tip for providers: Reference lab results and specify site if known (e.g., N30.00 for acute cystitis). Include antibiotic prescription and follow-up in patient record.
10. R53.1 – Weakness
Why it’s denied:
- Considered a symptom, not a definitive diagnosis
- High scrutiny when billed alongside complex services
Tip for providers: Clarify whether the weakness is due to a neurological, metabolic, or musculoskeletal condition. When applicable, use specific codes like G72.89 (other specified myopathies) or M62.81 (muscle weakness/generalized).
Trends & Takeaways
Several themes emerged from Q1 2025 denials:
- Unspecified codes are under fire. Payers increasingly deny claims with generic or vague codes, especially when more detailed options exist.
- Symptom codes require context. R codes (e.g., R10.9, R07.9) must be supported with robust documentation or tied to definitive diagnoses.
- Behavioral health remains challenging. Mental health diagnoses need to be accompanied by specific, ongoing treatment documentation.
- Chronic condition management is key. Chronic diseases like diabetes and hypertension require not just identification but evidence of assessment, control, and impact.
- Diagnostic specificity supports reimbursement. When clinicians can link symptoms to conditions and show a plan of care, denial risks are greatly reduced.
Proactive Strategies to Reduce Denials
To improve claim acceptance and reduce the administrative burden of appeals, consider these best practices:
- Invest in clinical documentation improvement (CDI) training: Ensure providers understand how to document with payer expectations in mind.
- Implement pre-submission claim audits: Use automated tools or manual reviews to catch vague or high-risk codes.
- Engage coders in education loops: Coders should work closely with clinical teams to flag frequent denial triggers and share corrective feedback.
- Use decision-support tools: Real-time coding suggestions embedded in EHRs can help clinicians select the most appropriate ICD-10-CM codes.
- Track denial trends: Monitor monthly denial reports to identify persistent problem areas.