Flank pain, the discomfort felt in the side of the torso between the ribs and the hip, is one of the most frequent presenting complaints in primary care, urgent care, and emergency departments. For years, coders had no flank specific option and defaulted to R10.9 (unspecified abdominal pain) or nearby quadrant codes. That changed on October 1, 2025, when ICD-10-CM introduced a dedicated flank pain code family for the first time.
If you are searching for the correct ICD-10 code for flank pain, the ICD-10 code for right flank pain, or simply trying to confirm whether R10.9 is still acceptable, this guide covers the complete FY2026 code set, how each code is used, and how to avoid the documentation gaps that trigger claim denials. ProMantra’s medical coding team put this guide together to help practices and billing staff transition smoothly to the updated code set.
What Is Flank Pain, Clinically Speaking?
Flank pain refers to pain in the lateral (side) region of the trunk, roughly between the lowest rib and the top of the hip bone, often extending toward the back. It is distinct from anterior abdominal pain and from lower back pain at the midline spine. Because flank pain can point to anything from a benign muscle strain to an obstructing renal calculus, ICD-10-CM specificity matters for both medical necessity and for guiding the clinical workup that follows.
Clinically, flank pain is most often associated with:
- Renal colic and kidney stones, causing sharp pain that often radiates to the groin
- Pyelonephritis or urinary tract infection, accompanied by fever, dysuria, or costovertebral angle (CVA) tenderness
- Musculoskeletal strain, producing dull, positional pain that worsens with movement
ICD-10 Code for Flank Pain: The New 2026 Code Family (R10.A0 to R10.A3)
The most significant coding update affecting this complaint is the addition of category R10.A, Pain localized to flank, effective with the FY2026 ICD-10-CM release on October 1, 2025. R10.A itself is a non-billable parent code, so claims must use one of its four billable subcodes shown below.
ICD-10-CM Code | Description | Status |
|---|---|---|
R10.A0 | Flank pain, unspecified side | New, billable, effective 10/1/2025 |
R10.A1 | Flank pain, right side | New, billable, effective 10/1/2025 |
R10.A2 | Flank pain, left side | New, billable, effective 10/1/2025 |
R10.A3 | Flank pain, bilateral | New, billable, effective 10/1/2025 |
Before this update, anyone searching for the icd 10 flank pain code would typically land on R10.9 or an adjacent abdominal quadrant code, since neither option actually represented the flank as a documented anatomical site. The R10.A family closes that gap entirely and gives coders a code that matches provider documentation word for word when the note reads right flank pain or left flank pain.
ICD-10 Code for Right Flank Pain (R10.A1)
R10.A1, Flank pain, right side, is the code to use whenever documentation specifies right sided flank pain without a confirmed underlying diagnosis. This is now the direct answer to the question: what is the icd 10 code for right flank pain for any FY2026 date of service.
Right flank pain is frequently linked to:
- A right sided ureteral or renal calculus (kidney stone)
- Right pyelonephritis or upper urinary tract infection
- Musculoskeletal strain along the right paraspinal or intercostal region
R10.A1 is appropriate when flank pain is the reason for the encounter and no cause has yet been established. Once a definitive diagnosis is confirmed, ICD-10-CM guidelines require coding that diagnosis rather than the symptom code.
Left, Bilateral, and Unspecified Flank Pain Codes
R10.A2, Flank pain, left side, mirrors R10.A1 for the opposite side. Common associations include left renal colic, left sided pyelonephritis, splenic region referred pain, and left paraspinal musculoskeletal strain. Like R10.A1, R10.A2 should be replaced with the definitive diagnosis code once one has been documented.
R10.A3, Flank pain, bilateral, applies when the patient reports pain on both sides, such as bilateral CVA tenderness on exam during a pyelonephritis workup or bilateral musculoskeletal strain.
R10.A0, Flank pain, unspecified side, is the fallback when laterality is not documented. Query the provider for right or left whenever possible. R10.A1, R10.A2, and R10.A3 carry more clinical specificity and reimbursement value than the unspecified option, and specific codes reduce the risk of medical necessity questions during payer review.
When to Code the Diagnosis Instead of Flank Pain
Per ICD-10-CM Official Guidelines, once a related definitive diagnosis has been established, the symptom code for flank pain is not reported separately; the confirmed diagnosis is coded instead. The most common definitive diagnoses behind flank pain are:
- N20.0: Calculus of kidney
- N20.1: Calculus of ureter
- N39.0: Urinary tract infection, site not specified
- S39.012-: Strain of muscle, fascia and tendon of lower back (7th character required: A for initial encounter, D for subsequent encounter, or S for sequela)
For example, if imaging confirms a right ureteral stone, the claim should report N20.1 rather than R10.A1, even though the patient’s chief complaint was right flank pain.
Documentation Checklist for Accurate Flank Pain Coding
To support clean claims under the new code set, documentation should ideally capture:
- Laterality: right side, left side, or bilateral, since this alone determines whether R10.A0, A1, A2, or A3 applies
- Pain versus tenderness: what the patient reports compared with what is found on physical exam
- Associated symptoms: fever, dysuria, hematuria, nausea, or radiation to the groin
- Definitive diagnosis status: if a cause such as a stone, infection, or strain has been confirmed, that diagnosis should be primary, not the symptom code
Practices that update their EHR templates and coder query workflows to capture these details upfront tend to see fewer back and forth queries between coders and providers, along with higher first-pass claim acceptance rates.
Read more about our blog on clinical documentation improvement for a deeper walkthrough of CDI best practices.
Frequently Asked Questions
What is the ICD-10 code for flank pain?
As of FY2026, effective October 1, 2025, flank pain is coded using R10.A0 (unspecified side), R10.A1 (right side), R10.A2 (left side), or R10.A3 (bilateral), depending on documented laterality.
What is the ICD-10 code for right flank pain?
The ICD-10 code for right flank pain is R10.A1, Flank pain, right side, new for FY2026 and effective October 1, 2025.
Is R10.9 still a valid code for flank pain?
R10.9 (Unspecified abdominal pain) remains billable, but it is no longer the most accurate code for flank pain now that R10.A0 through R10.A3 exist. Use R10.9 only for abdominal pain that is not localized to the flank.
Get Ahead of the FY2026 Coding Changes with ProMantra
ICD-10-CM updates like the new flank pain code family affect more than terminology. They influence medical necessity edits, payer specific coverage policies, and audit risk across an entire claim volume. Practices that continue relying on pre-2025 defaults for flank specific complaints may see increased documentation requests and denials as payers update their edit logic around the new R10.A code set.
Read more about our blog on the consequences of incorrect medical coding to see how coding accuracy affects reimbursement.
ProMantra has supported healthcare providers with accurate, up to date medical coding since 2003, backed by ISO 9001 and ISO 27001 certifications for quality and data security. Our certified coding team monitors every ICD-10-CM, CPT, and HCPCS update so claims consistently reflect the most current and specific codes available, helping reduce denials and protect reimbursement.
Ready to make sure your coding reflects the latest ICD-10-CM updates? Contact ProMantra today to schedule a free coding audit and see how our team can help your practice stay compliant, reduce denials, and get paid faster.
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