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ICD-10 Coding for Elevated BUN(R79.9, N18.3, E86.0)

Complete ICD-10-CM coding and documentation guide for Elevated BUN. Includes clinical validation requirements, documentation requirements, and coding pitfalls.

Also known as:

High Blood Urea NitrogenIncreased BUN

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Related ICD-10 Code Ranges

Complete code families applicable to Elevated BUN

R79.9Primary Range

Abnormal findings of blood chemistry

Used for elevated BUN without a specific diagnosis.

N18.3-N18.9

Chronic kidney disease (CKD) stages 3-5

Used when elevated BUN is due to CKD.

E86.0

Dehydration

Used when elevated BUN is due to dehydration.

Code Comparison: When to Use Each Code

Compare key differences between these codes to ensure accurate selection

CodeDescriptionWhen to UseKey Documentation
R79.9Abnormal findings of blood chemistry, unspecifiedUse when elevated BUN is noted without a specific underlying diagnosis.
  • BUN >20 mg/dL on ≥2 tests
  • No documented CKD, AKI, or dehydration
N18.3Chronic kidney disease, stage 3Use when CKD stage 3 is documented with elevated BUN.
  • eGFR 30-59 for ≥3 months
  • Documented CKD stage
E86.0DehydrationUse when dehydration is the cause of elevated BUN.
  • BUN:Cr ratio >20:1
  • Clinical signs of dehydration

Clinical Decision Support

Always review the patient's clinical documentation thoroughly. When in doubt, choose the more specific code and ensure documentation supports it.

Key Information: ICD-10 code for elevated BUN

Essential facts and insights about Elevated BUN

The ICD-10 code for elevated BUN without a specific diagnosis is R79.9. Use this code when elevated BUN is noted without an underlying condition like CKD or dehydration.

Primary ICD-10-CM Codes for elevated bun

R79.9
Abnormal findings of blood chemistry, unspecified
Billable Code

Decision Criteria

clinical Criteria

  • BUN >20 mg/dL without specific diagnosis

coding Criteria

  • No CKD or AKI documented

Applicable To

  • Elevated BUN without a specific diagnosis

Excludes

  • Chronic kidney disease (N18.-)
  • Acute kidney failure (N17.-)

Clinical Validation Requirements

  • BUN >20 mg/dL on ≥2 tests
  • No documented CKD, AKI, or dehydration

Code-Specific Risks

  • Incorrect use when a specific diagnosis is present

Coding Notes

  • Ensure no specific diagnosis is documented before using R79.9.
View Full Code Details

Ancillary Codes

Additional codes that should be used in conjunction with the main diagnosis codes when applicable.

Dehydration

E86.0
Use alongside R79.9 when dehydration is confirmed.

Differential Codes

Alternative codes to consider when ruling out similar conditions to the primary diagnosis.

Chronic kidney disease, stage 3

N18.3
Use when BUN >30 mg/dL with eGFR 30-59 for ≥3 months.

Dehydration

E86.0
Use when BUN:Cr ratio >20:1 with clinical signs of dehydration.

Abnormal findings of blood chemistry, unspecified

R79.9
Use R79.9 if no CKD is documented.

Documentation & Coding Risks

Avoid these common documentation and coding issues when documenting Elevated BUN to ensure proper reimbursement, maintain compliance, and reduce audit risk. These guidelines are particularly important when using ICD-10 code R79.9.

Impact

Clinical: May lead to misdiagnosis or inappropriate treatment., Regulatory: Non-compliance with coding standards., Financial: Potential claim denials due to insufficient documentation.

Mitigation Strategy

Ensure repeat tests are documented., Include clinical context for elevated levels.

Impact

Reimbursement: May lead to claim denials if incorrect code is used., Compliance: Non-compliance with coding guidelines., Data Quality: Inaccurate data representation in patient records.

Mitigation Strategy

Use the specific diagnosis code instead of R79.9.

Impact

Using R79.9 when a specific diagnosis is documented.

Mitigation Strategy

Ensure thorough review of patient records for specific diagnoses.

Documentation errors, coding pitfalls, and audit risks are interconnected aspects of medical coding and billing. Addressing all three areas helps ensure accurate coding, optimal reimbursement, and regulatory compliance.

Frequently Asked Questions

Common questions about ICD-10 coding for Elevated BUN, with expert answers to help guide accurate code selection and documentation.

Documentation Templates for Elevated BUN

Use these documentation templates to ensure complete and accurate documentation for Elevated BUN. These templates include all required elements for proper coding and billing.

Nephrology Progress Note

Specialty: Nephrology

Required Elements

  • Current BUN level
  • Associated clinical findings
  • Clinical attribution
  • Management plan

Example Documentation

**BUN Documentation Module** - Current BUN: __ mg/dL (Trend: ___ → ___ → ___ over ___ days) - Associated Findings: ☐ Oliguria (<500 mL/24h) ☐ Elevated Cr (__ mg/dL) ☐ BUN:Cr ratio __:1 - Clinical Attribution: ☐ Dehydration (E86.0) - Signs: _______ ☐ CKD Stage __ (N18.__) - eGFR __, stable/declining ☐ Medication effect (T45.1X5A if antibiotic-induced) ☐ Other: _______ - Management Plan: _______

Examples: Poor vs. Good Documentation

Poor Documentation Example
BUN elevated.
Good Documentation Example
BUN 55 mg/dL (7/12/25 AM) and 58 mg/dL (7/13/25 AM) in setting of oliguria (<400 mL/24h) and +2 pedal edema; attributed to acute-on-chronic CKD (baseline eGFR 35, current eGFR 22).
Explanation
The good example provides specific lab values, clinical context, and a clear attribution to CKD.

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