What are the relevant ICD-10 (International Classification of Diseases, 10th Revision) codes for kidney assessment labs?

ICD-10 Codes for Kidney Assessment Labs

Use ICD-10 code N18.9 (chronic kidney disease, unspecified) as the most practical and widely accepted code for ordering routine kidney assessment labs when the specific stage or etiology is unknown.

Primary ICD-10 Codes for Kidney Function Assessment

For Screening or Initial Assessment

• N18.9 (Chronic kidney disease, unspecified) is the most commonly used code when ordering kidney function labs without a specific diagnosis, as it provides sufficient justification for renal panel testing while maintaining high specificity (>99%) in administrative databases 1
• Z13.89 (Encounter for screening for other disorder) can be used for true screening in asymptomatic patients without known kidney disease 1

For Known CKD Stages

When kidney function is already established, use stage-specific codes based on eGFR categories 2:

• N18.1 - CKD Stage 1 (GFR ≥90 mL/min/1.73 m²)
• N18.2 - CKD Stage 2 (GFR 60-89 mL/min/1.73 m²)
• N18.3 - CKD Stage 3 (GFR 30-59 mL/min/1.73 m²)
  • N18.30 - CKD Stage 3, unspecified
  • N18.31 - CKD Stage 3a (GFR 45-59 mL/min/1.73 m²)
  • N18.32 - CKD Stage 3b (GFR 30-44 mL/min/1.73 m²)
• N18.4 - CKD Stage 4 (GFR 15-29 mL/min/1.73 m²)
• N18.5 - CKD Stage 5 (GFR <15 mL/min/1.73 m²)
• N18.6 - End-stage renal disease (ESRD) - though KDIGO guidelines recommend avoiding this terminology in favor of "CKD G5D" for dialysis patients 2, 3

For Acute Kidney Conditions

• N17.9 (Acute kidney failure, unspecified) for suspected or confirmed acute kidney injury (AKI), though ICD-10 coding has poor sensitivity (25.7-35.8%) for identifying biochemically-defined AKI 4
• N17.0-N17.2 for specific AKI etiologies when known (prerenal, intrinsic, postrenal) 4

Laboratory Components Justified by These Codes

Basic Metabolic Panel (BMP)

• The BMP includes serum creatinine, which is automatically used by laboratories to calculate and report eGFR according to KDIGO standards 5
• Clinical laboratories must automatically report eGFR alongside serum creatinine using validated equations (CKD-EPI or MDRD), rounded to the nearest whole number in units of mL/min per 1.73 m² 5
• Values below 60 mL/min per 1.73 m² should be flagged as low by the laboratory 5

Comprehensive Metabolic Panel (CMP)

• Includes all BMP components plus liver function tests and albumin 5
• Justified by the same ICD-10 codes as BMP when comprehensive assessment is needed 1

Urinalysis with Microscopy

• R80.9 (Proteinuria, unspecified) or R82.9 (Other abnormal findings in urine) can be added when assessing for albuminuria or proteinuria 2
• KDIGO guidelines emphasize that CKD assessment requires both GFR and albuminuria categories (A1-A3) for complete classification 2

Urine Albumin-to-Creatinine Ratio (ACR)

• Use R80.9 or specific CKD codes (N18.x) to justify ACR testing 2
• Albuminuria categories: A1 (ACR <30 mg/g), A2 (ACR 30-300 mg/g), A3 (ACR >300 mg/g) 2

Critical Documentation Considerations

Common Pitfalls to Avoid

• Do not rely solely on ICD-10 codes for research or quality monitoring - ICD-10 coding has very poor sensitivity (25.7-43.8%) for identifying true kidney disease compared to biochemical definitions 4, 6
• Avoid outdated terminology - Never use codes or documentation referring to "renal failure," "ESRD," "renal insufficiency," or "renal impairment" as these terms are discouraged by KDIGO 2
• ICD-10 codes underestimate the true prevalence of kidney disease by approximately 40-45% compared to KDIGO biochemical criteria 6

Accuracy of ICD-10 Coding

• Positive predictive value (PPV) for CKD Stages 3-5 ranges from 80-86% when using two ICD-10 codes within 90 days of laboratory confirmation 1
• Specificity is consistently high (>86-99%) but sensitivity remains poor, meaning many patients with kidney disease will not be captured by ICD-10 codes alone 1, 4, 6
• The algorithm of two CKD codes compared with a lab value ±90 days achieves the highest PPV (86.07% for ICD-10) 1

Enhanced Documentation Strategy

• When documenting CKD, use the complete CGA classification: Cause + GFR category (G1-G5) + Albuminuria category (A1-A3) 2, 3
• For dialysis patients, document as "CKD G5D" followed by modality (hemodialysis, peritoneal dialysis) and frequency 3
• Include the underlying cause (diabetic kidney disease, hypertensive nephrosclerosis, etc.) whenever possible 3

Real-World Implementation

• Under-perception of CKD among non-nephrologist physicians is the primary cause of under-diagnosis, not lack of laboratory testing 7
• The majority of CKD patients (51.6-91.1%) receive serum creatinine tests from non-nephrologists, but CKD-staging diagnoses are mainly made by nephrologists (52.3-64.8%) 7
• In one large study, 61.4% of patients with confirmed CKD by laboratory criteria had no CKD-related ICD codes in their medical records 7