What ICD-10 codes are used for elevated Rheumatoid Arthritis (RA) and Cancer Antigen 125 (CA125)?

ICD-10 Coding for Elevated Rheumatoid Factor and CA125

For elevated rheumatoid factor (RF) in the context of rheumatoid arthritis, use M05 codes for seropositive RA; for elevated CA125, use R97.8 (other abnormal tumor markers) or the specific code for the underlying condition causing the elevation.

Coding for Elevated Rheumatoid Factor

Seropositive Rheumatoid Arthritis (M05 Series)

• M05 diagnosis codes identify rheumatoid factor positive ("seropositive") RA with high accuracy - sensitivity of 76% and positive predictive value of 82% when RF or anti-CCP lab results serve as the gold standard 1
• The M05 code series remains consistent across approximately 90% of consecutive visits, demonstrating reliable coding stability 1
• Specific M05 subcodes should be selected based on organ involvement and disease manifestations 1

Seronegative Rheumatoid Arthritis (M06 Series)

• M06 codes identify seronegative RA with comparable sensitivity and positive predictive values to M05 codes 1
• Use M06 series when RF and anti-CCP are negative but clinical diagnosis of RA is established 1

Coding for Elevated CA125

Primary Code Selection

• R97.8 (Other abnormal tumor markers) is the appropriate code for isolated CA125 elevation without identified malignancy 2
• This code captures the laboratory abnormality when the clinical significance remains under investigation

Important Clinical Context Affecting Code Selection

CA125 elevation occurs in multiple benign conditions and should not automatically suggest malignancy:

• Endometriosis and gynecologic conditions: CA125 elevation in premenopausal patients with endometriosis should not elevate concern for malignancy 3
• Rheumatoid arthritis: CA125 is frequently elevated in RA patients (10.8% show abnormally high levels) and does not indicate cancer presence 4, 5
• RA-associated interstitial lung disease: CA125 levels are significantly elevated in RA-ILD patients, with levels above 35 U/mL increasing RA-ILD risk 6-fold 6
• Ascites of any cause: Essentially all patients with ascites or pleural fluid of any cause have elevated serum CA125, including men 2
• Other benign conditions: Pelvic inflammatory disease, menstruation, adenomyosis, and benign cysts all elevate CA125 2, 3

When to Code the Underlying Condition Instead

• If endometriosis is diagnosed: Use N80.x codes (endometriosis by location) as the primary diagnosis 3
• If RA-ILD is present: Use M05.1x (rheumatoid lung disease) as this captures both the RA and pulmonary involvement 6
• If ascites is present: Code the underlying cause of ascites (cirrhosis, heart failure, etc.) rather than focusing on CA125 elevation 2
• If ovarian cancer is confirmed: Use appropriate C56.x or C57.x codes based on pathology 2

Critical Coding Pitfalls to Avoid

Do Not Automatically Code for Malignancy

• Small increases in tumor markers in RA patients do not warrant coding for occult neoplasm - these elevations are common even with controlled disease and are not related to actual cancer 4
• In one study of 100 RA patients with elevated tumor markers, only 1 of 2 neoplasms found was related to the elevated marker 4

CA125 Testing Should Be Avoided in Certain Contexts

• Testing serum for CA125 is not helpful in the differential diagnosis of ascites and should not be performed in patients with ascites of any type 2
• Patients with ascites may be unnecessarily referred for gynecologic surgery based on elevated CA125, even if ovaries were previously removed 2

Correlation with Disease Activity

• No correlation exists between tumor markers (including CA125) and RA disease activity as measured by DAS28 4, 5
• CA125 elevation in RA correlates with specific complications (like ILD) rather than general disease severity 6

Practical Coding Algorithm

Step 1: Determine if RF elevation is associated with clinical RA diagnosis

• Yes → Use M05.x (seropositive) or M06.x (seronegative) based on serology 1
• No → Use M79.0 (rheumatism, unspecified) or R76.0 (raised antibody titer) for isolated RF elevation

Step 2: Determine the clinical context of CA125 elevation

• Known endometriosis → Code N80.x 3
• Known RA with ILD → Code M05.1x 6
• Ascites present → Code underlying cause, not CA125 2
• Isolated elevation under investigation → Code R97.8

Step 3: Add secondary codes for any complications or associated conditions

• RA-ILD: Add J84.x for interstitial lung disease if using M05.1x 6
• Multiple elevated tumor markers: Consider coding each separately if clinically relevant 4, 5