What is the best ICD-10 code for idiopathic (ida) malabsorption?

ICD-10 Coding for Idiopathic Malabsorption

For idiopathic malabsorption without a specific underlying cause identified, use ICD-10 code K90.89 (Other intestinal malabsorption) or K90.9 (Intestinal malabsorption, unspecified).

Primary Coding Approach

• K90.89 is the most appropriate code when you have documented malabsorption but cannot identify a specific etiology after appropriate workup, representing "other intestinal malabsorption" not elsewhere classified 1

• K90.9 serves as the fallback code for "intestinal malabsorption, unspecified" when documentation is limited or investigation is incomplete 1

Context-Specific Coding Considerations

If Bile Acid Malabsorption is Suspected or Confirmed

• When idiopathic bile acid malabsorption (IBAM) is the specific diagnosis, K90.89 remains appropriate, as there is no dedicated ICD-10 code for bile acid malabsorption 2, 3

• IBAM affects approximately 10-32% of patients with chronic diarrhea depending on severity thresholds, and SeHCAT retention <15% confirms the diagnosis 4

• Document "idiopathic bile acid malabsorption" or "bile acid diarrhea" in the medical record to justify K90.89 usage 2

If Fat Malabsorption is Documented

• When steatorrhea is present (fecal fat >13 g/day or 47 mmol/day) without identified pancreatic or mucosal disease, use K90.4 (Malabsorption due to intolerance, not elsewhere classified) or K90.89 depending on documentation specificity 5

• Mild steatorrhea (faecal fat 7-14 g/day) commonly occurs with mucosal disease and warrants K90.89 if no specific enteropathy is identified 5

If Small Bowel Bacterial Overgrowth is Present

• SIBO causing malabsorption should be coded as K90.89 when it represents the primary malabsorptive process 5

• SIBO is present in approximately one-third of Crohn's disease patients and increases malabsorption risk 5

Critical Documentation Requirements

• Always document the diagnostic workup performed to justify "idiopathic" designation, including:

  • Negative celiac serology (anti-tissue transglutaminase antibody) 1
  • Normal or non-diagnostic endoscopy with duodenal biopsies 5, 1
  • Exclusion of pancreatic exocrine insufficiency (fecal elastase >100 μg/g) 1
  • Negative inflammatory bowel disease evaluation 5

• Specify the type of malabsorption (fat, carbohydrate, protein, or mixed) to support code selection 5, 1

• Document response to empiric therapy (e.g., cholestyramine for suspected bile acid malabsorption) as this strengthens the diagnostic impression 2, 6

Common Coding Pitfalls to Avoid

• Do not use K59.1 (functional diarrhea) when objective malabsorption is documented, even if the underlying cause is unclear 5

• Avoid K90.0 (celiac disease) unless biopsy-proven villous atrophy and positive serology are present 1

• Do not default to K52.9 (noninfective gastroenteritis and colitis, unspecified) when malabsorption is the primary feature rather than inflammation 5

• Recognize that approximately 50% of patients with idiopathic bile acid malabsorption may spontaneously remit, so reassessment and potential code revision may be needed during follow-up 7

When to Consider Alternative Codes

• If subsequent workup reveals inflammatory bowel disease, recode appropriately (K50.x for Crohn's disease, K51.x for ulcerative colitis), as 13% of initially "idiopathic" cases may eventually be diagnosed with IBD 7

• If short bowel syndrome develops or is identified, use K91.2 (postsurgical malabsorption) instead 1

• For post-cholecystectomy bile acid diarrhea, consider K91.89 (other postprocedural complications) as a secondary code alongside K90.89 2