What is the workup for suspected lactose intolerance?

Diagnostic Workup for Lactose Intolerance

The recommended diagnostic approach for suspected lactose intolerance should begin with a 2-week dietary elimination trial followed by reintroduction, as this is the simplest and most economically sound initial diagnostic method. 1

Initial Assessment

• Document relationship between dairy consumption and symptoms:

  • Record all food intake with specific attention to dairy products
  • Track timing of symptoms after dairy intake
  • Evaluate symptom patterns (bloating, abdominal pain, flatulence, diarrhea)
  • Use tools like Bristol stool chart to assess stool consistency and frequency 1

• Basic laboratory testing:

  • Complete blood count (CBC)
  • Inflammatory markers (CRP, ESR)
  • Albumin, electrolytes, liver function
  • Nutritional parameters (vitamin B12, folate, ferritin, calcium) 1
  • Consider serological testing for celiac disease (TTG antibodies)
  • Stool tests for inflammation (fecal calprotectin) and infection 1

Diagnostic Algorithm

1. Elimination Trial (First-Line):

   • Remove all milk/dairy products for 2 weeks
   • Observe for symptom improvement
   • Reintroduce dairy and monitor for symptom recurrence 1

2. Hydrogen Breath Test (If elimination trial is inconclusive):

   • Most widely used diagnostic test for lactose malabsorption
   • Protocol: Overnight fast → Ingestion of 25-50g lactose → End-expiratory breath samples at 15-30 minute intervals for 3 hours
   • Positive result: Rise in hydrogen >20 parts per million
   • Note: Has a 25% false negative rate 1, 2

3. Genetic Testing (Alternative):

   • Testing for lactase-persistent alleles (LCT-13,910 C/T)
   • High sensitivity (89%) and specificity (94%) in populations with high prevalence of lactase-persistent alleles
   • May be more reliable than hydrogen breath testing in certain populations 1

Important Considerations

• Prevalence varies by ethnicity:

  • 10% in Northern Europeans
  • 60% in Asians
  • Up to 90% in Chinese populations 1
  • Up to 80% in Blacks and Latinos 3

• Secondary causes of lactose intolerance:

  • Intestinal damage from acute infections
  • Celiac disease
  • Small intestinal bacterial overgrowth (SIBO)
  • Medication-induced intestinal damage 1

• Distinguish from milk protein allergy:

  • Lactose intolerance is a physiological condition due to lactase deficiency
  • Milk protein allergy is an immune-mediated reaction
  • Different diagnostic approaches are required for each 1

Common Pitfalls to Avoid

• Skipping the elimination trial and proceeding directly to more expensive testing 1

• Failing to consider secondary causes of lactose intolerance that require specific treatment 1

• Relying solely on blood tests without clinical correlation, which can lead to unnecessary dietary restrictions 1

• Confusing intolerance with allergy, which are distinct conditions requiring different diagnostic methods 1

• Using IgG antibody testing for food elimination diets, which is not recommended for gastrointestinal disorders including lactose intolerance 1

• Overlooking that many patients who believe they are lactose intolerant may not actually have impaired lactose digestion 3

• Assuming complete avoidance is necessary when most lactose-intolerant individuals can tolerate up to 12 oz of milk daily without symptoms 3, 4

The diagnostic approach should be systematic, starting with the least invasive and most cost-effective method (elimination trial), and progressing to more specific tests only when necessary. This approach ensures accurate diagnosis while minimizing unnecessary testing and dietary restrictions.