Lactose Intolerance: Symptoms, Causes, Diagnosis & Management Overview

Lactose intolerance = inability to digest lactose due to lactase deficiency.

Symptoms (30 min–2 hr post-dairy)

• Bloating, flatulence, abdominal cramps, diarrhea (osmotic).
• Nausea, borborygmi, urgency.
• Severity dose-dependent; varies by residual lactase.

Causes

• Primary (genetic downregulation) — most common.
• Secondary (mucosal injury: celiac, infection, IBD).
• Congenital (rare).

Diagnosis

• H₂ breath test (rise >20 ppm above baseline).
• Lactose tolerance test (Δ glucose <20 mg/dL).
• Genetic test (C/T-13910) for primary.
• Therapeutic trial: 2-wk strict lactose-free → symptom resolution → challenge.

Management

• Dietary modification (reduce/avoid lactose).
• Lactase supplements.
• Lactose-free dairy products.
• Treat underlying cause if secondary.

Not an allergy; no anaphylaxis risk. Distinguish from cow milk protein allergy (immune-mediated).