Lactase deficiency is a common and normal digestive condition, but it often goes undiagnosed or misunderstood. Many people live with symptoms for years without realizing there is a specific reason dairy causes discomfort.
Understanding what lactase deficiency is and how it is evaluated can help patients and parents know when testing is helpful and when it may not be necessary.
What Is Lactase Deficiency?
Lactase is an enzyme produced in the small intestine. Its job is to break down lactose, the natural sugar found in dairy products.
Lactase deficiency occurs when the body does not produce enough of this enzyme. When lactose is not properly broken down, it passes into the colon where bacteria ferment it. This process leads to gas, bloating, abdominal pain, and diarrhea.
Lactase deficiency is the underlying cause of lactose intolerance symptoms.
Why Lactase Levels Can Be Low
There are several reasons lactase production may be reduced.
Primary lactase deficiency
This is the most common type. Lactase production naturally decreases with age, often beginning in late childhood or adolescence. This is genetically programmed and very normal.
Secondary lactase deficiency
This occurs when the lining of the small intestine is temporarily damaged. Common causes include viral stomach infections, celiac disease, inflammatory bowel disease, or prolonged diarrhea. Lactase levels may improve once the gut heals.
Congenital lactase deficiency
This is extremely rare and present from birth. Infants with this condition cannot tolerate breast milk or standard formula.
Do Doctors Always Test for Lactase Deficiency?
Not always. In many cases, lactase deficiency can be identified based on symptoms and response to dietary changes.
If symptoms improve with lactose reduction or lactose free products, formal testing may not be necessary. However, testing can be helpful when the diagnosis is unclear or when symptoms are severe, persistent, or atypical.
Common Tests for Lactase Deficiency
Hydrogen breath test
This is the most commonly used test. After drinking a lactose containing solution, breath samples are collected over several hours. Elevated hydrogen levels suggest lactose is not being properly digested.
This test is noninvasive but requires preparation and time.
Lactose tolerance test
Blood glucose levels are measured after consuming lactose. If glucose levels do not rise, it suggests lactose is not being broken down and absorbed.
This test is used less often today.
Stool acidity test
This test is sometimes used in infants and young children. Undigested lactose produces acidic stool, which can be measured.
Small intestine biopsy
This is rarely done solely to diagnose lactase deficiency. It may be considered if a child is undergoing endoscopy for another reason and secondary causes are being evaluated.
When Testing Is Most Helpful
Testing may be useful when:
• Symptoms do not clearly correlate with dairy intake
• Symptoms persist despite lactose restriction
• Weight loss or growth concerns are present
• There is concern for another underlying intestinal condition
In these cases, testing helps guide next steps rather than guessing.
What Happens After a Diagnosis?
A diagnosis of lactase deficiency does not mean dairy must be completely avoided.
Most people tolerate:
• Lactose free milk and dairy products
• Small portions of dairy with meals
• Hard cheeses and yogurt
• Lactase enzyme supplements
Management focuses on symptom control and maintaining adequate calcium and vitamin D intake.
The Bottom Line
Lactase deficiency is common, normal, and manageable. Doctors do not always need formal testing to diagnose it, but testing can be helpful in certain situations. Understanding the cause of symptoms allows for informed choices rather than unnecessary restriction.
If digestive symptoms continue despite dietary changes, further evaluation may be needed to rule out other conditions.
Kindly,
Renee
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