How lactose intolerance is tested

If you suspect lactose is your problem, it's worth finding out properly rather than cutting out dairy on a hunch. Here's how lactose intolerance is actually diagnosed in Australia — and which methods are worth your time.

The main testing options

1. Hydrogen breath test — the common clinical test

You drink a measured lactose solution (typically 25–50 g of lactose), then breathe into a device at intervals over the next 2–3 hours. If lactose isn't being digested, gut bacteria ferment it and produce hydrogen, which shows up in your breath; a rise of 20 ppm or more above your baseline is counted as a positive result. It's a direct, widely used test — pooled studies put its accuracy at roughly 88% sensitivity and 85% specificity — usually arranged through your GP or a pathology clinic.

One honest caveat: an estimated 2.5–15% of results come back falsely negative, often because some people don't produce much hydrogen even when they aren't digesting the lactose. That's why your clinician reads the result alongside your symptoms rather than in isolation.

2. Elimination and reintroduction

Under guidance — ideally a dietitian's — you remove lactose for a period, then reintroduce it, watching how symptoms respond. Done properly, it's a reliable, practical way to confirm the link.

3. Other tests

Some clinics offer lactose tolerance blood tests or genetic tests for the lactase gene variant. These have their place but each has limitations worth discussing with a professional.

Why proper testing is worth it

Because lactose intolerance shares symptoms with IBS, coeliac disease and other conditions, confirming it means you're not needlessly cutting out dairy — or missing something else that needs treating.

What happens after diagnosis

If it's confirmed, the plan is reassuring: work out your threshold, lean on lower-lactose foods and lactose-free products, and use a lactase supplement when you want regular dairy. See what helps for the supplements we tested.

More on getting tested

• What does a lactose intolerance test cost in Australia?
• Can my GP test me for lactose intolerance?
• At-home tests — what's legit, and what to avoid

When to see a doctor

Start with your GP — they can arrange the appropriate test and rule out other causes. Definitely see a doctor first if symptoms are severe, sudden, or come with weight loss or blood in the stool.