How do you diagnose normal?

Dr Kathryn Fox is an Australian medical doctor and bestselling crime writer, best known for her forensic thrillers featuring pathologist Dr Anya Crichton. Drawing on her medical expertise, she crafts gripping, authentic crime fiction and is also a passionate advocate for forensic medicine education and public engagement. Her columns appear every Monday and Thursday.

One of the hardest things to recognise in medicine isn’t disease.

It’s normal.

A usually pale patient arrives deeply tanned for a routine blood pressure check. In summer, that’s unremarkable. In winter, the brain quietly runs through possibilities. Fake tan? Recent travel? Internet obtained supplements? A hormonal issue? Something more concerning?

One appearance, multiple explanations, some entirely harmless, others not. In this patient, it seemed a variety of symptoms had been treated independently by a series of different doctors. No one had looked at her as a whole person.

Blood tests showed an underactive thyroid gland but a rapid pulse rate, diarrhoea and weight loss, which didn’t fit with that. This tan had only recently developed, oddly including dark lines on the creases of her palms. All she wanted from me was to ask if she should be taking thyroid replacement medication.

Alarm bells rang.

I suspected a rare endocrine condition called Addison’s disease. There’s an old medical saying: when you hear hoofbeats, think horses, not zebras – meaning common conditions occur commonly. For a moment, colleagues assumed I’d gone straight to the zebra. I’d seen a case of Addison’s once before, and tests confirmed that’s what my patient had. She dramatically improved with immediate treatment.

Doctors are trained to look for patterns. When we detect a pattern or recognise one we’ve seen before, we investigate.

Buoyed by my diagnostic skills, I was ready for the next challenge. When a middle-aged woman came in with enlarged hands, coarse facial features, shoes that no longer fit and a head too large for standard hats, my internal checklist lit up almost instantly. Friends had told her she looked like a female version of Andre the Giant, the famous wrestler/actor who was diagnosed with acromegaly caused by a tumour that produced excess growth hormone. It’s rare, but it’s the kind of diagnosis you don’t want to miss.

My patient’s hands, feet and facial features did seem to align perfectly with the textbook description.

And then I asked a different question.

“Do you have any photos of your family?”

She scrolled through her phone and turned it toward me. Row after row of familiar bone structure. Strong features. Broad noses. Heavy brows. Large hands. The same look repeated across generations.

Acromegaly doesn’t run through entire extended families.

What I had been preparing to diagnose wasn’t pathology, it was inheritance.

In that moment, the concern I’d been carrying quietly dissolved – replaced with humility.

Medicine is very good at spotting abnormality. Sometimes it can be a little too good.

“Normal” is one of the most complicated concepts in healthcare. Data gives us averages, ‘within normal range’, standard deviations and red flags. But humans aren’t born to fit neatly into statistical boxes. They’re shaped by genetics, ancestry, culture and variation.

Big hands on one person raise questions.

Big hands across a family answers them.

This is where general practice quietly excels. Seeing people over time, seeing siblings, parents, children. Hearing stories. Recognising what has changed – and what has always been there.

Patients frequently ask, “Is this normal?”

Normal is often revealed by context, not by tests. Sometimes the most reassuring answer isn’t a scan or a blood test, but perspective: “This is how your family is built.” “This hasn’t changed – we’ve just noticed it.” In other words, “This is normal for you.”

That doesn’t mean dismissing concern. It means grounding medicine in reality instead of automatically assuming something is wrong.

Medicine rightly trains doctors to fear what they might miss. Missing serious illness can be catastrophic. But the flip side of vigilance is remembering that not every deviation from the average is dangerous.

Normal isn’t a number. It isn’t a checklist. And it certainly isn’t a single body shape, facial structure or measurement. The trick is to zoom out far enough to see the whole picture.

Sometimes the most important diagnosis we make isn’t a disease at all. It’s recognising normal – and appreciating it.