Hemochromatosis and your 23andMe raw data: checking HFE variants

A genetics explainer · Updated June 2026

23andMe & raw DNA

How your body handles iron

Iron is essential — it carries oxygen in your red blood cells and powers dozens of enzymes — but the body has no active way to get rid of a surplus. There is a route in (absorption through the gut) and only passive routes out (shed cells, blood loss). With no "off switch" for excretion, the body's only real lever is how much iron it lets in from food, so regulation happens almost entirely at the point of absorption.

The master regulator of that process is hepcidin, a hormone made by the liver. When iron stores are high, hepcidin rises and tells the gut to stop releasing iron into the bloodstream; when stores are low, hepcidin falls and absorption increases. In a healthy system this feedback loop keeps total body iron in a fairly narrow band for a lifetime.

Hereditary hemochromatosis is what can happen when that loop is set too loose. The HFE gene helps the liver sense how much iron is around and produce the right amount of hepcidin. Certain HFE variants blunt that signal, so hepcidin stays lower than it should and the gut keeps absorbing iron as if stores were empty even when they are already full. Over many years — usually decades — the surplus can accumulate in the liver, heart, pancreas, and joints. That slow, silent build-up is why the condition often goes unnoticed until midlife, and why it is worth understanding rather than fearing.

What hereditary hemochromatosis is

Hereditary hemochromatosis is a condition in which the body absorbs and stores too much iron from food. It is one of the most common inherited conditions in people of Northern European ancestry, which is part of why the variants behind it are so well studied. When excess iron does cause problems, symptoms can include fatigue, joint pain, and abnormal liver tests — but, crucially, many people with the underlying genetics never develop iron overload at all.

The most common form is linked to the HFE gene. Two variants in this gene are the ones people typically check, and both are reported in standard 23andMe-style raw data files.

The HFE variants in your hemochromatosis 23andMe raw data

There are two HFE markers worth knowing:

• C282Y — reference ID rs1800562. This is the variant most strongly associated with iron overload.
• H63D — reference ID rs1799945. This variant carries a weaker association on its own.

To find them, open your raw data .txt file in any text editor and search (Ctrl+F or Cmd+F) for the rsid — for example rs1800562. The matching row shows the marker's chromosome, position, and your genotype: the two letters you inherited at that spot. If you'd rather not scroll through a text file, our free DNA explorer lets you search these markers in your own file right in the browser, with nothing uploaded.

What the genotypes mean

Each marker reports two letters, one from each parent. Broadly:

• C282Y homozygous (two copies of the C282Y variant) carries the highest genetic risk of iron overload, and is the genotype most often linked to clinical hemochromatosis.
• Compound heterozygous (one copy of C282Y and one of H63D) carries a lower risk than C282Y homozygous.
• A single copy of either variant makes you a carrier. Most carriers never develop iron overload.
• No variant at either marker means the common HFE-related risk is not present.

The exact letters that represent each variant depend on how the file reports the strand, which is one more reason to use a tool rather than eyeball the raw letters. See our guide to the best tools to interpret 23andMe raw data for safe ways to translate genotypes into plain language.

A useful way to think about it: C282Y homozygous is the genotype that iron studies pay closest attention to, because among people who do go on to develop clinical iron overload, it is by far the most common underlying combination. Compound heterozygous (one C282Y, one H63D) sits in a lower-risk middle ground — most such people never accumulate meaningful iron, though a minority, particularly if they have another risk factor, might. A single copy of either variant makes you a carrier: relevant to family and to your children's genetics, but rarely a source of iron overload by itself. And two copies of H63D, without any C282Y, is generally considered a low-risk combination on its own. None of these categories is a verdict — they simply sort your result into "worth checking iron studies" versus "reassuring," and only a doctor working from blood tests can turn that into anything more definite.

Why penetrance is low and variable

This is the part that matters most. Carrying an HFE variant — even the higher-risk C282Y homozygous genotype — does not mean you have hemochromatosis or that you will develop it. The genetics describe a predisposition, not a diagnosis. Penetrance, meaning the share of people with the genotype who actually develop iron overload, is low and highly variable, especially in women. Many people with these variants live their whole lives with normal iron levels.

Other factors — sex, age, blood loss, diet, alcohol, and other genes — all influence whether iron actually accumulates. Menstruation and pregnancy, for example, both remove iron from the body, which is one reason iron overload tends to appear later and less often in women than in men. Someone can carry the highest-risk genotype and, thanks to a lifetime of regular blood loss or simply favourable modifier genes, keep entirely normal iron levels. So a raw-data result is a reason to ask a question, not an answer in itself. This is a recurring theme with health-risk variants: with BRCA and breast and ovarian cancer risk, for instance, the catch is the opposite but just as important — the chip checks only a few variants, so an absent result is not an all-clear.

What iron overload can feel like — and why it hides

If iron does slowly accumulate, the early signs are famously vague and easy to attribute to ordinary life. Fatigue, joint aches (classically in the knuckles), reduced libido, and a general "off" feeling are common early complaints, and none of them points obviously at iron. Because the build-up takes years, many people feel nothing at all until midlife. When it does progress, the organs that store the most iron are the ones that show it: the liver (abnormal liver enzymes, and over time scarring), the pancreas (which can contribute to diabetes), the heart (rhythm problems or weakened pumping), and the joints. Some people notice a bronze or grey tint to the skin.

The important message is not that these things will happen — for most people with HFE variants they never do — but that when iron overload is real, its symptoms are unremarkable enough to be missed for a long time. That is exactly why a genetic heads-up has value: it can prompt the simple blood tests that catch a problem while it is still fully reversible, long before any of these symptoms would appear.

How a diagnosis is actually confirmed

Hemochromatosis is confirmed by measuring iron in your blood, not by reading DNA. The standard first tests are serum ferritin and transferrin saturation. Ferritin reflects how much iron your body has stored, while transferrin saturation reflects how much iron is being carried in the blood right now; in iron overload, both tend to run high, and transferrin saturation in particular often rises first. If you want to understand these numbers, our explainers on what your ferritin level means and what causes high ferritin walk through how they are read and the many things besides hemochromatosis that can move them.

If those tests are elevated, a doctor decides on any further evaluation — which might include repeat testing, imaging to estimate liver iron, or genetic confirmation. Genetic results can support the picture, but iron studies ordered and interpreted by a clinician are what establish whether there is real iron overload to act on. It is worth stressing the direction of that logic: the blood tests confirm the condition, and the genetics only help explain it. A raw-data variant never skips that step.

The good news: it is very treatable when caught

One reason awareness of hemochromatosis is worthwhile is that, when it is caught, the treatment is strikingly simple and effective. The mainstay is therapeutic phlebotomy — removing blood on a schedule set by a doctor, much like donating. Because so much of the body's iron lives in red blood cells, drawing off blood pulls iron out of circulation and forces the body to draw down its stored surplus. Ferritin is tracked over time until it returns to a healthy range, after which many people need only occasional maintenance sessions. It is a well-established, low-tech treatment.

Caught early — before organ damage — people managed this way generally have a normal life expectancy. That is the whole argument for paying attention to an HFE result: not alarm, but the chance to check a couple of inexpensive blood tests and, if needed, act early on something that is very manageable. Treatment decisions, schedules, and monitoring belong entirely with your doctor; this is not something to attempt to manage on your own.

Why raw data is not a diagnosis

It is worth being explicit about why your 23andMe file, on its own, cannot tell you whether you have hemochromatosis. Genotype describes predisposition, not present-tense reality; penetrance is low and shaped by sex, age, and lifestyle; and consumer raw data can contain occasional genotyping errors at any single marker. For all three reasons, a clinically important call is never made from an unconfirmed raw-data letter. The file is a good prompt for a conversation with a doctor — not, and never, the answer itself.

Looking it up safely

If you don't have your file yet, start with our step-by-step guide to downloading your 23andMe raw data. Once you have it, the safest way to read any health marker is on your own device — your genome is the one piece of data you can never change, and most interpretation sites ask you to upload it to their servers first. For the bigger picture of what your file can and can't tell you, see our complete guide to 23andMe raw data.

The takeaway

Checking your HFE variants in your raw data is a reasonable, useful thing to do — hemochromatosis is common, the markers are well studied, and the condition is very treatable when caught early. But hold the result lightly. Even the highest-risk C282Y homozygous genotype is a predisposition, not a diagnosis, and most people who carry HFE variants never develop iron overload. If your result falls in a higher-risk category, the sensible next move is not to change your diet or start donating blood on your own — it is to mention it to your doctor and ask about a simple pair of blood tests, ferritin and transferrin saturation. Those tests, not your DNA file, are what actually confirm whether there is iron to manage. Genetics can open the conversation; clinical iron studies and your doctor finish it.

Frequently asked questions

Which rsids show hemochromatosis in 23andMe raw data?

The two HFE markers most people check are C282Y (rs1800562) and H63D (rs1799945). Search your raw .txt file for those reference IDs to find your genotype at each.

Does a C282Y variant mean I have hemochromatosis?

No. A variant indicates a genetic predisposition, not a diagnosis. Penetrance is low and variable, and many people with HFE variants never develop iron overload. Confirmation requires blood iron tests ordered by a doctor.

How is hemochromatosis confirmed if not by DNA?

It is confirmed with iron studies — serum ferritin and transferrin saturation — and a doctor's evaluation. Genetic results can support the picture, but the blood tests determine whether real iron overload is present.

What does HFE actually do?

The HFE gene helps the liver sense how much iron the body has and produce the right amount of hepcidin, the hormone that controls iron absorption. Common HFE variants blunt that signal, so the gut keeps absorbing iron even when stores are already full. Over years, that surplus can build up in organs.

What's the difference between C282Y homozygous and compound heterozygous?

C282Y homozygous means two copies of the C282Y variant and carries the highest genetic risk of iron overload. Compound heterozygous means one C282Y and one H63D, which carries a lower risk. Neither is a diagnosis — both only indicate predisposition, confirmed or ruled out by iron studies.

Why do many people with HFE variants never get iron overload?

Penetrance is low and variable. Whether iron actually accumulates depends on sex, age, blood loss, diet, alcohol, and other genes. Menstruation and pregnancy remove iron, so overload appears less often in women. Many people with even the higher-risk genotype keep normal iron levels for life.

How is iron overload treated if it's found?

The standard treatment is therapeutic phlebotomy — removing blood on a schedule set by a doctor, similar to donating. It draws iron out of the body and is simple and effective, especially when started early. Treatment and monitoring belong entirely with a doctor.

Can raw DNA data be wrong about an HFE variant?

Yes. Consumer raw data is generated at scale and can contain occasional errors at any single marker. That is one more reason a clinically important result is never based on an unconfirmed raw-data letter, and why iron studies and a doctor confirm the picture.