Two men can walk out of the same collection centre with the same testosterone result. One feels steady. The other is losing hair, carrying weight around the middle, and flat by three in the afternoon. Two women can share an estrogen result and have entirely different cycles, moods and symptoms.

The reason is not that one of the results is wrong. It is that a hormone level answers a narrow question: how much was circulating at the moment the blood was taken. What it cannot answer is what your body did next.

Hormones do not just sit in the blood waiting to be counted. They get used, broken down and cleared, and the machinery doing that runs at different speeds in different people. Blood shows you the hormone itself. The by-products, which come out in urine, show you the route it took.¹ That is the half of the picture a level cannot reach, and it is measured on the same full-day collection that carries the cortisol rhythm, covered separately in our guide to DUTCH test interpretation.

Your body has to clear the estrogen it makes, and it has three exits available. They are not equivalent, because each one produces a different by-product.

The first route produces something mild, with very little hormonal activity left in it. The second produces a by-product that stays biologically busy, closer to a working hormone than a waste product. The third produces something reactive that has to be neutralised properly, because left alone it can damage DNA.² Everyone uses all three. What differs between people is the proportion, and that proportion is what the test reads.

This is worth stating carefully, because it gets oversold. The early research measured only two of the by-products with tests that were not accurate enough, and the results went in all directions.³ Once a method existed that could measure the whole set at once, the picture got clearer. Following a large group of postmenopausal women over years, those whose bodies sent more estrogen down the mild route had a lower rate of breast cancer, and the finding held even after accounting for how much estrogen they made in the first place.⁴ Three long-running studies have now pointed the same way.³

Sending estrogen down the reactive route is not the problem on its own. Your body has a second step that neutralises those by-products and sends them out safely. The problem is when that step runs slowly.

How briskly it runs varies from person to person. Some of that is inherited, through a common variation in the enzyme that does the work.⁵ Some of it is diet, because a number of plant compounds are handled by the same enzyme and compete for it.⁵ Neither is exotic. It is ordinary variation, and most people never find out which side of it they sit on.

The same study that followed those women measured this step directly, and it mattered. Women whose clean-up step was running less completely had a higher rate of breast cancer, again independent of how much estrogen they were producing.⁴ So the test reads two things: which exit your estrogen takes, and whether the riskier exit is being tidied up behind it. A hormone level shows neither.

Testosterone gets converted too, and one of the routes it takes produces DHT, a version several times stronger at the receptor and roughly ten times more powerful at switching on the signal.⁶ The other route produces something far quieter. How much of your testosterone goes each way decides how much androgen effect you actually get from it.

This is how a perfectly normal testosterone result sits alongside obvious androgen symptoms. Male pattern hair loss is driven by what reaches the follicle itself, not by how much testosterone is in the blood, and DHT is doing most of that work.⁷ The same applies to skin and to prostate tissue. A man told his testosterone is fine, while visibly losing hair, is not being told something false. He is being told something incomplete.

Progesterone works the same way. It disappears from the blood quickly, so it is read through its by-products instead, which is a reliable way of seeing how much was actually produced.⁸ One blood draw catches a single moment inside a cycle. The by-products cover the whole day.

Estrogen gets filed as a women’s hormone. It is a convenient shorthand and it costs men real information, because men make estrogen by converting their own testosterone, and it is doing a job.

Researchers proved this cleanly. They took 400 healthy men, switched off their natural hormone production, then gave them testosterone at a range of doses. Half the men also received a drug that blocked the conversion into estrogen, which meant the two hormones could be separated and studied one at a time.⁹

The results split neatly. Losing testosterone cost the men muscle, size and strength. Losing estrogen was what made them gain body fat. Both mattered for libido. So a man whose testosterone reads fine but who is steadily gaining weight around the middle may be looking at the wrong number entirely. The research on the right balance between the two is still developing, and there is no agreed target yet.¹⁰ What is clear is that reading testosterone alone leaves out the hormone it partly turns into.

It maps how your hormones are being handled. It is not a screening test and it does not diagnose disease, and one claim in this field deserves calling out.

The ratio between two of the estrogen by-products has been sold for years as a breast cancer risk score. It is not one. A review of nine studies found the results inconsistent and concluded the evidence does not support using that ratio to predict anything on its own.¹¹ The newer work is more useful precisely because it reads the whole set instead of two members of it. A ratio on a report describes how your body is working. Treating it as a risk score is a misuse of it.

The same discipline applies to changing it. In a placebo-controlled trial, a compound found in broccoli and other cruciferous vegetables clearly shifted the estrogen ratio and raised the protein that binds sex hormones. It also changed nothing about breast density, and it lowered blood levels of a breast cancer drug the women were taking, which matters a great deal to anyone on one.¹² Moving a number is straightforward. Proving that moving it changes how someone does is a much harder claim, and it has not been made.

Breast, prostate and ovarian disease are diagnosed by doctors, with imaging and specialist assessment. When a result points that way, it goes to your GP with a written brief. Used inside those limits, and alongside the cortisol rhythm from the same collection covered in cortisol testing in Australia, the test does the one thing a hormone level cannot: it shows you the route, and the route is where most of the difference between people actually sits.