Peak and Trough

Peak and trough are the highest and lowest hormone levels between two doses. The peak comes a while after a dose goes in; the trough is just before the next one. How far apart they are depends on the medicine, the form it takes and how often it is given.

Where you'll meet it

When a prescriber or phlebotomist asks when you last took your dose before a blood test. In forum threads about injection schedules, where people describe levels "crashing" before the next shot. And on lab request forms, where a clinic may ask for a "trough level" specifically.

What it means for you

Every form of hormone therapy produces a curve rather than a flat line. After a dose, the level in your blood climbs to a high point, then falls as your body clears it, until the next dose pushes it back up. A single blood result is one point on that curve.

That is why a level only means something if you know where in the cycle it was taken. The same person can look very high a day or two after an injection and low the day before the next one, with nothing wrong at all. Comparing a peak result with a trough result from six months earlier can make it look as though something has changed when only the timing has.

Which forms swing most

• Short-acting injections swing the most, and the longer the gap between doses, the wider the swing. A larger dose every two weeks gives a higher peak and a lower trough than the same total split into weekly injections.
• Tablets peak within hours of each dose. Tablets dissolved under the tongue rise and fall faster still.
• Long-acting injections such as testosterone undecanoate change slowly over weeks, so they sit between short-acting injections and the flattest forms.
• Gels and patches, the transdermal forms, give the steadiest levels, with no peak and trough in the injection sense.

How it is measured

Many prescribers ask for trough levels, taken just before a dose, because they are the easiest to compare over time and show whether you are dropping too low. Others want a mid-cycle figure, closer to your average. There is no universal rule, and clinics differ. What matters is that the timing is agreed and kept the same every time, and that whoever reads the result knows when your last dose was. How to read your hormone blood results goes through timing for each form, along with units and targets.

Why the swing matters beyond the number

Some people feel the trough: tiredness, low mood, irritability, hot flushes on feminizing hormones, or spotting on testosterone as levels dip. Some feel the peak too, as restlessness or, on testosterone, a burst of oily skin. These are worth telling your prescriber about rather than putting up with, because a shorter interval between doses or a different form can flatten the curve. Testosterone and estrogen describe how the forms compare.

Common questions

"A high result means my dose is too high." Not if the blood was taken at the peak. Check the timing first.

"A low result means I should take more." Not if it was a trough. A single odd number is often a timing problem, and the fix is usually a repeat test, not a dose change you make yourself.

What to ask

Ask whether your prescriber wants the test at trough, peak or mid-cycle, and exactly how many hours or days after your dose that is. Note the time of your last dose on your own copy of every result.

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