Tracking TRT: esters, timing and bloodwork

Testosterone replacement therapy is unusual among the protocols in this app: it is adjusted from a measurement. Every few months a blood test produces a number, and that number decides whether the dose stays put. Which makes one detail enormously important and almost always unrecorded: when in the cycle the blood was drawn.

The ester decides the shape of your week

Injected testosterone is esterified so that it releases slowly from the injection site. The ester is what sets the half-life, and therefore how much the level swings between injections.

This is the whole reason "split your dose" is such a common piece of advice: injecting half as much twice as often does not change the weekly total, but it halves the distance between peak and trough. Whether that is worth doing is a clinical question. What is not a question is that it changes what a blood test taken on a Friday means.

Trough labs, and why the date of the draw is the point

Labs for TRT are usually drawn at trough, immediately before the next injection when the level is at its lowest, precisely because it is the one moment in the week that is reproducible. A sample taken two days after an injection and compared against a previous one taken six days after tells you almost nothing about whether anything has changed.

Half-life also sets how soon after a change it is worth testing at all. At roughly eight days for cypionate, five half-lives is about six weeks: test before that and you are measuring the climb rather than the plateau. The arithmetic behind that is in peptide half-life, explained.

What is worth recording between appointments

• Every injection: date, dose in milligrams, ester, and site. Sites matter here as much as anywhere: these are frequent, long-running injections into a small number of places. See injection site rotation.
• Anything else in the protocol, on its own schedule: hCG, an aromatase inhibitor, a SERM. They have their own frequencies and their own reasons, and a lab result read without them is missing half the picture.
• Labs, in full. Total and free testosterone, oestradiol, haematocrit, PSA where relevant, whatever your clinician ordered, with dates. A trend across four draws is worth more than any single panel.
• Subjective measures, on a fixed cadence. Energy, sleep, libido, mood, training. These are why people are on TRT, and they are the first thing that gets rewritten by memory.

The pattern that a record makes visible

Two examples that come up constantly and are invisible without dates. The first: someone feels flat in the last two days before an injection, and the fix under discussion is a dose increase, when what the record shows is a trough problem that splitting the same weekly dose would address. The second: a lab result comes back much higher than the last one, and the difference is not the dose at all but a draw taken on day two instead of day seven.

Neither is something an app decides. Both are things a clinician can only see if the dates are written down, which is the entire argument for keeping the log at all.