How I read biology

Cortisol follows a timed daily shape rather than holding a level. Because the same value can be typical at one hour and unusual at another, a single reading carries limited information without the time it was taken and the time you woke.

Haemoglobin measures iron currently in circulation. Ferritin estimates what is held in reserve. Reserves can run low well before circulating levels fall, which is one reason a standard blood count can come back unremarkable while symptoms persist.

A small sustained rise in waking temperature usually follows ovulation rather than predicting it. It tends to confirm what already happened, which makes it useful for reading a cycle backwards but unreliable for timing anything forwards.