Blood donation & hematocrit planner. Know where you sit before the next draw.

How to read this

Hematocrit is the percentage of your blood volume made up of red cells. Testosterone stimulates red-cell production, so a rising hematocrit is a common and expected thing to monitor on therapy — the FDA-approved label for testosterone cypionate directs that haemoglobin and hematocrit be checked periodically during long-term androgen use, and clinical guidelines set out explicit thresholds for prescribers.

What the bands on the gauge mean

• 42–52% is the reference band the TRT AI app displays. It is a display band for orientation, not a clinical cut-off, and your own laboratory’s printed interval is the one that counts.
• Above 52% shows in the upper zone so a rising trend is visible early. It is a prompt to raise the number with your clinician — not an instruction to donate, stop or change anything.
• The 54% figure discussed in the Endocrine Society guideline is a clinician’s decision point, not a target for self-management. It is covered, with sources, in the hematocrit guide.

Donation spacing, and what it is not

US whole-blood collection is limited to no more than once every 56 days (8 weeks) under federal regulation; double red cell apheresis carries a longer deferral, commonly 112 days. This planner does that date arithmetic and nothing more. Meeting the interval is not the same as being eligible to donate — collection centres apply haemoglobin limits and a full health questionnaire on the day.

Voluntary donation and therapeutic phlebotomy are different things: donation exists to supply other patients and is governed by donor-eligibility rules, while therapeutic phlebotomy is a procedure a clinician orders for a documented indication. Which one is appropriate for you — if either — is a clinical question.

How the projection works

Add an earlier reading and the planner fits an ordinary least-squares straight line through your values, then evaluates it at your next eligible date. That is the same simple projection the app runs across your lab history. Its limits are worth stating: two points define a line with no way to detect a curve, hematocrit moves with hydration and altitude as well as with therapy, and a straight line will happily extrapolate somewhere physiologically implausible. It is a direction-of-travel estimate, not a prediction and not a lab result.

Background reading, with primary sources: high hematocrit on TRT and when to draw your panel.