Activated Partial Thromboplastin Time
Haematology marker
APTT
Activated Partial Thromboplastin Time
Measures the time for blood to clot via the intrinsic and common coagulation pathways. Used to screen for clotting factor deficiencies and to monitor unfractionated heparin therapy.
PED Notes
APTT itself is not a routine PED monitoring test, but coagulation matters for enhanced athletes. Androgens (testosterone and other AAS) drive erythropoiesis, and the resulting rise in haematocrit thickens the blood and raises thrombotic risk independent of any clotting-time change. AAS also shift the haemostatic balance toward a prothrombotic state (altered fibrinolysis, platelet activation, and changes in clotting factor and antithrombin levels), so a normal APTT does NOT mean clot risk is low if haematocrit is high. APTT is the standard test used to monitor unfractionated heparin if anticoagulation is ever required. No PED shifts the healthy target range, so the bodybuilder reference range equals the standard range.
When high
When prolonged (>38 seconds):
- A prolonged APTT means the intrinsic pathway is slow to clot. Common causes: heparin therapy, clotting factor deficiencies (VIII, IX, XI, XII), von Willebrand disease, liver disease reducing factor synthesis, or a lupus anticoagulant (which paradoxically raises clot risk despite the prolonged time).
- What to do: repeat with a mixing study to distinguish factor deficiency from an inhibitor. Review any anticoagulant or heparin exposure.
- Liver stress from oral 17-alpha-alkylated AAS can impair clotting factor synthesis; if the APTT is prolonged alongside elevated ALT/AST and bilirubin, treat the liver (see the ALT and bilirubin markers) and recheck.
- Do not start or stop any anticoagulant without physician oversight.
When low
When shortened (<25 seconds):
- A short APTT usually reflects an acute-phase reaction or a hypercoagulable (pro-clotting) state, and in enhanced athletes should prompt a look at haematocrit and overall thrombotic risk rather than reassurance.
- What to do: check full blood count and haematocrit. If haematocrit is high on TRT/AAS, address that (see the Haematocrit marker: hydration, dose reduction, or therapeutic phlebotomy) because polycythaemia is the dominant clot driver.
History Chart
Reading History
Frequently Asked Questions
Reference Ranges
Standard Range
VitalMetrics Range