ET PT-1 risk stratification
Essential thrombocythaemia risk groups, as defined in MRC PT-1 trial
|Risk group||Age (years)||High risk features*|
|Intermediate||40 - 60||Absent|
|High||> 60, OR at least one high risk feature||At least one, OR age > 60|
- Platelet count ≥ 1500 x109/L (current or previous)**
- History of ischaemia, thrombosis or embolic events (including erythromelalgia)
- Haemorrhage considered to be related to essential thrombocythemia
- Presence of hypertension or diabetes requiring treatment
** if a borderline platelet count is the sole reason for allocation to a high-risk group, requires at least three separate blood count results taken over at least 2 months
This risk stratification system for essential thrombocythemia (ET or PT; also known as primary thrombocythemia, or primary or essential thrombocytosis) is that used in the Medical Research Council PT-1 clinical trial.1 The criteria for allocation of patients to the high-risk group is similar to that proposed by other groups, but there is less consensus on the criteria for low- and intermediate-risk groups.2
In the PT-1 trial, low-risk patients received aspirin alone. High-risk patients received aspirin and cytoreductive therapy. Intermediate-risk patients were randomised between aspirin alone or aspirin with cytoreductive therapy.3
- PT-1 Trial Protocol Version 5.0. Accessed 27 March 2015.
- Harrison CN. Essential thrombocythaemia: challenges and evidence-based management. Br J Haematol. 2005; 130: 153-65.
- Harrison CN, Campbell PJ, Buck G, Wheatley K, East CL, Bareford D et al. Hydroxyurea compared with anagrelide in high-risk essential thrombocythemia. NEJM 2005; 353: 33-45.