Suggested diagnostic criteria for essential thrombocythemia (ET).
| These criteria are similar to the WHO 2008 criteria but differ in three important respects: |
| 1) Bone marrow histology is not always essential for patients harboring mutations in JAK2 or MPL. |
| 2) Bone marrow histology is not used to subdivide ET into “true-ET” and “prefibrotic myelofibrosis” as the existence of the latter proposed entity remains controversial. |
| 3) This classification includes patients with bone marrow reticulin of greater than grade 2 (on a 0–4 scale) without other features of PMF or myelofibrotic transformation; such patients are not accommodated by WHO 2008 criteria. |
| Diagnosis requires A1-A3 or A1 + A3-A5 |
| A1 Sustained platelet count >450 × 109/L. |
| A2 Presence of an acquired pathogenetic mutation (eg, in JAK2 or MPL). |
| A3 No other myeloid malignancy, especially polycythemia vera (PV), primary myelofibrosis (PMF), chronic myeloid leukemia (CML) or myelodysplastic syndrome (MDS). |
| A4 No reactive cause for thrombocytosis and normal iron stores. |
| A5 Bone marrow trephine histology showing increased megakaryocytes with prominent large hyperlobated forms; reticulin is generally not increased (≤ 2 on a 0–4 scale). |
| These criteria are similar to the WHO 2008 criteria but differ in three important respects: |
| 1) Bone marrow histology is not always essential for patients harboring mutations in JAK2 or MPL. |
| 2) Bone marrow histology is not used to subdivide ET into “true-ET” and “prefibrotic myelofibrosis” as the existence of the latter proposed entity remains controversial. |
| 3) This classification includes patients with bone marrow reticulin of greater than grade 2 (on a 0–4 scale) without other features of PMF or myelofibrotic transformation; such patients are not accommodated by WHO 2008 criteria. |
| Diagnosis requires A1-A3 or A1 + A3-A5 |
| A1 Sustained platelet count >450 × 109/L. |
| A2 Presence of an acquired pathogenetic mutation (eg, in JAK2 or MPL). |
| A3 No other myeloid malignancy, especially polycythemia vera (PV), primary myelofibrosis (PMF), chronic myeloid leukemia (CML) or myelodysplastic syndrome (MDS). |
| A4 No reactive cause for thrombocytosis and normal iron stores. |
| A5 Bone marrow trephine histology showing increased megakaryocytes with prominent large hyperlobated forms; reticulin is generally not increased (≤ 2 on a 0–4 scale). |