Key inclusion criteria were a negative test for JAK2 V617F between 1 January 2014 and 31 December 2018; no diagnosis of myeloproliferative neoplasm; no prior investigation for myeloproliferative neoplasm; Hb or Hct above the WHO thresholds for polycythaemia. The gene discussed is JAK2; the disease is myeloproliferative disorder.