CPT code 81279 describes a laboratory molecular test that analyzes specific sequences of the JAK2 (Janus kinase 2) gene — for example, sequencing of exons 12 and 13 — performed on a patient specimen (such as blood) to detect variants associated with myeloproliferative neoplasms in patients who are negative for the JAK2 V617F mutation; service type: molecular pathology / gene sequencing; typical site of service: clinical molecular laboratory or hospital laboratory performing diagnostic gene sequencing on collected specimens.