@maine here's the procedure code that was on my EOB when I had the Jak 2 lab done.

81270
JAK2 (Janus kinase 2) (eg, myeloproliferative disorder) gene analysis, p.Val617Phe (V617F) variant

The ICD10 code is D47.3
Essential thrombocythemia (ET): Characterized by high platelets and often a JAK2 mutation

Lab Corp charged $567 for the Lab, but after insurance discount I paid about $100 out of pocket. I'm on a high deductible plan.