Normal Counts, High Risk: Abdul Mannan Breaks Down JAK2 + Splanchnic Vein Thrombosis
Abdul Mannan, Consultant Haematologist at Betsi Cadwaladr University Health Board, posted on LinkedIn:
”You find JAK2V617F in a patient with splanchnic vein thrombosis. Counts are normal. The marrow doesn’t show MPN. Now what?
Here’s the thing: JAK2 positivity in SVT means clonal, persistent risk. It doesn’t disappear just because the blood count looks normal.
Here’s what the evidence tells us:
• JAK2+ SVT behaves as a chronic prothrombotic state, even without overt MPN on counts or marrow
• Budd-Chiari syndrome should get indefinite anticoagulation from the start (target INR 2-3 with LMWH or VKA )
• Portal or mesenteric vein thrombosis with JAK2 positivity usually needs extended or indefinite anticoagulation, tailored to bleeding risk
• Ruxolitinib (Jakavi) is NOT standard for thrombosis prevention alone – it may help if an overt MPN later declares itself, but it doesn’t replace anticoagulation
• Cytoreduction isn’t indicated when counts are truly normal
Here’s what matters for follow-up: some patients do progress to overt MPN over time. One cohort had 30% declare MPN at a median of 41 months. So you’re looking at periodic CBCs, iron studies if polycythemia concerns you, and keeping step with hepatology for varices and bleeding risk.
The lesson for clinic: don’t withhold anticoagulation waiting for “diagnostic” marrow features, and don’t reach for ruxolitinib to avoid anticoagulation. Both are misses.
What’s your approach when JAK2 shows up in unusual thrombosis?”
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