Essential Thrombocythemia: A Risk Score That May Not Be Asking About Her Real Risk
A single patient with newly diagnosed essential thrombocythemia who scores low risk on the standard thrombosis model. The disagreement isn't about the model's arithmetic — it's about what that model doesn't ask her.
S.K., a 45-year-old high school chemistry teacher, learned about her platelet count the way many ET patients do: an incidental finding on labs drawn for something unrelated, this time a pre-surgical workup for a knee scope. The count came back at 1,650,000 — high enough that the number stops being a degree of abnormality and becomes a finding in its own right, since above roughly a million and a half circulating platelets begin adsorbing enough high-molecular-weight von Willebrand multimers to functionally deplete them, and a disease everyone files under clotting starts producing bleeding instead. A bone marrow biopsy confirmed essential thrombocythemia and molecular testing returned JAK2 V617F. She has never had a clot. By IPSET-thrombosis, which sorts patients on age, JAK2 status and prior thrombosis and on nothing else at all, being 45 with a positive mutation and no prior event puts her in the lowest tier — aspirin alone, not the tier where cytoreduction is automatic.
Her chart holds two things the score never asks her about. She has smoked half a pack a day for fifteen years and her blood pressure has been indifferently controlled on lisinopril — ordinary cardiovascular risk factors, which observational data in ET associates with thrombosis independently of the formal category, and which the model was simply not constructed to weigh. Her platelet count is the second, and it points the opposite way from everything else in the conversation: the same extremity that makes the team want to lower it is the extremity that may already be causing an acquired bleeding disorder. A ristocetin cofactor activity has not been drawn. Until it is, nobody in the room knows whether the low-dose aspirin she is already taking — standard, uncontroversial, the default for low-risk ET — is protecting her or is the single most likely thing to make her bleed.
Hematology clinic, risk-stratification review
IPSET-thrombosis puts her in the low-risk tier, and that's not an arbitrary cutoff — it reflects where the randomized evidence for cytoreduction's benefit actually sits. Starting hydroxyurea in a 45-year-old at low formal risk commits her to a drug with a real, if debated, long-term leukemogenic signal, for a benefit that hasn't been validated at her risk tier specifically.
I take the score seriously, but it has a real blind spot: it doesn't ask about hypertension or smoking at all, despite observational data linking both to elevated thrombotic risk in ET independent of the formal category. And 1.65 million isn't just a number sitting comfortably inside 'low risk' — it's high enough that I'd want her actual risk read as higher than the score alone suggests.
'Not validated by a randomized trial at her tier' isn't the same as 'no benefit' — it's an evidence gap the score's own scope created, not a finding against treating her.
Before either of you finalizes a cytoreduction-timing position, I'd want ristocetin cofactor activity drawn. At platelet counts this extreme, acquired von Willebrand syndrome is a real, testable possibility — and it would matter to both of your arguments: it would raise the urgency of lowering her platelet count regardless of the IPSET debate, and it would mean starting aspirin, which is otherwise standard even at low risk, needs to wait for that result first.
Agreed: start hydroxyurea now rather than waiting for a formal high-risk reclassification, treating her combined risk-factor burden as sufficient grounds to act ahead of the score; hold aspirin pending the ristocetin cofactor result.
Left as a genuinely open question, not resolved by today's decision: at what point does starting a 45-year-old on decades of a therapy meant for higher-risk patients stop being reasonable extrapolation and become treating a risk score rather than a patient? The hematologist-oncologist's caution about the exposure ahead of her wasn't answered today, only outweighed by her combined risk-factor burden as it stands right now — revisit in full if her cardiovascular risk factors come under control and her platelet count responds.