Why a full blood count is worth asking for

The association, in plain terms

Myeloproliferative neoplasms are a group of chronic conditions in which bone marrow overproduces blood cells. The most common is polycythaemia vera. They are usually slow-moving and, particularly when found early, manageable for a long time. Most are driven by a mutation in a gene called JAK2.

Itching is a well-recognised feature, and aquagenic itching specifically so. What makes it clinically interesting is the timing:

In that cohort the mean duration of aquagenic pruritus was 6.6 years, and one third of affected patients avoided contact with water altogether.¹ Patients carrying two copies of the JAK2 V617F mutation are reported to show both higher prevalence and greater severity — mast cells and basophils in these patients descend from the same abnormal clone and become hypersensitive to minimal physical stimuli.

There is one further finding worth stating plainly, because it is the real reason not to sit on this. Across observational work in myeloproliferative neoplasms, patients with pruritus — and aquagenic pruritus in particular — show a higher rate of progression to myelofibrosis or acute myeloid leukaemia, and in essential thrombocythaemia aquagenic pruritus has been associated with a higher rate of thrombosis.²³ The authors' conclusion is that pruritus should be assessed in every patient with a myeloproliferative neoplasm. That is an argument for being known to a haematology service and monitored, not an argument for despair.

What to actually ask for

You do not need to arrive with a theory. You need one test and one sentence of context.

1. Ask for a full blood count (FBC, or CBC in the US). Say plainly: I get intense itching after contact with water, with no rash. I have read that this can be associated with myeloproliferative disorders and can precede abnormal blood counts. Could we do a full blood count?
2. The numbers that matter on that result are haemoglobin, haematocrit, red cell count, platelets and white cells. Raised haemoglobin or haematocrit is the classic signal in polycythaemia vera; a raised platelet count matters too.
3. If anything is raised or the picture is suggestive, the next steps are serum erythropoietin and JAK2 V617F mutation testing. These are ordered by a clinician on the strength of the first result — not something to request up front.
4. If everything is normal, that is genuinely reassuring, and it is now on record. Ask what interval would make sense for repeating it, given that the itch can precede the counts.
5. Take the self-check summary with you. Duration, abdominal involvement, spontaneous episodes and washing avoidance are the four features clinicians weigh, and having them written down changes the conversation.

What this is not

Being precise here matters more than being reassuring.

• This is not a cancer screen. A full blood count is not a test for cancer; it is a routine measurement that happens to be abnormal in these conditions.
• Aquagenic pruritus does not cause a blood disorder, and it does not raise your risk of developing one. Where the two occur together, the itch is a symptom of the underlying condition.
• The four features are group-level associations. They describe how populations of patients differed in published studies. They cannot tell you what is happening in your body, and plenty of people with all four have entirely normal counts.
• A normal result does not mean the itch is imaginary. Primary aquagenic pruritus, with no underlying disease, is the more common situation.

Signs that should not wait

Separate from any of the above, these warrant prompt medical assessment on their own:

• Unexplained fatigue, fever, weight loss or night sweats
• Easy bruising, unusual bleeding, or jaundice
• Breathlessness, or headaches with visual disturbance
• Itching that has become generalised over the whole body
• A new episode of itching that appeared in middle age or later without a lifelong history

References

Each figure on this page links to the study it came from, with the sample size shown so you can weigh it yourself. Where a claim rests on a single case report or a self-selected survey, it says so.

1. Aquagenic pruritus in polycythemia vera: clinical characteristics. Acta Dermato-Venereologica. doi:10.2340/00015555-2906 102 patients with molecularly confirmed polycythaemia vera medicaljournals.se ↩
2. Legat FJ. Aquagenic pruritus indicates increased risks in patients with myeloproliferative neoplasms. Journal of the European Academy of Dermatology and Venereology 2023. doi:10.1111/jdv.19107 Commentary on progression and thrombosis risk; full text paywalled onlinelibrary.wiley.com ↩
3. Aquagenic pruritus in essential thrombocythemia is associated with a higher risk of thrombosis. PubMed 31344312 pubmed.ncbi.nlm.nih.gov ↩
4. Le Gall-Ianotto C, et al. Differences between aquagenic and non-aquagenic pruritus in myeloproliferative neoplasms: an observational study of 500 patients. Journal of the European Academy of Dermatology and Venereology 2023;37(6):1175–83. doi:10.1111/jdv.18990 504 patients; 112 with aquagenic pruritus pubmed.ncbi.nlm.nih.gov ↩
5. Witte F, et al. Aquagenic Pruritus Questionnaire: predicting myeloproliferative neoplasms in patients with aquagenic pruritus. Dermatology and Therapy 2025. doi:10.1007/s13555-025-01548-2 Validated in 76 patients with aquagenic pruritus (37 with an MPN) vs 76 controls link.springer.com ↩