Erythropoiesis encompasses all the stages and mechanisms involved in the production of red blood cells, or erythrocytes, under the control of a large number of regulatory agents, most often proteins. Among these proteins, erythropoietin and interleukin-3 play a major role. Similarly, proteins involved in iron metabolism (erythroferrone, hepcidin, ferroportin, transferrin, ferritin) influence erythrocyte production more or less directly. The regulation of erythropoiesis is a fine, complex mechanism involving a large number of players, not only through the stimulation of hypoxia pathways to control erythropoietin synthesis, but also through the availability of iron, an essential element for erythropoiesis. Excessive erythrocyte production can lead to polycythemia, the causes of which are varied, primary or secondary, acquired or constitutional. The aim of this work is the descriptive study (quantitative and/or qualitative) of the various proteins involved in the regulation of erythropoiesis in patients with polycythemia. These proteins will be measured in the plasma of patients obtained after blood sampling or bloodletting (bloodletting being the most common treatment for polyglobulic patients) and will be compared with the proteins of patients without polycythemia.

Inclusion Criteria:

- Persons who have given their non-opposition

Patients with polycythemia:

• haemoglobin value > 16 g/dl female or > 16.5 g/dl male
• with a well-identified cause: either primary (polycythemia Vaquez, erythropoietin receptor or LNK/SH2B3 mutation...) or secondary [cardio-respiratory pathologies, renal pathologies (post-transplant, polycystic kidney disease), metabolic pathologies, tumour (leiomyoma, pheochromocytoma...), constitutional mutations (hyperaffine haemoglobins, HIF2/EPAS1, PHD/EGLN1, VHL, ...)

Patients control:

- persons with a similar pathology to that of polycythemia patients, essentialy secondary, but without polycythemia, i.e. with a haemoglobin value of < 16 g/DL for women and < 16.5 g/DL for men

Exclusion Criteria:

• Person subject to a measure of legal protection (guardianship, tutorship)
• Person subject to a court order
• Pregnant, parturient or nursing woman
• Incapable of expressing consent
• Minor](streamdown:incomplete-link)

Patients with polycythemia