Hyperviscosity refers to any state in which there is increased viscosity of the blood. Increased serum viscosity usually results from increased circulating serum immunoglobulins (eg, macroglobulinaemia, multiple myeloma) and can also result from increased cellular blood components (eg, red or white blood cells) in hyperproliferative states - eg, leukaemias, polycythaemia and thrombocythaemia.1
This is a companion discussion topic for the original article at https://patient.info/doctor/haematology/hyperviscosity-syndrome