Subclinical ischaemic episodes during the steady state of sickle cell anaemia.

AIMS: To determine the clinical, haematological, biochemical and rheological changes that occur in the asymptomatic steady state of sickle cell anaemia.
METHODS: Patient self-assessment visual analogue scores (for wellbeing and tiredness), the blood concentration of acute phase proteins (C-reactive protein, orosomucoid, and fibrinogen), and blood rheology (percentage of dense cells and the number of sickled cells that occluded pores 5 microns in diameter) were studied longitudinally on 10 occasions in each of 20 outpatients with sickle cell anaemia.
RESULTS: Patients in the steady state showed fluctuation in visual analogue scores, in concentration of acute phase proteins, and in rheological parameters consistent with minor episodes of tissue injury. Significantly more variation in acute phase proteins occurred in the steady state of 14 of the 20 patients who developed one or more vaso-occlusive crises during the 16 month study period. Rheological fluctuation in the steady state simulated rheological change during crisis, namely a transient rise and then fall in the number of dense and poorly filterable cells.
CONCLUSIONS: The term "steady state" is a misnomer, being characterised by biochemical and rheological fluctuation consistent with minor episodes of microvascular occlusion that are insufficient to cause the overt tissue infarction of painful crisis.