The significance of inadequate transcranial Doppler studies in children with sickle cell disease.

Sickle cell disease (SCD) is a common cause of cerebrovascular disease in childhood. Primary stroke prevention is effective using transcranial Doppler (TCD) scans to measure intracranial blood velocities, and regular blood transfusions or hydroxycarbamide when these are abnormal. Inadequate TCD scans occur when it is not possible to measure velocities in all the main arteries. We have investigated the prevalence and significance of this in a retrospective audit of 3915 TCD scans in 1191 children, performed between 2008 and 2015. 79% scans were normal, 6.4% conditional, 2.8% abnormal and 12% inadequate. 21.6% of 1191 patients had an inadequate scan at least once. The median age of first inadequate scan was 3.3 years (0.7-19.4), with a U-shaped frequency distribution with age: 28% aged 2-3 years, 3.5% age 10 years, 25% age 16 years. In young children reduced compliance was the main reason for inadequate TCDs, whereas in older children it was due to a poor temporal ultrasound window. The prevalence of inadequate TCD was 8% in the main Vascular Laboratory at King's College Hospital and significantly higher at 16% in the outreach clinics (P<0.0001), probably due to the use of a portable ultrasound machine. Inadequate TCD scans were not associated with underlying cerebrovascular disease.