Stroke in children with sickle cell disease (SCD) is associated with significant morbidity and mortality. Transcranial Doppler (TCD) velocities, specifically time-averaged maximum mean velocity (TAMMV), are critical for stroke risk stratification. Variability in TCD velocity measurements across different machines and ultrasonographers complicates clinical decision-making. Using a phantom Doppler flow machine generating a fixed flow, we evaluated four non-imaging and one imaging TCD machine against a reference TAMMV of 191 cm/s. All machines demonstrated high precision but varied accuracy, with mean velocities ranging from 169 to 189 cm/s. All non-imaging machines underestimated the TAMMV (p <
0.001). The imaging TCD machine also underestimated the velocity, even after a standard adjustment of adding 15 cm/s to the velocity (p <
0.001). Based on the results of the local non-imaging TCD machines accuracy, the northern Nigerian pediatricians agreed on the following threshold for primary stroke prevention for all non-imaging TCD machines: two independent ultrasonographers' velocities for any velocity ≥ 180 cm/sec and <
220 cm/sec or one TCD velocity >
200 cm/sec.