TCD Screening in Sickle Cell Anemia: STOP Criteria (TAMMV)
Sickle cell anemia (SCA) is an exemplary pediatric indication for transcranial Doppler: timely identification of high stroke risk and initiation of transfusion therapy reduces the risk of the first stroke from about 10% per year to less than 1% (according to the STOP study). In cited English sources, the reduction in the frequency of the first stroke is estimated at 90%.
Methodological Feature: Parameter TAMV (TAMM)
In SCA, TAMV (time-averaged mean of the maximum velocity, TAMM) is specifically assessed — the time-averaged mean of the maximum velocity without angle correction, rather than the calculated MFV. The measurement is performed in the MCA and distal (terminal) ICA, as well as according to the protocol in the ACA, PCA, BA, and in the area of intracranial bifurcation bilaterally. This is a separate case from general intracranial assessment — the thresholds are specifically different.
TAMV Thresholds (according to STOP)
| TAMV (MCA / distal ICA) | Interpretation in Sickle Cell Anemia |
|---|---|
| < 170 cm/s | Normal |
| 170–199 cm/s | Conditional result — increased observation |
| ≥ 200 cm/s | Pathology — indication for transfusion therapy to prevent stroke |
High velocities in SCA are a consequence of anemia and vasculopathy, not stenosis (there is an inverse relationship between hematocrit and velocity), so the thresholds differ from general intracranial criteria.
Who and When to Screen
Screening is recommended for children approximately from 2 to 16 years old with an established periodicity (annual TCD is indicated in English sources). Children initially selected by TCD for transfusion should remain on a transfusion regimen to maintain the effect of reducing stroke risk; persistent elevated velocities indicate ongoing stroke risk.
TCD vs TCDI (imaging/nonimaging)
Clinical velocity criteria are validated on nonimaging TCD. When comparing duplex methodology (TCDI) with nonimaging TCD, most studies show slightly lower velocities with TCDI, which is related to the technique of obtaining maximum velocity by color imaging.
Qualification Requirements
Specialists performing these studies must be certified in the STOP methodology before starting work; the skill of testing in children with SCA is taught through standard training modules, and diagnostic criteria for interpreting physicians are clearly defined.
Frequently asked questions
Which parameter is measured in SCA screening — MFV or TAMV?
TAMV (time-averaged mean of the maximum velocity, TAMM) without angle correction, not the calculated MFV. This is a specific case for SCA.
What is the threshold for initiating transfusion therapy?
TAMV ≥ 200 cm/s in the MCA/distal ICA is considered pathological and is an indication for transfusion therapy to prevent stroke (according to STOP).
How to interpret values of 170–199 cm/s?
This is a conditional result requiring increased observation.
At what age is screening indicated?
For children with SCA approximately from 2 to 16 years old with an established periodicity (annual TCD according to English sources).
Why are velocities high in SCA without stenosis?
High velocities are a consequence of anemia and vasculopathy; there is an inverse relationship between hematocrit and velocity, so the thresholds differ from general intracranial ones.