ABCD score

Fig. 14.1. Short-term stroke risk stratified by ABCD score in six cohort studies combined (n=4799 patients). Stroke risks are shown at 2, 7, 30 and 90 days (Johnston et a . 2007).

External validation of a model means determining whether it performs well in groups of patients other than those on whom it was derived that is, how is it likely to do in real clinical practice. These other groups almost certainly will differ in case mix, referral patterns, treatment protocols, methods of measurement of variables and definition of outcomes. Nevertheless, if a prognostic model includes powerful predictive variables, appropriately modeled, it should vaUdate reasonably well in other groups of patients. For example. Fig. 14.1 shows the vaUdation of the ABCD score on pooled individual patient data from six independent groups of patients with TIA (Johnston et al. 2007) (Ch. 15). 

These and other factors identified as being associated with early stroke risk (Gladstone et al. 2004 Hill et al. 2004) were used to derive the ABCD score, a predictive tool of stroke risk within seven days after TIA (Rothwell et al. 2005). Briefly, all clinical features that had previously been found to be independently predictive of stroke after TIA were tested in a derivation cohort of 209 patients recruited from the Oxfordshire Community Stroke Project (OCSP, Lovett et al. 2003). Any variable that was a univariate predictor of the seven-day risk of stroke with a significance ofp < 0.1 assessed with the log rank test was incorporated into the score. The score was then validated in three further independent cohorts. 

Although diabetes was found to be predictive of early stroke in the ABCD score (Rothwell et al. 2005), it lacked statistical significance and was not included. However, the ABCD scoring system has been refined in larger cohorts of patients with the subsequent addition of one point for diabetes to make the ABCD score out of 7 (Rothwell et al. 2005 Johnston et al. 2007) (Table 15.3). 

In conclusion, the ABCD and ABCD scores are reliable tools to predict the early risk of stroke after TIA. However, although they are sensitive and easily calculable using clinical information readily available at the time of assessment, they have a high false-positive rate and were deliberately designed to include only clinical data so that they could be used for initial triage. Further information may, therefore, be required to refine risk prediction. 

Giles MF, Rothwell PM (2008). Systematic review and meta-analysis of validations of the ABCD and ABCD scores in prediction of stroke risk after transient ischaemic attack. Cerebrovascular Diseases, in press... 

Purroy F, Molina CA, Montaner J, Alvarez-Sabin J (2007). Absence of usefulness of ABCD score in the early risk of stroke of transient ischemic attack patients. Stroke 38 855-856 Rantner B, Pavelka M, Posch L (2005). Carotid endarterectomy after ischemic stroke is there a justification for delayed surgery European Journal of Vascular Endovascular Surgery 30 36-40... 

The study recorded the medical history, medications, symptom details, examination findings, final diagnosis, treatment plans and one-year outcomes (assessed by phone calls) of all referrals. In the first report of all 629 consecutive patients with definite TIA seen from January 2003 to December 2005, there were three strokes within seven days and 12 strokes within three months of follow-up, giving risks of 0.3% and 1.9%, respectively. The expected risk of stroke at three months as calculated by the ABCD score (Johnston et al. 2007) was 6%. Although there was no formal comparison arm of the study, the considerable reduction in observed rates of stroke compared with those expected by the ABCD score was reasonably attributed to urgent access to and treatment in a dedicated specialist neurovascular unit. However, it should be noted that this study only assessed stroke risk among patients referred to the clinic and not all those within the population. 

Table 15.2. The clinical features and scoring for the ABCD system of assessing risk of stroke in the seven days after a transient ischemic attack...

Table 15.3. The clinical features and scoring for the ABCD system...

Lancet 363 1925-1933 Rothwell PM, Giles MF, Flossman E et al. (2005). A simple score (ABCD) to identify individuals at high early risk of stroke... 

FIGURE 6.2 In vivo titration of blood AChE in rhesus monkeys pretreated with 105 nmoles of FBS AChE (ABCD). Soman dose shown is the cumulative LDjq. Percent correct responses and response latencies for rhesus monkeys. SPR scores (list length of one item) were obtained at indicated times before administration of 105 nmoles of FBS AChE and after challenge with... 

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