How does the ASTRAL (Astral Stroke Risk Assessment Tool) compare to the iScore (ischemic stroke predictive risk score) for predicting stroke outcomes?

ASTRAL vs iScore for Predicting Stroke Outcomes

The ASTRAL score demonstrates superior prognostic accuracy compared to iScore for predicting functional outcomes after acute ischemic stroke, with the highest area under the receiver operating characteristic curve (AUROC 0.78-0.79) among validated stroke prediction tools. 1

Direct Comparative Performance

Head-to-head validation using the Virtual International Stroke Trials Archive (VISTA) dataset of 10,777 patients definitively established ASTRAL as the most accurate prognostic tool, outperforming iScore and six other stroke prediction scales for predicting 90-day modified Rankin Scale (mRS) outcomes. 1

Key Performance Metrics:

• ASTRAL achieved AUROC 0.78-0.79 for predicting poor functional outcomes (mRS >2), significantly superior to all other scales on formal comparative testing 1
• iScore demonstrated AUROC 0.86 for poor functional outcomes in the same validation cohort, performing well but statistically inferior to ASTRAL 1
• Both tools showed comparable performance for mortality prediction (AUROC 0.87-0.88), with no significant difference between them 2, 1

Clinical Context and Appropriate Use

When ASTRAL Performs Best:

• ASTRAL is the preferred tool for general stroke outcome prediction across diverse patient populations, as it demonstrated the highest discrimination across multiple outcome measures 1
• The tool maintains accuracy for both functional outcomes and mortality prediction in real-world clinical settings 2

When iScore Provides Specific Value:

• iScore is particularly useful for stratifying patients being considered for thrombolysis, as it identifies those most likely to benefit from tissue plasminogen activator (tPA) treatment 3
• Patients with iScore <200 showed 47% higher odds of favorable outcomes with tPA (OR 1.47,95% CI 1.30-1.67), while those with iScore ≥200 showed no significant benefit 3
• iScore can be simplified by substituting TOAST stroke subtype classification with the more readily available Oxfordshire Community Stroke Project (OCSP) classification without loss of predictive accuracy (revised iScore AUROC 0.767-0.801) 4

Practical Implementation Algorithm

For General Stroke Prognosis:

1. Use ASTRAL as the primary prediction tool for estimating functional outcomes at 90 days in all acute ischemic stroke patients 1
2. Calculate ASTRAL score incorporating age, stroke severity (NIHSS), time from onset, visual field defects, acute glucose, and level of consciousness 1

For Treatment Decision-Making:

1. Calculate iScore when considering thrombolytic therapy to identify patients most likely to benefit (target iScore <200) 3
2. Use iScore cutoff of ≥200 to identify patients with very poor prognosis where aggressive interventions may have limited benefit 3

For Resource-Limited Settings:

1. Consider the revised iScore using OCSP classification when extensive stroke subtyping investigations are not immediately available 4
2. This maintains predictive accuracy (AUROC 0.767-0.801) while requiring fewer diagnostic resources 4

Important Limitations and Caveats

Accuracy Constraints:

• Even ASTRAL's prognostic accuracy (AUROC 0.78-0.79) may not be sufficient as the sole basis for major clinical decisions such as withdrawal of life-sustaining treatment 1
• Both tools should be interpreted within the complete clinical context rather than used as standalone decision-making instruments 5

Validation Gaps:

• Neither tool has been adequately validated across all age, sex, and racial-ethnic groups, limiting generalizability in diverse populations 6, 5
• Current risk stratification schemes ignore clinically important outcomes including functional decline, disability progression, and dementia 7, 8

Specific Clinical Scenarios:

• Neither ASTRAL nor iScore is designed for large vessel occlusion detection—use NIHSS, RACE, LAMS, or CPSSS instead for this purpose 7, 8
• Both tools perform better when calculated after 24 hours from symptom onset rather than at initial presentation 9

Comparative Advantage Summary

ASTRAL provides superior overall prognostic accuracy and should be the default choice for outcome prediction in acute ischemic stroke. 1 However, iScore offers specific advantages for treatment stratification, particularly identifying patients who will benefit from thrombolysis, and can be simplified for resource-limited settings without significant loss of accuracy. 3, 4 The choice between tools should be guided by the specific clinical question: use ASTRAL for general prognosis and iScore for treatment-specific risk stratification.