Reperfusion, restoring blood flow through thrombolysis (clot-dissolving drug, here intravenous alteplase) or thrombectomy (mechanical clot retrieval), helps only the right patient, so a safety gate stands before every decision to use either. The gate has three questions: is this really stroke, is lysis forbidden, and does the patient fall inside a proven time window.
Rule out mimics first
Severe hypoglycemia can mimic a focal deficit, so glucose is checked and corrected before diagnosing stroke. Blood glucose below 2.7 mmol/L (50 mg/dL) or above 22 mmol/L (400 mg/dL) is a relative contraindication to intravenous thrombolysis. When high clinical suspicion for stroke justifies treatment and a mimic is diagnosed only later, the hemorrhagic risk stays low, with parenchymal hematoma (bleeding into brain tissue) around 1% in registry data.
Contraindications to thrombolysis
Intracranial hemorrhage on imaging is an absolute contraindication to intravenous alteplase. Other findings also exclude treatment:
- Platelet count below 100,000 per mm3, by both guidelines and drug labeling.
- Systolic pressure above 185 or diastolic above 110 mmHg, unless controlled.
- An INR (international normalized ratio, a measure of clotting time) above 1.7.
- Direct thrombin or factor-Xa inhibitor effect, when coagulation labs are not normal.
Single or dual prior antiplatelet therapy does not exclude treatment.
Severity matters as well as safety. For mild non-disabling deficits (NIH Stroke Scale 0–5, the standardized stroke severity score), intravenous alteplase is not recommended. The trial behind this boundary showed no benefit within 3 hours for that severity band.
Extended windows: thrombectomy and wake-up stroke
Mechanical thrombectomy extends the treatable window for large-vessel occlusion beyond thrombolysis alone. For large anterior-circulation occlusion at 6 to 24 hours, selection rests on clinical-imaging mismatch as in the DAWN and DEFUSE-3 criteria. At the time of this review those were the only endorsed late-window selection criteria, and newer eligibility data will need a future update.
Thrombolysis has its own extended case. Wake-up or unknown-onset stroke with diffusion-FLAIR mismatch on MRI can benefit from alteplase within 4.5 hours of recognition. The mismatch marks tissue injured recently enough that lysis still helps.
When imaging shows intracranial hemorrhage, the pathway leaves the ischemic route altogether and turns to haemorrhage care.