Situation: A 64-year-old woman is brought to a stroke-ready hospital with sudden right-sided weakness and slurred speech that began 90 minutes ago. She weighs 104 kg. Noncontrast computed tomography (CT) shows no hemorrhage, and the team plans intravenous (IV) alteplase for acute ischemic stroke. While the alteplase is being prepared, the rest of her history and results come back. Which finding excludes her from thrombolysis?

Alteplase is contraindicated with a platelet count below 100,000/mm³ (100 × 10⁹/L), an INR above 1.7, or an ischemic stroke within the past 3 months. Her platelet count of 85,000/mm³ is below the limit. An INR of 1.5, a stroke 5 months ago, and daily aspirin do not exclude her.

Why platelet count is the exclusion criterion

Alteplase works by converting plasminogen to plasmin, which degrades fibrin clots. The same fibrinolytic action also increases the risk of intracranial hemorrhage, and that risk depends heavily on the patient’s hemostatic reserve. A platelet count below 100,000/mm³ (100 × 10⁹/L) is a standard exclusion for IV alteplase in acute ischemic stroke because platelets provide the first line of vascular repair at sites of endothelial injury and microhemorrhage ^[1][4]. When platelets are depleted, even small vessel leaks that normally seal spontaneously can expand into symptomatic bleeding.

Thrombocytopenia is not merely a laboratory abnormality; it directly removes a major protective mechanism against alteplase-induced hemorrhagic transformation. The case report by Bragin and Chen explicitly identifies a platelet count below 100,000/mm³ as a contraindication to IV thrombolysis for acute ischemic stroke ^[4]. In the registry study by Xu et al., severe thrombocytopenia was defined as a pre-thrombolysis platelet count below 100 × 10⁹/L, and this group was analyzed separately from patients with mild thrombocytopenia or normal counts ^[1]. The patient’s value of 85,000/mm³ (85 × 10⁹/L) falls into that severe category, so the team must withhold alteplase regardless of the otherwise favorable time window.

Why the other options do not exclude her

Finding	Why it is acceptable	Threshold that would exclude
Ischemic stroke 5 months ago with full recovery	The exclusion applies to ischemic stroke within the past 3 months. Five months is beyond that window, and full recovery further lowers concern for recurrent bleeding into the old infarct.	Ischemic stroke within 3 months
INR of 1.5	An INR of 1.5 is only mildly elevated and does not indicate clinically significant anticoagulation. It remains below the exclusion threshold.	INR above 1.7
Aspirin 80 mg taken this morning	Single antiplatelet therapy with low-dose aspirin is not an exclusion for IV alteplase. The benefit of reperfusion outweighs the modest additional bleeding risk from one antiplatelet agent.	Not excluded by aspirin alone; caution applies with dual antiplatelet therapy or full-dose anticoagulation

Pathophysiology of the platelet threshold

During alteplase infusion, plasmin degrades not only pathologic thrombus but also protective hemostatic plugs. Platelets adhere to exposed subendothelial collagen at sites of microvascular injury, aggregate, and provide a phospholipid surface for coagulation factor assembly. When the platelet count drops below 100,000/mm³, this primary hemostatic response becomes inadequate, and the fibrinolytic effect of alteplase can convert a clinically silent microhemorrhage into a large parenchymal hematoma ^[4]. The Delphi study by Dirks et al. reinforces that trial-derived exclusion criteria, including severe thrombocytopenia, are retained as clinical contraindications because specialists recognize the unacceptable bleeding risk in real-world settings .

The platelet threshold is a safety gate: it identifies patients whose baseline hemostatic reserve is too low to tolerate pharmacologic fibrinolysis. Even though the patient presents within the 90-minute window and CT shows no hemorrhage, the laboratory value alone disqualifies her from IV alteplase.

Clinical application and nursing priority

The nursing priority is to recognize that a platelet count of 85,000/mm³ is an absolute contraindication and to communicate this finding immediately to the stroke team before alteplase is administered. Do not wait for the infusion to be prepared; the order should be cancelled or held based on this result. The patient may still be evaluated for mechanical thrombectomy if large-vessel occlusion is present, because endovascular retrieval does not carry the same systemic fibrinolytic bleeding risk as IV alteplase.

Watch out! A common error is to focus on the time window or CT result and overlook the platelet count. The time window is favorable and the CT is negative, but the platelet count alone is sufficient to exclude thrombolysis.

Key point! The three laboratory exclusions to memorize for IV alteplase in acute ischemic stroke are platelet count below 100,000/mm³, INR above 1.7, and elevated activated partial thromboplastin time above the upper limit of normal. A platelet count of 85,000/mm³ crosses the first threshold and mandates withholding alteplase ^[1][4].