An acute stroke occurs when blood flow to the brain is blocked or a blood vessel ruptures, causing brain cells to die rapidly. A transient ischemic attack (TIA), often called a mini-stroke, involves temporary symptoms from a brief blockage without permanent brain damage. Rapid brain imaging, typically a CT or MRI scan, is the definitive method for distinguishing between an ischemic stroke (clot) and a hemorrhagic stroke (bleed). While blood tests do not diagnose stroke directly, they are a vital component of the overall assessment, supporting the diagnosis, ruling out mimic conditions, and guiding immediate treatment.
Standard Blood Tests During Emergency Assessment
When a patient arrives with suspected stroke symptoms, standard blood tests are urgently performed to ensure stability and prepare for treatment. Blood glucose levels are tested immediately to rule out hypoglycemia (very low blood sugar), which can mimic stroke symptoms like weakness and confusion. Electrolyte balance and kidney function tests are also performed to identify metabolic disturbances that may affect how certain medications are processed.
A Complete Blood Count (CBC) provides information on red blood cells, white blood cells, and platelets. This test helps assess for anemia, infection, or counts that contribute to clotting problems or bleeding risk. The coagulation panel, including Prothrombin Time (PT), International Normalized Ratio (INR), and Activated Partial Thromboplastin Time (aPTT), is essential for guiding treatment. These tests measure how quickly the blood clots, which is required before administering thrombolytics (clot-busting medications) to ensure the patient does not have a pre-existing bleeding disorder.
Novel Biomarkers for Acute Stroke Detection
While standard blood tests serve a supportive role, research focuses on identifying specific proteins, or biomarkers, released into the bloodstream following brain injury. The goal is to develop a rapid, portable test that first responders could use to confirm a stroke and determine its type before hospital arrival. Such a test would accelerate time-sensitive treatments like endovascular thrombectomy.
One of the most promising novel biomarkers is Glial Fibrillary Acidic Protein (GFAP), released from astrocytes when the brain is damaged. GFAP is valuable because it is highly elevated in hemorrhagic stroke (a bleed) but remains low or undetectable in most ischemic stroke cases (a clot). High GFAP levels quickly alert clinicians to a bleed, preventing the administration of clot-busting drugs that could worsen a hemorrhage. Combining GFAP with other assessments has shown high accuracy in identifying patients with large vessel occlusion (LVO) strokes in clinical studies.
Another biomarker of interest is S100B, a protein predominantly found in glial and Schwann cells. Like GFAP, S100B is released into circulation when the blood-brain barrier is compromised, marking brain tissue damage. Elevated S100B levels correlate with infarct size and poorer long-term functional outcomes following a stroke. However, its use as a definitive diagnostic tool is limited because its levels can also rise in response to trauma outside the brain, lacking the specificity needed for widespread clinical adoption.
The D-dimer protein is another frequently studied acute marker, produced when a blood clot is broken down in the body. While not specific to the brain, D-dimer levels are often elevated in stroke patients, especially those with a large clot causing the blockage. Combining D-dimer with GFAP is a promising research strategy to improve early detection and classification. High D-dimer levels combined with a low GFAP reading strongly suggest an ischemic event, offering a rapid way to differentiate the two primary stroke types. These acute biomarkers are not yet standard emergency care, but their potential for rapid triage drives ongoing clinical trials.
Blood Markers Used in Long-Term Risk Prediction
Beyond the immediate emergency, blood tests play a significant role in assessing and managing a patient’s long-term risk for a future stroke or TIA. This preventative analysis focuses on underlying chronic conditions that predispose an individual to vascular disease. A primary set of tests involves the detailed lipid panel, which measures cholesterol fractions.
The lipid panel provides specific values for total cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL), and triglycerides. High levels of LDL-C (“bad cholesterol”) contribute to atherosclerosis, the buildup of fatty plaques in the arteries, which causes ischemic stroke. Conversely, higher levels of HDL-C (“good cholesterol”) are associated with a reduced risk because this fraction helps remove excess cholesterol.
Another important marker for long-term risk is Hemoglobin A1c (HbA1c), which measures a patient’s average blood sugar control over the previous two to three months. Poorly controlled diabetes, indicated by a high HbA1c, significantly increases stroke risk due to the damage high glucose levels inflict on blood vessel walls over time. Monitoring HbA1c is therefore a routine part of stroke prevention and management for diabetic patients.
Chronic inflammation, which destabilizes plaques and promotes clotting, is assessed using high-sensitivity C-reactive protein (hs-CRP). This marker indicates low-grade, systemic inflammation, which is an independent predictor of stroke risk, even after accounting for traditional factors like cholesterol and blood pressure. A high hs-CRP reading suggests a person may benefit from more aggressive preventative treatment, as inflammation contributes to the development of atherosclerosis.