If you are being evaluated for stroke, it is likely that your doctor will order some blood tests. Stroke cannot be diagnosed by a blood test alone. However, these tests can provide information about stroke risk factors and other medical problems which may be important.
Please note that the first set of tests are commonly used for routine or emergency evaluation of stroke, while the others are used only in very specific situations. Unless otherwise noted, each of these tests require just one tube of blood (a few teaspoons) drawn from a vein.
Commonly Used Blood Tests
- CBC (Complete blood count)
This is a routine test to determine the number of red blood cells, white blood cells, and platelets in your blood. Hematocrit and hemoglobin are measures of the number of red blood cells. A complete blood count might be used to diagnose anemia (too little blood) or infection (shown by too many white blood cells).
- Coagulation tests
PT (Prothrombin time)
PTT (Partial thromboplastin time)
INR (International normalized ratio)
These tests measure how quickly your blood clots. An abnormality could result in excessive bleeding or excessive clotting (which is difficult to measure). If you have been prescribed a blood-thinning medicine such as warfarin (Coumadin or similar drugs), the INR is used to be sure that you receive the correct dose. It is very important that you obtain regular checks. If you are taking heparin, the PTT (or aPTT) test is used to determine the correct dose.
- Blood chemistry tests
These tests measure the levels of normal chemical substances in your blood. The most important test in emergency stroke evaluation is glucose (or blood sugar), because levels of blood glucose which are too high or too low can cause symptoms which may be mistaken for stroke. A fasting blood glucose is used to help in the diagnosis of diabetes, which is a risk factor for stroke. Other blood chemistry tests measure serum electrolytes, the normal ions in your blood (sodium, potassium, calcium) or check the function of your liver or kidneys.
- Blood lipid tests
Cholesterol, total lipids, HDL, and LDL
Elevated cholesterol (particularly “bad” cholesterol, or LDL) is a risk factor for heart disease and stroke. More information about cholesterol and cardiovascular risks is available from the National Institutes of Health.
Blood Tests for Specific Situations
This is a partial list of less common blood tests sometimes ordered for specific stroke situations, or where the cause of stroke is unclear (for example, in a young person without known stroke risk factors). Abnormal results may suggest a cause for the stroke.
- Antinuclear antibodies (ANA)
- Antiphospholipid antibodies (APL), Anticardiolipin antibodies (ACL), Lupus anticoagulant (LA)
- Blood culture
- Cardiac enzymes: Troponin, Creatine kinase (CPK, CK), LDH isoenzymes
- Coagulation factors: Antithrombin III, Protein C, Protein S; Factor VIII; activated Protein C resistance (Factor V Leiden)
- Erythrocyte sedimentation rate (ESR)
- Hemoglobin electrophoresis
- Syphilis serology (VDRL, FTA, others)
- Toxicology screen (serum or urine)
Please note that this chart applies only to the use of these tests for stroke diagnosis. Be sure to discuss any questions or concerns with your doctor or health care provider.