There is no blood test that can diagnose a stroke on its own. If you are being evaluated for a stroke or transient ischemic attack (TIA), your doctor will order blood tests to provide general information about your health and clues to what may have caused your stroke or stroke-like symptoms. Some blood tests can also help determine your risk of having a stroke in the future.
The following is a list of blood tests that may be performed as part of your stroke diagnosis or risk evaluation. All of these tests can be done on a simple blood sample, drawn in just a few seconds from a vein in your arm.
CBC & Coagulation
CBC (Complete Blood Count)
This test measures the overall health of your blood, including the quality and number of red blood cells, white blood cells, hemoglobin (the oxygen carrier), platelets, and other factors. A CBC test can diagnose infection, anemia, and other imbalances in the bloodstream; an abnormal platelet count indicates that your stroke may have been caused by excessive bleeding (if your count is too low) or clotting (if it is too high).
Coagulation tests measure how quickly your blood clots. If your blood clots too quickly, your stroke may have been caused by a blood clot. If your blood clots too slowly, your stroke may have been caused by bleeding. This test can also be used to screen for blood clotting problems that are putting you at risk for a stroke in the future. See our article on blood clotting problems for more.
Coagulation tests also help doctors to determine and adjust the doses of blood-thinning drugs used to treat blocked-vessel (ischemic) stroke. See our section on blood thinners and aspirin in the stroke treatment section for more. Coagulation tests produce several different measures of your blood’s clotting ability; common ones include:
- Prothrombin Time (PT)
- Partial Thromboplastin Time (PTT) and Activated Partial Thromboplastin Time (APTT)
- International Normalized Ratio (INR)
Heart Attack Tests
Heart Attack Tests
Patients being evaluated for a blocked-vessel stroke may have blood tests to check for heart muscle damage. A stroke can produce changes on an electrocardiogram (ECG) that are similar to those caused by a heart attack, and some stroke patients also have heart attack symptoms. Tests to find out if heart problems contributed to your stroke may include:
- CK and CKMB
See our article on heart attack blood tests for more information.
Glucose & Electrolytes
A glucose test measures the amount of sugar in your blood. Low blood sugar is a common complication of many diabetes treatments, and can mimic stroke symptoms. High blood sugar levels are a common complication after a stroke. If you have had a stroke, it is important that your blood sugar be monitored and treated with insulin if necessary: very high blood sugar can cause further damage to your blood vessels and brain.
See our article on diabetes for more information on the relationship between blood sugar and stroke.
This test measures the amount of different electrolytes (molecules that carry an electric charge) in the blood, including sodium, potassium, and calcium.
A serum electrolyte test is done in stroke patients because an abnormal electrolyte balance can mimic stroke symptoms. For example, low levels of sodium and potassium can cause confusion, paralysis, and muscle spasms. While you are being treated for stroke, a serum electrolyte test helps your doctor make sure your body has enough water (you are hydrated) and that you maintain a good electrolyte balance, ensuring your body is equipped to recover properly.
A serum electrolyte test can also indicate if you have kidney problems, which may affect the choice of stroke medications, treatments, and diagnostic tests. People with kidney problems may be at risk if they receive a diagnostic test (such as angiography) that uses a dye (called a contrast) to visualize the arteries in the brain; the dye can be toxic to the kidneys in certain patients.
PLAC (Lp-PLA2) Test
The PLAC test measures your blood levels of the enzyme Lp-PLA2, which is related to LDL (bad) cholesterol. Like C-reactive protein, Lp-PLA2 is associated with inflammation and atherosclerosis; high levels of the enzyme are thought to promote the development of vulnerable plaque, buildup on the artery wall that is likely to rupture or break apart, causing a stroke or heart attack.
Many studies have found that Lp-PLA2 predicts your risk of developing heart disease in the future, independent of other heart disease risk factors.1 In the past few years, evidence has been growing that Lp-PLA2 can also help predict your risk of having a first blocked-vessel stroke or your risk of having another stroke if you have already had one.
The largest study so far of blocked-vessel stroke in older women (929 postmenopausal female stroke patients and 935 controls) found that women with high levels of Lp-PLA2 had a 55% higher risk of stroke than women with low levels, even after other risk factors were taken into account. This increased risk was only seen in the 61% of women who were not taking hormone therapy. However, this does not mean you should take hormone therapy to reduce the impact of LP-PLA2; overall, hormone therapy increases your stroke risk. Stroke risk was highest in women who had high levels of both C-reactive protein and Lp-PLA2; these women were twice as likely to have a stroke compared to women with low levels of both markers.
Not all studies have found that Lp-PLA2 can predict stroke more accurately than just looking at standard risk factors, however. In more than 28,000 healthy middle-aged women in the Women’s Health Study, elevated Lp-PLA2 levels did not predict future heart attack or stroke after other risk factors were taken into account.
The PLAC test is approved by the FDA to help assess a person’s risk for coronary artery disease and blocked-vessel stroke. The test may be useful in patients who are at intermediate risk for stroke, in whom it is not clear if medication or other treatment is necessary. For example, in a woman who has low cholesterol and a single major stroke risk factor (such as a family history of stroke), the PLAC test could help doctors better understand her true stroke risk.
For now, the PLAC test is not routinely used to determine your risk of having a stroke. People with higher levels of Lp-PLA2 are at increased risk for stroke, but the cutoff level (above which you can be considered high risk) is not known. In addition, specific treatment to lower Lp-PLA2 levels does not yet exist. Clinical trials are underway on a drug called darapladib to find out if blocking Lp-PLA2 can prevent heart disease and stroke.