Blood Tests: Unraveling Ischemic Stroke Mysteries

A blood test after an ischemic stroke is crucial for recovery and prevention. While there is no blood test to diagnose a stroke, doctors use blood tests to determine the cause of a stroke and the best treatment options. Blood tests can also help predict major stroke risk, show the mechanism of stroke, and predict the outcome of recovery. Doctors will typically start with four primary blood tests, which may rule out other factors that can cause stroke-like symptoms. These include a complete blood count (CBC) test, blood lipid test, markers-of-inflammation tests, and blood chemistry tests.

Complete blood count (CBC)

A complete blood count (CBC) is a blood test that measures the amounts and sizes of red blood cells, white blood cells, platelets, and haemoglobin in a person's blood. It is often part of a routine checkup and can help detect a variety of disorders, including infections, anaemia, diseases of the immune system, and blood cancers.

In the context of an ischemic stroke, a CBC can be used to measure the overall health of a person's blood and help diagnose potential causes of the stroke, such as infection, anaemia, clotting problems, or other blood problems. High red blood cell or platelet levels can cause the kind of clumping that results in clots that trigger an ischemic stroke. On the other hand, very low platelet levels can indicate a person's blood cannot clot, leading to bleeding into the brain and causing a hemorrhagic stroke.

A CBC test can also help rule out other factors that can cause stroke-like symptoms. For example, abnormal inflammatory markers may be present in vasculitis or endocarditis, which can cause similar symptoms to a stroke. Additionally, high glucose levels can cause symptoms similar to a stroke and are an indication of diabetes, an underlying condition that increases the risk of both stroke and heart attack.

The test is performed by taking a blood sample from a vein in the arm using a small needle. The procedure typically takes less than five minutes, and there is usually no special preparation required. However, if other tests are being performed on the same blood sample, the patient may need to fast for several hours beforehand.

Clotting time

Blood clotting tests are used to identify any disorders related to blood hemostasis. Clotting time is the measure of the time taken for a clot to form after bleeding has started. This process is a function of the enzyme thrombin, its precursor prothrombin, and clotting factors. Therefore, clotting time tests help in the diagnosis of various disorders related to clotting factors or deficiencies of vitamin K.

The test tells you how many seconds it took your blood to form a clot. A typical PT result is 10 to 14 seconds. Higher than that means your blood is taking longer than normal to clot and may be a sign of many conditions, including bleeding or clotting disorders, or a lack of clotting factors. A lower number means your blood clots faster than normal, which could be due to taking supplements or eating foods high in vitamin K.

Blood lipid test

A blood lipid test is one of the four primary blood tests doctors will use to determine the cause of a stroke and how to treat it. Blood lipid tests measure good cholesterol levels (high-density lipoprotein, or HDL) and bad cholesterol levels (low-density lipoprotein, or LDL) that may be contributing factors leading to a stroke.

Lipids include fats and cholesterol, both good and bad, that build up in body tissues, including the blood. Cholesterol is a waxy substance in the blood, and having too much of it is a major risk factor for stroke.

A blood lipid test can help doctors determine which interventions may prevent a person from having another stroke in the future.

In a study of 2940 participants, baseline high-density lipoprotein cholesterol, triglyceride, and total cholesterol levels were not associated with the risk of ischemic stroke. However, low-density lipoprotein cholesterol (LDL-C) and non–high-density lipoprotein cholesterol levels were associated with a paradoxical reduction in the risk of stroke.

In another study, patients who had a target LDL cholesterol level of less than 70 mg/dL had a lower risk of subsequent cardiovascular events than those who had a target range of 90-110 mg/dL.

Markers-of-inflammation tests

There are several types of markers-of-inflammation tests, including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) tests. ESR measures how fast red blood cells settle at the bottom of a vertical tube of blood. When there is inflammation, the red blood cells fall faster as higher amounts of proteins in the blood make those cells clump together. CRP is a protein made in the liver that tends to rise when inflammation is present. Normal CRP values are less than 3 mg/L, while values over 3 mg/L are used to identify an increased risk of cardiovascular disease. Other markers-of-inflammation tests include ferritin, fibrinogen, serum amyloid A, cytokines, alpha-1-acid glycoprotein, plasma viscosity, ceruloplasmin, hepcidin, and haptoglobin.

Blood chemistry tests

Additionally, blood chemistry tests can check levels of electrolytes such as sodium and potassium. These tests can also help rule out other factors that may be causing stroke-like symptoms, such as leukemia, anemia, or infection.

In the case of ischemic strokes, which are caused by blood clots in the brain or a blood vessel leading to it, blood chemistry tests can help determine if high cholesterol levels or abnormal glucose levels may have contributed to the stroke.

Overall, blood chemistry tests are an essential tool for doctors to diagnose, treat, and prevent strokes, as well as manage the patient's recovery and prevent future strokes.

Frequently asked questions