Are there any blood tests to show the forming or potential of a stroke?

No: But if your cholesterol, diabetes, or blood pressure is not controlled, your risk increases significantly. Also, if you have heart valve disease, an arrhythmia like atrial fibrillation, cancer, or clotting disorder, that increases the risk & you should be on appropriate therapy (such as warfarin at the right INR range). The best prevention is taking all meds prescribed & close, frequent monitoring.

None specific: There are no lab tests specific for impending stroke. The risk factors for atherosclerosis and vascular disease could serve as markers of risk of stroke as these do for cardiac disease. Elevated cholesterol and ldl, low hdl, increases triglycrides are usual risk factors. Other risk factors that are not lab tests are hypertension, smoking, excessive alcohol intake.