The primary objective of the study is to determine the prevalence of aspirin resistance in chronic kidney disease patients. The secondary objectives are to determine possible risk factors contributing to aspirin resistance in this population.

A cross-sectional of "aspirin resistance in hemodialysis patients" previously done in our institution showed that 23/66 (34.7%) hemodialysis patients were aspirin resistant. In a recent systematic review, renal impairment was associated with aspirin resistance . This association was seen in only two out of the twenty studies used in this meta-analysis . Both these studies are from the same center with a predominant Asian population. In this study we will try to evaluate the prevalence of aspirin resistance in CKD patient without being limited to a specific ethnicity.

Inclusion Criteria:

• Patients with known structural kidney disease as evident by history or by urinalysis and CKD stage III or IV determined by MDRD formula and who are taking aspirin.

Exclusion Criteria:

• Younger than 18 years of age.
• Bleeding disorder or myeloproliferative disorders.
• Thrombocytopenia with platelets < 100.000.
• Malignancy.
• Acute hemorrhagic disease.
• A recent history of receipt of platelet glycoprotein IIb/IIIa blockers.
• Liver disease as evident by abnormal liver function and total bilirubin > 2mg/dl.
• use of anticoagulation.

Patients presenting to the nephrology clinic at SIUH and the nephrology clinic at Staten Island rehab and the admitted patients who give consent.