Section 864.7525 - Heparin assay(a)Identification. A heparin assay is a device used to determine the level of the anticoagulant heparin in the patient's circulation. These assays are quantitative clotting time procedures using the effect of heparin on activated coagulation factor X (Stuart factor) or procedures based on the neutralization of heparin by protamine sulfate (a protein that neutralizes heparin).(b)Classification. Class II (performance standards).45 FR 60623, Sept. 12, 1980