Provided are apparatuses and methods for rapid viscometry of whole blood, plasma, and/or whole blood during coagulation. The disclosed technology measures the blood viscosity through the full range of flow rates found in the cardio-vascular system. This in vitro test can be performed on fresh or anticoagulated whole blood to predict the flow properties (e.g., viscosity) anywhere in the body from the aorta to the deep veins of the leg. The result is a flow-rate dependent blood viscosity curve (viscosity profile) that helps the clinician predict and manage the patient's vulnerability to thrombosis and embolism, which is of particular relevance to COVID-19 patients and/or ICU patients.