Erythrocyte sedimentation rate (ESR) and plasma viscosity (PV) are two laboratory tests used to determine the presence of inflammation in the body. Elevated ESR and abnormality of PV are common findings in various clinical conditions, including infections, autoimmune diseases, and cancer. The two tests have different mechanisms of measurement but share a common principle, which is the aggregation of red blood cells (RBCs) in the presence of inflammatory proteins.
ESR is a simple and inexpensive test that measures the rate at which RBCs settle in a vertical column of blood under gravity. The test is based on the principle that RBCs tend to aggregate and form rouleaux (stacks of coins) in the presence of plasma proteins, such as fibrinogen and immunoglobulins, which are elevated in inflammatory states. The higher the level of these proteins, the faster the RBCs settle, resulting in an elevated ESR. ESR is measured in millimeters per hour (mm/h) and is a non-specific marker of inflammation.
PV, on the other hand, measures the resistance of plasma to flow. It is a more sensitive and specific marker of inflammation than ESR because it reflects changes in the viscosity of the plasma rather than the aggregation of RBCs. PV is measured in centipoise (cP) and is influenced by factors such as hematocrit, fibrinogen, and other plasma proteins. Abnormality of PV indicates an increase in the concentration of plasma proteins, which leads to an increase in viscosity and a decrease in flow.
The combination of elevated ESR and abnormality of PV suggests a more severe inflammatory state than either test alone. The two tests are often used together to monitor the progression and response to treatment of various inflammatory diseases, such as rheumatoid arthritis, lupus, and vasculitis.
In summary, elevated ESR and abnormality of PV are common laboratory findings in various inflammatory conditions. The two tests have different mechanisms of measurement but share a common principle, which is the aggregation of RBCs