Factors that decrease the Erythrocyte Sedimentation Rate

Dear Ask The Doctor: I got a copy of my blood test in the mail today and the Sedimentation Rate Westergren 1mm/hr. What does this rate mean as it seems very low to me.

Dear Tammy: Erythrocyte sedimentation rate or ESR is a screening test that indirectly measures the presence of inflammation in the body. When anticoagulated whole blood is allowed to stand in a narrow vertical tube for a period of time, the red blood cells, under the influence of gravity, settle out from the plasma. The rate at which they settle is measured as the number of millimeters of clear plasma present at the top of the column after one hour (mm/hr). The Westergren method requires collecting 2 ml of venous blood into a tube containing 0 .5 ml of sodium citrate.

Normal ESR in mm/hr can be roughly calculated from the formula: [Age in years + 10 (if female)]/2, therefore your normal would be <30mm/hr, if you are approximately 50 years old. Chronic inflammatory diseases increase ESR including Rheumatoid Arthritis, vasculitis and collagen disorders. A decreased ESR reading may be due to abnormally shaped RBC (sickle cells, spherocytosis), polycythaemia or technical factors including: short ESR tubes, low room temperature, delay in test performance (>2 hours), clotted blood sample, excess anticoagulant, bubbles in tube.