erythrocyte sedimentation rate
Summary
Erythrocyte sedimentation rate (ESR) is a nonspecific marker of inflammation measuring how quickly RBCs settle in a vertical tube over one hour. Elevated fibrinogen and other acute-phase proteins cause RBCs to aggregate (rouleaux formation), increasing sedimentation rate. It's commonly used to monitor conditions like temporal arteritis, polymyalgia rheumatica, and rheumatoid arthritis.
Detail
ESR reflects the degree of inflammation in the body by measuring the rate at which red blood cells settle in anticoagulated blood over one hour. During inflammation, the liver increases production of acute-phase reactants, particularly fibrinogen, which coats RBCs and reduces their negative surface charge (zeta potential), promoting rouleaux formation (stacking of RBCs like coins). This increased aggregation causes cells to settle faster, raising ESR.
Clinical uses: ESR is classically markedly elevated (often >100 mm/hr) in temporal (giant cell) arteritis and polymyalgia rheumatica, making it a key diagnostic and monitoring tool. It is also elevated in other inflammatory/autoimmune conditions (rheumatoid arthritis, SLE), infections, malignancies (especially multiple myeloma due to paraproteinemia), and pregnancy.
Limitations: ESR is nonspecific—many conditions can elevate or lower it. Causes of falsely low ESR include polycythemia, sickle cell disease (abnormal RBC shape prevents rouleaux), microcytosis, hypofibrinogenemia, and CHF. Causes of elevated ESR besides inflammation include anemia, female sex, advanced age, and macrocytosis.
ESR is often compared with CRP (C-reactive protein): CRP rises and falls more quickly, making it better for monitoring acute changes, while ESR remains a historical standard for chronic inflammatory conditions like GCA/PMR. Multiple myeloma is a classic board question due to extremely high ESR from paraprotein-induced rouleaux formation despite the absence of typical inflammatory cytokines driving fibrinogen synthesis.
Board relevance: Know classic associations (GCA, PMR, multiple myeloma), the mechanism of rouleaux formation, and the difference between ESR and CRP kinetics and specificity.
Sources
- First Aid for the USMLE Step 1
- Robbins Basic Pathology
- UpToDate: Acute phase reactants
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.