Paper I
Question
Factors affecting Erythrocyte Sedimentation rate
Answer
ESR measures the rate at which red cells settle in anticoagulated blood over one hour, and is influenced by factors affecting red cell aggregation (rouleaux formation).
Factors that increase ESR
- Increased plasma fibrinogen and immunoglobulins (acute phase response — infections, inflammation, malignancy, autoimmune disease)
- Anaemia (reduced red cell mass alters the ratio of plasma to cells, favouring rouleaux)
- Pregnancy
- Multiple myeloma (markedly elevated due to high monoclonal immunoglobulin)
- Increasing age
Factors that decrease ESR
- Polycythaemia (increased red cell mass resists settling)
- Sickle cell disease (abnormal cell shape impairs rouleaux formation)
- Spherocytosis
- Extreme leucocytosis
- Hypofibrinogenaemia
- Congestive cardiac failure
Technical factors
- Temperature, tube tilt/vibration, and time delay before testing can also affect results