Erythrocyte Sedimentation Rate (ESR)

Question 1

Define Erythrocyte Sedimentation Rate (ESR)?

Answer 1

The rate at which red blood cells sediment in 1hr

Question 2

List some indications for ESR testing?

Answer 2

Indications:
• Screening for disease presence and severity- infection and inflammatory diseases
• Diagnosis and monitoring of polymyalgia rhematica and temporal arteritis
• Monitoring progression of RA, lymphomas, MM, macroglobulinaemia (lymphoplasmacytic lymphoma, NHL)

Question 3

Describe the method of ESR analysis?

Answer 3

Analysis:
⇒ Venepuncture -> 4mL blood colleted in EDTA tube (chelates calcium to prevent clotting)
⇒ Filled to line (ensuring correct ratio of blood to anticoagulant)
⇒ Blood mixed well
⇒ Placed in Wintrobe sedimentation tube (100mm long)
- Note: Westergren-Katz tube 300mm long (allowing larger max value) but requires sodium citrate
⇒ Left for 1hr on specialised rack with graduations
⇒ Height of clear plasma above upper margin of sedimenting RBCs read to nearest mm -> gives ESR in mm/hr

Question 4

Describe the pathophysiology of ESR?

Answer 4

ESR: rate at which erythrocytes suspended in plasma settle in a vertical tube -> indirect measurement of inflammation
• Normally: erythrocyte negative change (zeta potential) prevents sedimentation

• Inflammatory state:
⇒ Macrophages release IL-6
⇒ Promotes hepatic synthesis of fibrinogen (positive charge)
⇒ Causes RBC to stick together in stacks (Rouleaux formation)
⇒ Allows clumping and sedimentation
• Antibodies can also cause this RBC stacking and sedimentation

Question 5

How may ESR results be interpreted? What can cause elevation or reduction?

Answer 5

Normal ranges:
o Males <15 mm/hr
o Females <20mm/hr

Elevation causes:
o Infection
o Inflammation
o Malignancy (e.g. MM w paraproteinaemia) 
o Pregnancy
o Anaemia

Reduction causes:
o Polycythemia (abnormally increased RBC production in BM)
o Abnormal RBCs (Sickle cell, hereditary spherocytosis, CCF)

Question 6

List some possible sources of error in ESR analysis?

Answer 6

Sources of error:
• False elevation- due to sedimentation tube tilted, high temps
• False reduction- due to shorter sedimentation tube, low temp, delayed testing post-venepuncture
• Incorrect proportion of anticoagulant
• Haemolysed sample
• Failure to read at 1hr