ESR and APR

 Q: 'Erythrocyte sedimentation rate' (ESR) is a/an ____________ acute phase reactant? (select one)

A) direct

B) indirect

Answer: B

Acute phase reactants (APR) are the proteins whose serum concentrations increase (positive) or decrease (negative) by at least 25 percent during inflammatory states such as infection, trauma, tumor, infarction, or autoimmune diseases. 

'Erythrocyte sedimentation rate' (ESR) is actually not a protein, rather it represents the increased viscosity of the serum due to these acute-phase proteins, mostly fibrinogen. That's why it is called indirect APR.

#inflammation

Reference:

Bedell SE, Bush BT. Erythrocyte sedimentation rate. From folklore to facts. Am J Med 1985; 78:1001.