Acute phase proteins

The following are direct or indirect measurements of acute phase proteins EXCEPT which one?

a) C-reactive protein

b) Plasma viscosity

c) Haptoglobin

d) Rheumatoid factor

e) Erythrocyte sedimentation rate

Answer: D

Explanation

C-reactive protein (CRP) and haptoglobin are acute phase proteins. These are proteins whose levels fluctuate in response to tissue injury. C-reactive protein is elevated in a wide range of inflammatory diseases such as infections, connective tissue diseases and neoplasias. C-reactive protein was so called, when it was discovered, because it reacted with the C polysaccharide of Streptococcus pneumoniae. Haptoglobin is elevated in haemolysis, but also in many inflammatory processes. Erythrocyte sedimentation rate (ESR) measures how quickly red cells fall through a column of blood and as such is an indirect test of acute phase proteins. ESR has a number of factors, such as

gender and haematocrit  that influence the value generated by the test. It is, however,cheap, quick and easy to perform but is fairly non-specific with regard to the type of inflammatory process detected. Plasma viscosity is also an indirect test of acute phase proteins with results that mirror ESR. It is not, however, affected by haematocrit and is therefore more reliable than ESR. Rheumatoid factor (RhF) is an autoantibody, found in about 75% of people known to have rheumatoid arthritis. It is also elevated in a number of other autoimmune diseases such as Sjögren’s syndrome. The level of RhF may give some indication of severity of the rheumatoid arthritis but is not predictive of an acute inflammatory flare-up.