CRP is considered a better marker of the acute phase of the inflammatory process and can be used to assess response to therapy. Repeating the test more frequently than every 2-3 days is not indicated. There is also little rationale for performing both CRP and ESR when looking for indirect evidence of systemic or local site infection.
ESR is less sensitive, less specific test than CRP. It may be superior for monitoring disease activity in auto-immune disorders such as rheumatoid arthritis, systemic lupus erythematosis or temporal arteritis.
A useful recent Australian Prescriber guide to these tests is available here.
AIMED - Let's talk about antibiotics 
It’s also important to note that CRP takes up to 12 hours to become abnormal after the onset of an acute systemic infection. Hence a normal value does not exclude sepsis early on in the illness. Conversely, a normal value later on has a good negative predictive value for bacterial sepsis. Procalcitonin appears earlier in the infection process (at 8 hours) and is more specific for systemic infection than CRP. As mentioned, there is scant rationale for doing an ESR as well as a CRP when looking for infection.
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