ESR more sensitive than CRP to changes in RA disease activity www.jointandbone.org

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May 17, 2004

ESR more sensitive than CRP to changes in RA disease activity

Bethesda, MD - One of clinical medicine's oldest toolsthe erythrocyte

sedimentation rate (ESR)surpassed serum C-reactive protein (CRP) as a

measure of rheumatoid arthritis (RA) activity and may be better for

monitoring response to disease-modifying antirheumatic drug (DMARD)

treatment, according to a meta-analysis by Dr M Ward (National

Institute of Arthritis and Musculoskeletal and Skin Diseases, NIH, Bethesda,

MD) [1].

" The ESR is cheaper and faster and appears to be more sensitive to change.

The results are a bit surprising, because the tendency in recent years has

been to favor CRP. "

" This study examined only sensitivity to change and not validity or

reliability. These other considerations may influence the choice of test.

However, holding these factors constant and knowing what we do about the

reliability and validity of these tests, the ESR is cheaper and faster and

appears to be more sensitive to change. The results are a bit surprising

because the tendency in recent years has been to favor CRP, " Ward tells

rheumawire.

In an accompanying editorial, Drs Harold us and Ernest Brahn (University

of California, Los Angeles School of Medicine) write, " In view of

substantial evidence that treatments that control CRP and ESR reduce

radiographic joint damage, it is worthwhile for clinicians to follow the ESR

or CRP when treating individual RA patients. If they can do ESR in their

office or a reliable local laboratory that can report the results within 1

or 2 hours, ESR may have advantages for monitoring individual responses to

DMARD therapy " [2].

Analysis included studies with ESR, CRP data from same patients

The chief objective of Ward's study was to compare the relative sensitivity

to change of the ESR and CRP in RA. " One reason for the lack of strong

preference for either test may be that few comparisons of their evaluative

properties have been done, " he points out.

To help fill that gap, Ward searched Medline for clinical trials and

observational studies that measured both ESR and CRP in the same patients at

the start of treatment with either a DMARD or corticosteroids and again

after 4 to 24 weeks of treatment. He also searched the Cochrane Database and

reference lists of retrieved articles for additional studies. Trials of

intravenous corticosteroids were excluded. He harvested 123 studies from

this field of data and winnowed that to 60 studies with 90 active treatment

arms by casting out studies that reported only median values or that did not

report follow-up data, baseline means or standard deviations, or

quantitative measures of CRP.

The most common drugs used in the treatment arms of the 63 studies were

methotrexate, cyclosporine, sulfasalazine, and combination therapies. Of the

studies, 62% were clinical trials and 38% were observational studies.

" In the 36 treatment arms that reported results at 12 weeks, the ESR was

more sensitive to change than the CRP, with a paired difference in effect

sizes of 0.09 units (95% CI 0.03-0.15; p=0.005). In the 76 treatment arms

that reported results at 24 weeks, the ESR was also more sensitive to change

than the CRP, with a paired difference in effect sizes of 0.11 units (95% CI

0.05-0.17; p=0.0004), " Ward reports. He estimates that the ESR is 15% to 20%

more sensitive to change than CRP.

Ward points out that ESR may be considered a less specific measure of the

acute-phase response than CRP because it is influenced by many factors other

than systemic inflammation, including age, sex, red-blood-cell morphology,

hemoglobin concentration, and serum levels of immunoglobulins and rheumatoid

factor. " However, " he notes, " if the ESR also captures changes in

hemoglobin, immunoglobulin, and rheumatoid factor concentrations with

treatment, the association of the ESR with these other markers of

inflammation may enhance its sensitivity to change. "

Study finds " real differences in sensitivity to change "

" These interesting findings are derived from a large number of clinical

trials and appear to reflect real differences in the sensitivity to change

of the 2 measures, " write us and Brahn. But they warn that since ESR

decreases with increases in the time and storage temperatures between

drawing the specimen and performing the test and can also change if the tube

is not held vertical or is subject to vibration, the test should be done in

the office or at a nearby laboratory where technicians are conscious of the

fact that time is of the essence and don't set the tube down on a lab bench

with a centrifuge rumbling nearby.

us and Brahn also point out that Ward's study " does not claim to address

the more critical questions of which surrogate marker correlates best with

actual improvement in clinical, functional, or structural outcome with a

given therapy " but only measures the change over time compared with baseline

after initiation of therapy.

Janis

Sources

1. Ward MM. Relative sensitivity to change of the erythrocyte sedimentation

rate and serum C-reactive protein concentration in rheumatoid arthritis. J

Rheumatol 2004 May; 31(5):884-95.

2. us HE, Brahn E. Is erythrocyte sedimentation rate the preferable

measure of the acute phase response in rheumatoid arthritis? J Rheumatol

2004 May; 31(5):838-40.