Disease Activity Scores using C-reactive protein.

C-reactive protein (CRP) may be used as an alternative to ESR in the calculation of the DAS or DAS28, using the formulas below. CRP is a more direct measure of inflammation than ESR, and it is more sensitive to short-term changes [Kushner 1991]. CRP production is associated with radiological progression in RA [Van Leeuwen 1993], and is considered at least as valid as ESR to measure RA disease activity [Mallya 1982, Wolfe 1997]. Another advantage of determination of CRP is that waiting time for the laboratory result is shorter and that in case of multicenter studies a central laboratory can be used.

For obtaining sensible results in the case of low disease activity, it is advised to make general use of a CRP test with a lower detection level of 1.0 mg/l. The CRP test should have been calibrated by the laboratory using a standardised method, either CRM 470 of the International Federation of Clinical Chemistry, or the WHO reference standard for CRP immunoassay 85/506.

The following formulas to calculate the DAS or DAS28 using CRP (mg/L) give good estimations of the original DAS or DAS28 values on a group level. It is strongly advised to adhere either to ESR or to CRP determinations.

DAS-4(crp) = 0.54*sqrt(RAI)+ 0.065*SJC44 + 0.17*ln(CRP+1) + 0.0072*GH + 0.45
DAS-3(crp) = 0.54*sqrt(RAI)+ 0.065*SJC44 + 0.17*ln(CRP+1) + 0.65

RAI: Ritchie Articular Index; SJC44: 44 Swollen joint count; CRP: C-reactive protein; GH: General Health on a 100mm. Visual Analogue Scale.


DAS28-4(crp) = 0.56*sqrt(TJC28) + 0.28*sqrt(SJC28) + 0.36*ln(CRP+1) + 0.014*GH + 0.96
DAS28-3(crp) = [0.56*sqrt(TJC28) + 0.28*sqrt(SJC28) + 0.36*ln(CRP+1)] * 1.10 + 1.15

TJC28: 28 Tender joint count; SJC28: 28 Swollen joint count; CRP: C-reactive protein; GH: General Health on a 100mm. Visual Analogue Scale.

A web calculator for these complicated formulas will be available soon.


Kushner I. C-reactive protein in rheumatology. Arthritis Rheum 1991;34(8):1065-68.

Van Leeuwen MA, Van Rijswijk MH, Van der Heijde DMFM, Te Meerman GJ, Van Riel PLCM, Houtman PM, Van de Putte LBA, Limburg PC. The acute phase response in relation to radiographic progression in early rheumatoid arthritis: a prospective study during the first three years of the disease. Br J Rheumatol 1993;32(suppl 3):9-13.

Mallya RK, De Beer FC, Berry H, Hamilton EDB, Mace BEW, Pepys MB. Correlation of clinical parameters of disease activity in rheumatoid arthritis with serum concentration of C-reactive protein and erythrocyte sedimentation rate. J Rheumatol 1982;9(2):224-8.

Wolfe F. Comparative usefulness of C-reactive protein and erythrocyte sedimentation rate in patients with rheumatoid arthritis. J Rheumatol 1997;24:1477-85.