Serum amyloid A in the assessment of early inflammatory arthritis.
OBJECTIVE
Acute phase serum amyloid A (A-SAA) has been reported to be more sensitive than C-reactive protein (CRP) as a marker of disease activity. It may function in immune regulation and is linked to the development of secondary amyloidosis. We investigated the profile of A-SAA in early inflammatory arthritis and compared A-SAA with CRP and erythrocyte sedimentation rate (ESR) in relation to diagnosis and disease activity.


METHODS
Using a sensitive and specific ELISA, A-SAA was measured in the serum of 140 patients with early arthritis (disease duration 2 weeks to 24 mo, mean 6 mo). CRP was determined using a standard ELISA; ESR and clinical disease activity variables were also recorded.


RESULTS
Sixty-four patients had rheumatoid arthritis (RA), 19 psoriatic arthritis (PsA), 28 undifferentiated arthritis (UA), and 29 other forms of arthritis. A-SAA levels correlated with both CRP (r = 0.73, p = 0.0001) and ESR (r = 0.6, p = 0.0001). The magnitude of the A-SAA response was greater than either the CRP or ESR, and very high A-SAA levels were observed in disease as early as 2 weeks. Highest A-SAA concentrations occurred in RA (median 70.3 mg/l, maximum 1542) compared with the other groups (medians, PsA: 33 mg/l; UA: 12.3 mg/l; other arthritis: 11.2 mg/l), with values > 520 mg/l observed exclusively in RA. A-SAA, unlike CRP or ESR, could distinguish patients with a final diagnosis of RA from those who had persistent UA. In RA, A-SAA provided the strongest correlations with clinical measurements of disease activity. Clinical improvement was also best represented by A-SAA, while disease deterioration was associated with a significant increase in A-SAA values, but not CRP or ESR.


CONCLUSIONS
Compared with ESR or CRP, A-SAA correlates best with markers of disease activity, and in patients with recent onset arthritis, very high levels of SAA occur exclusively in RA. As A-SAA is sensitive to change and accurately reflects alterations in disease status, it is the best marker available for the assessment of inflammatory joint disease.
Cunnane
G
G
Department of Rheumatology, St. Vincent's University Hospital, Dublin, Ireland.
Grehan
S
S
Geoghegan
S
S
McCormack
C
C
Shields
D
D
Whitehead
A S
AS
Bresnihan
B
B
Fitzgerald
O
O
D000293:Adolescent; D000328:Adult; D000368:Aged; D001168:Arthritis / Q000097:blood* / Q000175:diagnosis*; D001799:Blood Sedimentation; D002097:C-Reactive Protein / Q000032:analysis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D000685:Serum Amyloid A Protein / Q000032:analysis*; D012720:Severity of Illness Index; D013997:Time Factors
D000685:Serum Amyloid A Protein; D002097:C-Reactive Protein