Table 2.

Differences between frequencies and titers of positive and negative anti-CCP antibodies among the three groups.

anti-CCP	psoriatic arthritis (n = 41)	rheumatoid arthritis (n = 139)	normal subjects (n = 147)	p*
frequency
positive (n)	5	84	2
negative (n)	36	55	145	< 0.001&
mean titer	positive (U/mL; range)	12.6 (5.5 - 27)	122.4 (5.4 - 200)	5.6 (5.4; 5.8)
negative (U/mL; range)	2.1 (0.1 - 4.9)	2.7 (0.1 - 4.8)	2.4 (0.1 - 4.9)	0.004#
Notes: * calculated with the χ2 test (significant if p ≤ 0,05); & χ2(2, n = 327) = 129.83; p < 0.001; # χ2(2, n = 148) = 11.27; p = 0.004.