Line blot immunoassays in idiopathic inflammatory myopathies: retrospective review of diagnostic accuracy and factors predicting true positive results

Table 3 Associations between true positive myositis-specific and myositis-associated autoantibodies and clinical factors

Factor	Any true positive MSA/MAA	Any false positive MSA/MAA	OR	P	CI
Female gender	78% (80/103)	67% (50/75)	1.74	0.10	0.89–3.39
Mean age of onset (SD)	50 (13)	52 (15)	0.99	0.35	0.96–1.01
Pre-test working diagnosis of IIM	59% (61/103)	19% (14/75)	50.8	<0.001	13.66–189.22
Biopsy in keeping with inflammatory myopathy	50% (7/14)	28% (7/25)	2.57	0.18	0.66–10.06
Myopathic EMG changes	64% (21/33)	43% (12/28)	2.33	0.11	0.83–6.54
Highest recorded CK (mean, SD)	1377 (3502)	563 (910)	1.0	0.108	1.00–1.00
Strong positive antibody result	70% (72/103)	35% 26/75	4.38	<0.001	2.32–8.26

MSA myositis-specific autoantibody, MAA myositis-associated autoantibody, OR odds ratio, P p-value, CI confidence intervals, SD standard deviation, IIM idiopathic inflammatory myopathy, EMG electromyography, CK creatine kinase

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