Session Information
Session Type: Abstract Submissions (ACR)
Background/Purpose: Anti-nuclear antibody (ANA) is considered a screening method for diagnosis of autoimmune disorders. Immunoflorescence ANA assay (IF) remains the gold standard for detection of ANA as per the 2011 ACR position statement. Many laboratories perform immunoassays for detection of ANA as it is less labor-intensive to perform.
Methods: We collected data prospectively on patients tested for ANA by multiplex immunobead assay MIA (BioPlex ANA screen, Bio-Rad Laboratories, Hercules, CA, USA) and IF assay (HEp-2000 (Immuno Concepts, Sacramento, CA, USA) from chart review of rheumatology patients from March 2011 to May 2012. Patients were separated into 4 groups based on positive and negative ANA by MIA and IF assay. Data were collected by individual chart review including age, gender, ethnicity, and indication for ANA testing. Sensitivity and specificity of the immuno assay were determined using the IF results as the “gold standard”.
Results: One hundred and ten (110) patient samples were tested for both assays. Multiplex immunobead assay (MIA) were considered positive based on the manufacturer’s instructions, and IF was considered positive at a titer ≥ 1:160; 12 (10%) were positive by both assays and were considered true positives (TP), 74 (67%) were negative by both or true negatives (TN); 15 (14%) were positive by IF and negative by MIA and were false negatives (FN); 9 (8%) were positive by MIA and negative by IF, or false positives (FP). (Table 1) Indications for ANA testing in the false negative group included systemic sclerosis, polymyositis, rheumatoid arthritis on treatment with anti-TNF therapy, undifferentiated connective tissue disorders, and polyarthralgias (Table 2). Sensitivity and specificity for the multiplex immunoassay was 44%, and 89%, respectively.
Conclusion: Our study reveals a low sensitivity with high rate of false negatives when MIA is used for ANA screening compared to IF in a real world rheumatology setting of patients presenting with a variety of autoimmune diseases. Patients misclassified by the MIA included patients with definite ANA-associated autoimmune diseases. These data suggest that screening with an immuno assay would result in misclassification and potential delay or missed diagnoses of certain systemic autoimmune diseases. Immunoflorescence assay should remain the preferred assay for ANA testing in patients with suspicion of autoimmune disorders until until high sensitivity platforms are developed.
Table 1. Comparison of ANA MIA and IF
|
|
IF positive (≥1:160) |
IF negative |
|
Multiplex positive n (%) |
12 (10%) TP |
9 (8%) FP |
|
Multiplex negative n (%) |
15 (14%) FN |
74 (67%) TN |
Sample size 110
Table 2. Baseline Demographic comparison
|
|
Multiplex +, IF+ (TP) |
Multiplex-, IF- (TN) |
Multiplex+, IF- (FP) |
Multiplex-, IF+ (FN) |
|
Age (mean±SD)yrs |
45±13 |
48±15 |
47±18 |
48±16 |
|
Females n (%) |
11 (91%) |
59 (79%) |
8 (89%) |
13 (86%) |
|
Ethnicity*(%) |
AA (16%) C (25%) H (50%) |
AA (13%) C (70%) H (9%) |
AA (33%) C (44%) H (11%) |
AA (46%) C (46%) |
|
Indication for testing/Clinical diagnosis (n) |
|
|
|
|
|
SLE |
5 |
1 |
1 |
– |
|
Sjogren’s |
1 |
– |
– |
– |
|
RA |
1 |
9 |
1 |
2 |
|
Systemic sclerosis/PM/DM |
– |
– |
– |
2 |
|
Polyarthralgias |
2 |
30 |
2 |
6 |
|
UCTD |
2 |
– |
– |
3 |
|
Others |
2 |
32 |
5 |
1 |
*AA African American, C Caucasian, H Hispanic
Disclosure:
N. Dang,
None;
B. E. Harper,
None;
E. B. Gonzalez,
None;
S. S. Pierangeli,
BioRad Laboratories,
8;
T. M. Parekh,
None;
M. J. Loeffelholz,
BioRad Laboratories,
2;
K. K. Bufton,
None.
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