ANA Screen,IFA, with Reflex to Titer and Pattern/Mixed Connective Panel 2

This panel can be helpful in the diagnosis of individuals with clinical suspicion of mixed connective tissue disease (MCTD). All specimens are tested for antinuclear antibodies (ANAs) with an immunofluorescence assay (IFA) performed on human epithelial type 2 (HEp-2) cells. Specimens with positive ANA IFA results reflex to tests for ANA titer and pattern, RNP antibodies, double-stranded DNA (dsDNA) antibodies, and Scl-70 antibodies to aid in differential diagnosis.

The laboratory evaluation for individuals with clinical suspicion of autoimmune diseases often begins with an ANA screen. The classic ANA IFA on HEp-2 cells is considered by the American College of Rheumatology (ACR) as the current gold standard because of its overall high sensitivity for several autoimmune diseases [1]. Knowing the ANA titer and fluorescent staining pattern can be helpful in interpreting positive results [2]. The first indication of MCTD is often a high ANA titer (>1:1000), which occurs in 94% to 97% of patients with MCTD [3].

Antibodies to RNP, dsDNA, and Scl-70 are included in this panel as reflex tests when the ANA IFA result is positive. The presence of RNP antibodies is considered the serologic hall mark of MCTD and is required to meet diagnostic criteria [3]. The presence of dsDNA and Scl-70 antibodies suggests systemic lupus erythematosus (SLE) and systemic sclerosis, respectively, but does not exclude MCTD [4]. Positive results on certain ANA tests may precede organ involvement (eg, presence of Scl-70 antibodies may precede esophageal involvement) or development of other autoimmune diseases (eg, presence of dsDNA antibodies may precede SLE) [3].

Individuals with negative results on the ANA IFA usually also have negative results on specific autoantibodies. Therefore, subserology testing is not recommended for individuals without positive ANA IFA results and clinical suspicion of relevant autoimmune disease [5]. However, Jo-1 antibody may be detected in ANA IFA-negative patients with some types of myositis, and SSA antibody may be detected in some ANA IFA-negative patients with lupus or Sjogren syndrome [5].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Methodology of testing for antinuclear antibodies (position statement). 2009. American College of Rheumatology. Updated December 2019. Accessed May 15, 2023. https://assets.contentstack.io/v3/assets/bltee37abb6b278ab2c/blta48818378bc89445/acr-position-statement-methodology-testing-antinuclear-antibodies.pdf
2. Tozzoli R, et al. Am J Clin Pathol. 2002;117(2):316-324.
3. Cappelli S, et al. Semin Arthritis Rheum. 2012;41(4):589-598.
4. Kavanaugh A, et al. Arch Pathol Lab Med. 2000;124(1):71-81.
5. Yazdany J, et al. Arthritis Care Res (Hoboken). 2013;65(3):329-339.