A comparison of two fixatives on IFA HEp-2 slides for the detection of antinuclear antibodies

Interkit Reproducibility of the Indirect Immunofluorescence Assay on HEp-2 Cells Depends on the Immunofluorescence Reactivity Intensity and Pattern

Introduction

The indirect immunofluorescence assay on HEp-2 cells (HEp-2/IFA) is used worldwide for screening for autoantibodies to cellular antigens. Cell culture and fixation methods influence the cell distribution of autoantigens and the preservation of epitopes. Therefore, discrepancy of results obtained using different HEp-2/IFA kits (interkit nonreproducibility) is a common phenomenon in the clinical laboratory routine.

Objective

This study evaluated the interkit nonreproducibility of HEp-2/IFA results using samples from patients with systemic autoimmune disease (SAD), nonautoimmune diseases (NAD), and healthy blood donors (HBD).

Methods

Serum from 275 SAD patients, 293 NAD patients, and 300 HBD were processed at 1:80 dilution using four HEp-2 kits according to the manufacturers’ instructions. Interkit reproducibility was determined for positive/negative results and patterns. The agreement of positive/negative results among kits for each sample was determined as the reactivity agreement score (RAS). The pattern reproducibility score (PRS) in each sample was calculated as a function of the number of kits showing equivalent patterns. Qualitative variables and ordinal variables were analyzed by the Chi-square and Mann-Whitney U tests, respectively.

Results

A total of 402 samples were nonreactive in all kits and were considered devoid of autoantibodies. Further analysis included the 466 reactive samples (238 SAD, 119 NAD, 109 HBD). Reactivity to the nucleus had the highest interkit reproducibility (RAS = 83.6), followed by the metaphase plate (RAS = 78.9), cytoplasm (RAS = 77.4), and nucleolus (RAS = 72.4). Interkit reproducibility was higher in SAD (RAS = 78.0) than in NAD (RAS = 70.6) and HBD (RAS = 71.3) groups. Samples with strong reactivity (++++/4 and +++/4) had higher interkit reproducibility than those with weak reactivity (+/4). In the SAD group, RAS for nuclear reactivity was 87.5% for strongly reactive samples as opposed to 4.4% for weakly reactive samples, and the same was observed for NAD and HBD samples. The most robust patterns were the centromere AC-3 (PRS = 78.4), multiple nuclear dots AC-6 (PRS = 73.6), nuclear coarse speckled AC-5 (PRS = 71.3), nuclear homogeneous AC-1 (PRS = 67.9), and the reticular cytoplasmic AC-21 (PRS = 68.6).

Conclusion

Interkit nonreproducibility in HEp-2/IFA is prevalent and occurs with the highest frequency with weakly reactive samples. International initiatives with the engagement of in vitro diagnostic industry are encouraged to promote the harmonization of the properties and performance of HEp-2/IFA commercial kits.

Standardization and Quality Assessment Under the Perspective of Automated Computer-Assisted HEp-2 Immunofluorescence Assay Systems

The recent availability of automated computer-assisted diagnosis (CAD) systems for the reading and interpretation of the anti-nuclear antibody (ANA) test performed with the indirect immunofluorescence (IIF) method on HEp-2 cells, has improved the reproducibility of the results and initiated a process of harmonization of this test. Furthermore, CAD systems provide quantitative expression of fluorescence intensity, allowing the introduction of objective quality control procedures to the monitoring of the entire process. The calibration of the reading systems and the automated image interpretation are essential prerequisites for obtaining reproducible and harmonized IIF test results and form the basis for standardization, regardless of the computer algorithms used in the different systems. The use of automated CAD systems, facilitating control procedures, represents a step forward for the quality certification of the laboratory.

ANA as an entry criterion for the classification of SLE

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease with highly variable clinical and immunological manifestations. In the classification of patients with this condition, the presence of an antinuclear antibody (ANA) is an important element, with new criteria from the American College of Rheumatology and European League against Rheumatism positioning ANA positivity by an immunofluorescence assay on HEp2-cells (HEp2-IFA) or by an equivalent solid phase assay as the entry criterion. This positioning is based on assumptions about the frequency of ANA positivity in SLE as well as the reliability of the assays. Studies indicate that these assumptions are still a matter of uncertainty since both types of assay show considerable variability and patients with SLE may display negative results in ANA testing. These findings suggest caution in positioning ANA positivity as an entry criterion for classification and point to the value of alternative serological approaches for ANA determinations.

The burden of the variability introduced by the HEp-2 assay kit and the CAD system in ANA indirect immunofluorescence test

According to the recent recommendations of the American College of Rheumatology, ANA Task Force, IIF technique should be considered the gold standard in antinuclear antibodies (ANAs) testing. To overcome the lack of standardization, biomedical industries have developed several computer-aided diagnosis (CAD) systems. Two hundred and sixty-one consecutive samples with suspected autoimmune diseases were tested for ANA by means of IIF on routinely HEp-2 assay kit (Euroimmun AG). Assignment of result was made if consensus for positive/negative was reached by at least 2 out of 3 expert physicians. ANA-IIF was also carried out using 3 CAD systems: Zenit G-Sight (n = 84), Helios (n = 85) and NOVA View (n = 92); human evaluation was repeated on the same substrate of each CAD system (Immco, Aesku and Inova HEp-2 cells, respectively). To anonymize the results, we randomly named these three systems as A, B and C. We ran a statistical analysis computing several measures of agreement between the ratings, and we also improved the evaluation by using the Wilcoxon's test for nonparametric data. Agreement between the human readings on routinely HEp-2 assay kit and human readings on CAD HEp-2 assay was substantial for A (k = 0.82) and B (k = 0.72), and almost perfect for C (k = 0.89). Such readings were statistically different only in case A. Comparing experts' readings with the readings of CAD systems, when the samples were prepared using CAD HEp-2 assay kits, we found almost perfect agreement for B and C (k = 0.86; k = 0.82) and substantial agreement for A (k = 0.73). Again, human and CAD readings were statistically different only in A. When we compared the readings of medical experts on routinely HEp-2 assay kit with the output of the CAD systems that worked using their own slides, we found substantial agreement for all the systems (A: k = 0.62; B: k = 0.65; C: k = 0.71). Such readings were not statistically different. The change of the assay kit and/or the introduction of a CAD system affect the laboratory reporting, with an evident impact on the autoimmune laboratory workflow. The CAD systems may represent one of the most important novel elements of harmonization in the autoimmunity field, reducing intra- and inter-laboratory variability in a new vision of the diagnostic autoimmune platform.

Assay variation in the detection of antinuclear antibodies in the sera of patients with established SLE

OBJECTIVE

The expression of antinuclear antibodies (ANA) is considered almost constant in systemic lupus erythematosus (SLE), although recent experience has suggested that many subjects with SLE considered for clinical trials are ANA negative at screening. The objective of this study is to determine whether assay variation can influence ANA detection in patients with established SLE.

METHODS

Sera from 103 patients with established SLE were tested using three different immunofluorescence assays (IFA) for ANA determination. ANA determinations were also performed by an ELISA and bead-based multiplex assay.

RESULTS

With IFA kits, the frequency of ANA negativity varied from 5 to 23 of 103 samples (4.9%-22.3%). The ELISA and multiplex assays showed that 12 (11.7%) and 14 (13.6%) samples were negative, respectively. Samples positive in all assays differed from those with discordant assay results in the frequency of historical anti-double-stranded DNA positivity and low complement levels at the time of blood sampling.

DISCUSSION

These findings indicate that ANA negativity occurs in patients with established SLE although the frequency varies depending on the assay kit. Given the range of negativity with well-validated assays, these findings raise questions about whether ANA positivity should be employed to determine eligibility for clinical trials.

Screening for IgG antinuclear autoantibodies by HEp-2 indirect fluorescent antibody assays and the need for standardization

We evaluated 5 commercially available HEp-2 antinuclear antibody (ANA) indirect fluorescent antibody (IFA) assays using patient serum samples from 45 patients with rheumatoid arthritis, 50 with systemic lupus erythematosus (SLE), 35 with scleroderma, 20 with Sjögren syndrome, 10 with polymyositis, and 100 healthy control subjects. In addition, 12 defined serum samples from the Centers for Disease Control and Prevention and 100 patient serum samples sent to ARUP Laboratories (Salt Lake City, UT) for ANA IFA testing were also examined (n = 372). Standardization among the HEp-2 IFA assays occurred when they exhibited the same titer ± 1 doubling dilution. Agreement of the 5 assays was 78%. Within the specific groups of serum samples, agreement ranged from 44% in scleroderma serum samples to 93% in healthy control subjects, with 72% agreement in the SLE group. Variations in slide and substrate quality were also noted (ie, clarity, consistency of fluorescence, cell size, number and quality of mitotic cells). Along with subjectivity of interpretation, HEp-2 IFA assays are also vulnerable to standardization issues similar to other methods for ANA screening.

Prevalence of antibodies against HEp-2 cell antigen in infants and children hospitalized with respiratory syncytial virus infection

Infants with respiratory syncytial virus (RSV) infection were shown to have antibodies against HEp-2 cell antigen present in RSV-antigen preparation used for immunoblot analysis. The prevalence of anti HEp-2 cell antibodies was examined in infants hospitalized for RSV infection (n = 49, median age 121 days) compared to rotavirus infected children (n = 30, median age 114 days) and to healthy controls (n = 20, median age 150 days). The immunoblot analysis with RSV-infected and non-infected HEp-2 cells as antigen revealed the expected age-dependent low prevalence of G protein antibodies and clear seroconversion of N and P protein antibodies. HEp-2 antibody prevalence was higher in RSV antigen-positive infants (33/49) than in rotavirus antigen-positive (5/30) and RSV antigen-negative infants (4/20), respectively (p < 0.001). Anti HEp-2 antibodies were mostly directed against 47, 46, 33, 30 kD antigens. A multiple regression analysis found the following correlations (odds ratio; 95% confidence interval): 42 kD RSV antibodies (N protein) with pneumonia (7.58; 1.43-40), 94 kD RSV antibodies (G protein) with bronchiolitis (0.064; 0.006-0.686). This study shows repeated well-known features of humoral immunity in RSV infection. The data on anti HEp-2 antibodies point to a role for these pre-existing autoreactive antibodies in the pathogenesis of RSV infection.