Clinical evaluation of various selected ELISA kits for the detection of anti-DNA antibodies

Laboratory evaluation of anti-dsDNA antibodies

Antibodies to dsDNA are an important laboratory parameter for diagnosis, monitoring and classification of systemic lupus erythematosus (SLE). In clinical laboratories, several techniques are used to detect and quantify anti-dsDNA antibodies. Each technique has its advantages and disadvantages regarding sensitivity, specificity, avidity and assay procedure. Assays differ with respect to the antigen source (native versus synthetic versus molecular biological) used and the way the antigen is presented (e.g. in solution, covalently linked to a solid phase,…). Consequently, correlation between assays can be poor and standardization of anti-dsDNA antibody tests is challenging. We here provide an overview of the currently available anti-dsDNA tests frequently used in clinical laboratories [Crithidiae luciliae immunofluorescence test (CLIFT), Enzyme linked immune sorbent assay (ELISA), fluoroenzyme immunoassay (FEIA), chemiluminescence (CIA), multiplexed bead-based assays and Farr-RIA] and their performance characteristics. From this literature study, we concluded that performance characteristics differ between assays. Often, a combination of techniques is necessary for the best result interpretation.

Successful Detection of Renal Involvement in Sjögren's Syndrome Secondary to Systemic Lupus Erythematosus by Renal Biopsy

An 80-year-old man presented with a mildly decreased renal function and increased anti-double-stranded-DNA (anti-dsDNA) antibody levels, and met the diagnostic criteria of the American College of Rheumatology for systemic lupus erythematosus (SLE). However, the incremental increase in creatinine levels and the mild proteinuria were inconsistent with lupus nephritis. We performed a renal biopsy, which revealed interstitial nephritis and minor glomerular abnormalities. Further examinations determined that the renal lesion was due to Sjögren's syndrome secondary to SLE. Following treatment with oral prednisolone, the patient's renal function improved as his anti-dsDNA antibody levels decreased. This case report indicates that renal biopsy should be considered even in elderly individuals when it may assist in the diagnosis, treatment, and prognosis of the patient.

Autoantibody Determination in the Diagnosis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease that usually develops in young women aged 18-50 years and is characterized by the presence of autoantibodies. Diagnosis is difficult as SLE is a great imitator of other diseases. When SLE is suspected clinically in a patient (involvement of two or more organ systems), an initial laboratory evaluation would be antinuclear antibody (ANA) testing. If ANA is negative, SLE is unlikely and results positive at less than 1:40 strongly argue against SLE. Other explanations for organ system involvement should be pursued. Results positive at greater than 1:40 may merit further evaluation for SLE and at times referral to a rheumatologist for a full SLE evaluation. While the American College of Rheumatology classification criteria for SLE are primarily a tool for research, they may be useful clinically, in that those patients fulfilling four or more criteria are highly likely to have SLE.

Detection of anti-dsDNA by ELISA using different sources of antigens

AIM

To compare different sources of DNA for use in ELISA-based assays for anti-dsDNA antibody detection in systemic lupus erythematosus (SLE) diagnosis.

METHOD

Bacterial genomic DNA from Flavobacterium menignosepticum, Proteus vulgalis, Seratia marcescens, Streptococcus pyogenes and Salmonella typhimurium and genomic DNA from human blood were used as antigens for IgG anti-dsDNA detection by enzyme-linked immunosorbent assay (ELISA). Eighty-six sera were tested, 28 derived from patients with SLE, 28 from patients with other rheumatic diseases and 30 from normal human subjects.

RESULTS

Genomic DNA from Flavobacterium menignosepticum and human blood had high sensitivity (75%, 82%) and specificity (91%, 91%) for anti-dsDNA detection in diagnosis of SLE. However, human genomic DNA was the most effective antigen of all antigens studied. The assay had a higher sensitivity but lower specificity than commercial ELISA (61% sensitivity and 95% specificity). There was a high level of correlation between commercial ELISA and ELISA using human genomic DNA as antigen (r=0.776, p<0.001) and they exhibited a high level of diagnostic agreement with each other (kappa=0.890, p<0.001).

CONCLUSION

The genomic DNA from human blood is a potentially useful source of antigen for the detection of anti-dsDNA by ELISA. However, further studies are required to compare the performance of ELISA using this source of antigen against commercial radioimmunoassays for anti-dsDNA detection.

Development of autoantibodies before the clinical onset of systemic lupus erythematosus

BACKGROUND

Although much is known about the natural history of systemic lupus erythematosus (SLE), the development of SLE autoantibodies before the diagnosis of the disease has not been extensively explored. We investigated the onset and progression of autoantibody development before the clinical diagnosis.

METHODS

The Department of Defense Serum Repository contains approximately 30 million specimens prospectively collected from more than 5 million U.S. Armed Forces personnel. We evaluated serum samples obtained from 130 persons before they received a diagnosis of SLE, along with samples from matched controls.

RESULTS

In 115 of the 130 patients with SLE (88 percent), at least one SLE autoantibody tested was present before the diagnosis (up to 9.4 years earlier; mean, 3.3 years). Antinuclear antibodies were present in 78 percent (at a dilution of 1:120 or more), anti-double-stranded DNA antibodies in 55 percent, anti-Ro antibodies in 47 percent, anti-La antibodies in 34 percent, anti-Sm antibodies in 32 percent, anti-nuclear ribonucleoprotein antibodies in 26 percent, and antiphospholipid antibodies in 18 percent. Antinuclear, antiphospholipid antibodies, anti-Ro, and anti-La antibodies were present earlier than anti-Sm and anti-nuclear ribonucleoprotein antibodies (a mean of 3.4 years before the diagnosis vs. 1.2 years, P=0.005). Anti-double-stranded DNA antibodies, with a mean onset 2.2 years before the diagnosis, were found later than antinuclear antibodies (P=0.06) and earlier than anti-nuclear ribonucleoprotein antibodies (P=0.005). For many patients, the earliest available serum sample was positive; therefore, these measures of the average time from the first positive antibody test to the diagnosis are underestimates of the time from the development of antibodies to the diagnosis. Of the 130 initial matched controls, 3.8 percent were positive for one or more autoantibodies.

CONCLUSIONS

Autoantibodies are typically present many years before the diagnosis of SLE. Furthermore, the appearance of autoantibodies in patients with SLE tends to follow a predictable course, with a progressive accumulation of specific autoantibodies before the onset of SLE, while patients are still asymptomatic.

The use and abuse of commercial kits used to detect autoantibodies

The detection of autoantibodies in human sera is an important approach to the diagnosis and management of patients with autoimmune conditions. To meet market demands, manufacturers have developed a wide variety of easy to use and cost-effective diagnostic kits that are designed to detect a variety of human serum autoantibodies. A number of studies over the past two decades have suggested that there are limitations and concerns in the use and clinical application of test results derived from commercial kits. It is important to appreciate that there is a complex chain of users and circumstances that contributes to variations in the apparent reliability of commercial kits. The goal of this review is to identify the principal links in this chain, to identify the factors that weaken the chain and to propose a plan of resolution. It is suggested that a higher level of commitment and partnership between all of the participants is required to achieve the goal of improving the quality of patient care through the use of autoantibody testing and analysis.

The use of laboratory tests in the diagnosis of SLE

ANA IIF is an effective screening assay in patients with clinical features of SLE and will detect most anti-ssDNA, anti-dsDNA, ENAs, and other autoantibodies. False positives are common. The clinical importance cannot be extrapolated from the ANA titre or pattern, although higher titres (> 1/160) are more likely to be important. HEp-2 cells are the most sensitive substrate for ANA detection, but this must be balanced against an increased incidence of insignificant positivity. ANA positive samples should be subjected to more specific assays for the diagnosis of SLE. A combination of ENA (Ro/La/Sm/RNP) and dsDNA assays will detect most patients with SLE as long as the characteristics of the assays used are well understood. ESR and CRP measurements provide useful additional information. Sjogren's syndrome and MCTD will produce overlapping serology with SLE, and anti-dsDNA titres are sometimes seen in autoimmune hepatitis and rheumatoid arthritis. All results should be reported in the light of the clinical details, by an experienced immunologist. A suggested diagnostic protocol is outlined in fig 1. The type of assay used crucially influences the predictive value of the tests. ELISA technology dominates routine laboratory practice, but tends to produce more false positive and true weak positive results, which may reduce the PPV of the test. This can be minimised by using IgG specific conjugates and careful assay validation. The NPV for SLE [figure: see text] is high for most assays but the PPV varies. Where necessary, laboratories should use crithidia or Farr dsDNA assays to confirm dubious ELISA dsDNA results, and ID/IB to confirm dubious ENA results. For monitoring, a precise, quantitative assay is required. It is unclear whether the detection of IgM or low affinity antibodies has a role here. A combination of anti-dsDNA, C3, C4, CRP, and ESR assays provides the most useful clinical information. Anti-ssDNA assays are likely to be useful, and are potentially more robust than anti-dsDNA assays, but require more validation. Local validation of individual assays and EQA participation is essential. Not all assays that apparently measure the same antibody specificities have equal clinical relevance, even within a single technology. Insufficient international or national reference preparations are currently available for many antibody specificities to enable effective standardisation. Quality assurance schemes reveal large differences in units reported by different assays for some analytes, even when calibrated against an IRP or equivalent reference preparation. Serial results can therefore only be compared from the same laboratory at present. Most autoantibodies increase during active disease, but few prospective data are currently available to justify treatment on the basis of rising titres. Further randomised prospective studies are required to examine the importance of antibody isotype and affinity in the monitoring of SLE by individual assay methods. The most important aspect of the appropriate use of laboratory assays is to become familiar with the limitations of the technology currently in use in your local laboratory, and to consult with your clinical immunologist in cases of doubt, preferably before commencing serological screening.