PURPOSE. SLE is difficult to diagnose due to the lack of reliable diagnostic tests and variability in clinical presentation. The current “gold standard” diagnostic laboratory assays include antinuclear antibodies (ANA), which have high sensitivity, but poor specificity for SLE, and antibodies to ds-DNA, which are specific to SLE, but are present in only half of the patients. A new laboratory assay measuring products of complement activation bound to RBCs (c-RBC) may enhance earlier diagnosis of SLE due to a favorable combined sensitivity and specificity for SLE. We evaluated the incremental costs and effectiveness associated with this test, and identified the most efficient method of its use for SLE diagnosis in comparison to the traditional diagnostic tests.

METHODS. The target population was women at high risk for SLE. A Markov model was developed to evaluate the c-RBC test over a 10-year period in terms of cost per quality-adjusted life-years (QALY) gained. The model assessed patients tested with one of three clinically plausible c-RBC strategies over patients tested traditionally with ANA and ds-DNA tests. We assumed that a prophylactic dose of prednisone given to patients would prevent disease progression if correctly diagnosed, but might also induce toxic side effects (base case disutility 0.84) if applied inappropriately. Sensitivity analyses were conducted to examine the impact of the testing strategies over a range of disutility values associated with treatment side effects. Model parameters were estimated using published and unpublished data sources.

RESULTS. Testing strategy 1, where ANA+ was followed by c-RBC and RBC+ was followed by ds-DNA, added 0.0043 QALY per person and saved $19.3 per person. Two other c-RBC strategies were assessed: (2) ANA+ followed by c-RBC, and c-RBC- followed by ds-DNA; (3) ANA (any result) followed by c-RBC, and ANA+, c-RBC- followed by ds-DNA. These two strategies were dominated by the traditional testing strategy (ANA+ followed by ds-DNA) under the base case model parameters. However, if impact of side effects of prophylactic treatment was set as negligible (utility equal to the value of non-SLE target population), the RBC test yields $26,439 and $55,254 per QALY for these two strategies.

CONCLUSION. Using the RBC biomarker along with the traditional tests can be cost effective for the diagnosis of SLE. Testing strategy 1 appeared to be the most efficient.