Introduction Double-stranded-DNA antibodies (antiDNAds) are the most frequently detected serological markers in patients with Systemic Lupus Erythematosus (SLE). In clinical practice, it is usually determined by the ELISA technique with a specificity of 91–96%. There is another technique with a specificity of 98–100%, which is performed by immunofluorescence (IF) using Crithidia lucilae (CL) parasite.

Purpose To determine anti-DNA by CL in patients with ANA and positive anti-DNAds by ELISA.

To analyse whether there is a relationship between the patients who meet the 2019-ACR-EULAR classification criteria for SLE, and the positivity of anti-DNA by CL.

Methods Bicentric retrospective observational study (Hospital Universitari Germans Trias i Pujol and Hospital General de Granollers).

Patients with ANA ≥1/320 and DNA by ELISA >100IU/mL between 2018–2019 were collected. All underwent the IF CL test. The classification criteria for SLE ACR-EULAR 2019 were applied.

Conclusions Anti-DNA CL test could be useful to discriminate patients with anti-DNA positive test by ELISA and low suspicion of SLE. In our series 95.7% of the patients with CL negative test did not meet SLE criteria.

SLE in elderly behaves different than in younger patients. In our population:

⋄ Age over 65 years: anti-DNA CL test does not allow discrimination between those who meet the SLE criteria and those who don’t.

⋄ Age under 65 years: anti-DNA CL test presents a high correlation with the clinical and analytical data of the patients.

This test could be very useful in clinical practice to complement diagnostic criteria in SLE patients <65 years of age.