Urine β-2-glycoprotein 1 as a biomarker for diagnosis of systemic lupus erythematosus

Objective The need for a biomarker with robust sensitivity and specificity in diagnosing systemic lupus erythematosus (SLE) remains unmet. Compared with blood samples, urine samples are more easily collected; thus, we aimed to identify such a biomarker based on urinary proteomics which could distinguish patients with SLE from healthy controls (HCs). Methods Urine samples were collected from 76 SLE patients who visited rheumatology clinic in 2019 at Asan medical center and from 25 HCs. Urine proteins were analyzed using sequential windowed acquisition of all theoretical fragment ion spectra-mass spectrometry, and the candidate marker was confirmed by enzyme-linked immunosorbent assay (ELISA). Receiver operating characteristic curve analysis was used to determine the diagnostic value of the candidate biomarker. Results Of 1157 proteins quantified, 153 were differentially expressed in urine samples from HCs. Among them were previously known markers including alpha-1-acid glycoprotein 1, alpha-2-HS-glycoprotein, ceruloplasmin, and prostaglandin-H2 D-isomerase. Moreover, the amount of beta-2 glycoprotein (APOH) was increased in the urine of patients with SLE. The ELISA results also showed the level of urine APOH was higher in patients with SLE than in HCs and patients with rheumatoid arthritis. Moreover, the level was not different between SLE patients with and without nephritis. The urine APOH had an area under the curve value of 0.946 at a cut-off value of 228.53 ng/mg (sensitivity 91.5%, specificity 92.0%) for the diagnosis of SLE. Conclusion The results indicate that the urine APOH level can be an appropriate screening tool in a clinical setting when SLE is suspected.

Automated summary

This study identified urinary APOH as a potential biomarker for diagnosing SLE, with high sensitivity and specificity, making it a promising screening tool in clinical settings when SLE is suspected.