Objectives:
Osteoarthritis (OA) is the most widespread joint disease and is a major cause of joint pain and disability in the middle aged and elderly population. The diagnosis of OA is based on clinical and radiographic changes that occur late after disease progression, and hence does not allow early detection of structural damage. Therefore, there is an acute need for reliable biochemical markers that can facilitate its earlier diagnosis. This study was commenced to identify fibulin-3 levels in serum and urine of patients with primary knee OA and to investigate their relationship with severity of the disease.

Material and methods:
Fifty female patients with primary knee OA were compared to 25 healthy female controls. Fibulin-3 in serum and urine were measured using enzyme-linked immunosorbent assay (ELISA). Severity of knee pain was assessed by the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index and the Knee Outcome Survey Activities of Daily Living (KOS-ADL) scale. Radiographic grading of knee OA was performed by Kellgren-Lawrence (K-L) criteria.

Results:
Serum and urine fibulin-3 were higher in patients (286.00 ±145.00 ng/ml and 104.60 ±32.73 ng/ml, respectively) than in controls (26.00 ±5.77 ng/ml and 13.60 ±4.21 ng/ml, respectively). Fibulin-3 in serum and urine correlated (p < 0.001) with each other (r = 0.930) and with the severity of knee pain by WOMAC index (r = 0.909 and 0.928, respectively), inversely correlated with KOS-ADL (r = –0.913 and –0.953, respectively), and with radiographic grading of K-L (r = 0.855 and 0.875, respectively).

Conclusions:
Fibulin-3 serves as a biomarker of knee OA disease severity and could predict disease progression. Assessing urine fibulin-3 could be an applicable and easy method to diagnose knee OA and to follow up disease progression.