Introduction: Leptin regulates the organism’s immune response. Juvenile idiopathic arthritis (JIA) is a chronic joint disease in children, leading to chronic changes in motor organs.

Material and methods: In children with JIA (n = 42) and healthy subjects (n = 28), leptin concentration (LEP), body mass index (BMI), haematocrit (HTC), haemoglobin (HB), morphotic elements (WBC,LYMPH), erythrocyte sedimentation rate (ESR), and ANA Hep-2 antibodies were analysed. JIA group was divided into: children with a longer (51–148 months) (IA) n = 22 and a shorter disease period (2–18 months) (IB) n = 20.

Results: Only 58.3% of the IA and 50% of the IB group had ANA Hep-2 confirmed. The ill children had higher and more diversified LYMPH and ESR levels compared to the healthy children. The highest LEP for the IA group was 37.5 ng/cm3, (Me 5.85), for IB — 40.10 ng/cm3, (Me 2.46) as compared to the IC — 3.74 ng/cm3 (Me 2.85), respectively. The average BMI value for the IA group was 16.61 kg/m2, for IC it was 18.91 kg/m2, and the median for IB was 15.89 kg/m2. Children with BMI values < 23 kg/m2 from the IA and IB group had a reduction in LEP as compared to control group (p = 0.04). The relationship between the illness and LEP diversification per BMI unit was found in both groups. Children with a shorter illness period had higher LEP differentiation per BMI unit compared to the healthy children.

Conclusions:

1. Children with juvenile idiopathic arthritis with BMI < 23 kg/m2 had lower leptin concentrations than healthy subjects.
2. Ill children with a shorter-term disease had a higher diversification of leptin concentration per BMI unit as compared to healthy controls. (Endokrynol Pol 2015; 66 (5): 417–421)