Table 2.

Subgroup analysis of serum COMP with different unit of measure and disease severity

Subgroups	Number of study	Mean difference	95% CI	P
Unit of measure
U/L	3	2.13	0.11, 4.16	0.04
μg/ml	6	1.00	0.37, 1.63	0.002
Disease severity
K-L 1 VS K-L 2	3	0.79	0.34, 1.25	0.0007
K-L 1 VS K-L 3	3	1.08	0.44, 2.60	0.16
K-L 1 VS K-L 4	3	1.61	0.57, 2.65	0.002
K-L 2 VS K-L 3	6	0.44	0.04, 0.85	0.03
K-L 2 VS K-L 4	7	0.61	0.17, 1.05	0.007
K-L 3 VS K-L 4	5	0.41	0.15, 0.68	0.002

K-L Kellgren-Lawrence classification, CI confidence intervals