Table 4.

Sensitivity and specificity of aggrecan fragment measurements

Assay	Cut-off	AUC	Sensitivity	Specificity
OA-1 ARGS ELISA	1 pmol ARGS/ml	82%	67%	92%
Alcian blue precipitation	88.5 μg sGAG/ml	63%	40%	92%
1-F21 ELISA	188.5 μg aggrecan/ml	53%	32%	91%
ARGS/sGAG*	5%	83%	65%	96%

*The molar proportion of aggrecan fragments in SF detected as ARGS neoepitope fragments, measured by Alcian blue precipitation and the ARGS ELISA respectively.

Sensitivity = the proportion of positives (diseased) correctly identified by the test.

Specificity = the proportion of negatives (healthy) correctly identified by the test.

AUC = area under receiver operating characteristic (ROC) curve.

Cut-offs were chosen based on ROC curve analysis where the sum of sensitivity and specificity was highest.