Table 1. Urine samples classified according to U _Osm, U _SG and U _Col values; followed by metrics from ROC analysis.

Criterion value for test measure (USG, UCol)	Reference measure (UOsm)		Metrics from ROC analysisa
	UOsm >500 (n=295)	UOsm ⩽500 (n=521, UCol) (n=522, USG)	Sensitivity	Specificity	Accuracy	PPV	NPV
USG ⩾1.013 (n=307)	275	32	0.984	0.932	0.939	0.896	0.961
USG <1.013 (n=510)	20	490
UCol ⩾4 (n=445)	259	186	0.878	0.643	0.728	0.582	0.903
UCol <4 (n=371)	36	335

^aSensitivity: Percentage of true positives (that is, U_Osm >500 mOsm/kg) detected by U_SG ⩾1.013 or U_Col ⩾4.

Specificity: Percentage of true negatives (that is, U_Osm ⩽500 mOsm/kg) detected by U_SG <1.013 or U_Col <4.

Accuracy: Percentage of all samples (positive or negative) accurately classified by U_SG or U_Col.

Positive predictive value (PPV): Probability that a urine sample with U_SG ⩾1.013 or U_Col ⩾4 has a U_Osm >500 mOsm/kg.

Negative predictive value (NPV): Probability that a urine sample with U_SG <1.013 or U_Col <4 has a U_Osm ⩽500 mOsm/kg.