Table 2.

Optimal criteria (cut point) in 72 calves with neonatal calf diarrhea (NCD) determined by receiver operating characteristic (ROC) curves for assessing the failure of transfer of passive immunity (FTPI) for serum total protein concentration (STP) in both normohydrated and dehydrated patients and gamma-glutamyl-transferase activity (GGT) in calves with age > 3 days, using three different cut-off points (serum immunoglobulin G concentration < 10 g/L, 18 g/L, and 25 g/L)

Cut-off value for diagnosing FTPI	Classification variable	N	J	Cut point	AUC	CI 95%
IgG: 10 g/L	STP in normohydrated calves	18	0.75	56 g/L	0.92	0.70-1.00
	STP in dehydrated calves	54	0.59	56 g/L	0.82	0.70–0.92
	GGT in calves with age > 3 days	61	0.78	124 IU/L	0.94	0.84–0.98
	GGT in normohydrated calves > 3 days	15	0.90	147 IU/L	0.92	0.66-1.00
	GGT in dehydrated calves > 3 days	46	0.88	100 IU/L	0.95	0.84–0.95
IgG: 18 g/L	STP in normohydrated calves	18	0.75	56 g/L	0.92	0.69–0.99
	STP in dehydrated calves	54	0.37	65 g/L	0.73	0.59–0.84
	GGT in calves with age > 3 days	61	0.58	147 IU/L	0.80	0.68–0.89
	GGT in normohydrated calves > 3 days	15	0.67	147 IU/L	0.85	0.58–0.98
	GGT in dehydrated calves > 3 days	46	0.55	142 IU/L	0.80	0.65–0.90
IgG: 25 g/L	STP in normohydrated calves	18	1.00	60 g/L	1.00	0.82-1.00
	STP in dehydrated calves	54	0.38	75 g/L	0.74	0.60–0.85
	GGT in calves with age > 3 days	61	0.51	147 IU/L	0.77	0.65–0.87
	GGT in normohydrated calves > 3 days	15	0.62	185 IU/L	0.73	0.44–0.92
	GGT in dehydrated calves > 3 days	46	0.54	142 IU/L	0.79	0.64–0.91

AUC, area under the curve; CI 95%, 95% confidence interval; J, Youden index (J = Sensitivity + Specificity – 1)