Table 3.

Sensitivities (Se), specificities (Sp), and correlations for measurements of IgG concentration in different studies with digital and optical refractometers in comparison to the gold standard.

Refractometer	Standard	Se	Sp	Correlation	R2	Special Features	Source
Digital Optical	RID	0.93	0.80	0.73 *	0.53	fresh colostrum for Se and Sp frozen colostrum for correlation	[20] 1
		0.91	0.85	0.71 *	0.51
Digital Optical	RID	0.79	0.69	n. d.	n. d.	Incubated in water baths to maintain the optimum temperature	[10] 1
		0.56	0.90
Digital Optical	RID	0.82	0.81	0.60 *	n. d.	n. d.	[5] 1
		0.80	0.83	0.60 *
Digital Optical	RID	0.74	0.80	0.72 *	n. d.	frozen colostrum	[11] 1
		0.73	0.80	0.71 *
Digital Optical	RID	1.00	0.66	0.74	n. d.	frozen and unheated colostrum	[42] 1
		1.00	0.63	0.73
Digital	RID	0.97	0.61	0.75		frozen and heated at 60 °C for 30 min
Optical		0.97	0.65	0.73
Digital Optical	RID	0.97	0.65	0.71		frozen and heated at 60 °C for 60 min
		0.97	0.68	0.70
Digital Optical	RID	0.90	0.38	0.48		frozen and heated at 63 °C for 30 min
		0.90	0.38	0.50
Digital Optical	RID	0.88	0.39	0.58		frozen and heated at 63 °C for 60 min
		0.88	0.39	0.57
Digital	RID	0.75	0.78	n. d.	0.41	fresh colostrum for refractometer frozen colostrum for the RID	[1] 1
Digital	RID	0.66	0.83	0.64	0.43	frozen colostrum	[7] 1
Digital	RID	1.00	0.65	n. d.	n. d.	fresh colostrum for refractometer frozen colostrum for the RID	[53] 1
Digital	RID	0.84	0.79	0.71 *	n. d.	frozen colostrum	[45] 1
Digital	RID	0.84	0.79	0.68–0.76	n. d.	frozen colostrum	[54] 2
Optical	RID	0.93	0.66	0.75 **	0.56	frozen colostrum	[8] 1
Optical	ELISA	0.86	0.85	n. d.	0.43	frozen colostrum for ELISA n. d. for refractometer	[31] 1

n. d. = no data; R² = coefficient of determination; ¹ Cut-off point of ≥50 mg IgG mL⁻¹ for colostrum of good quality; ² Cut-off point of ≥150 mg IgG mL⁻¹ for colostrum of good quality; * p < 0.001; ** p < 0.01.