Table 3.

Diagnostic performance of biochemical tests and extravascular body fluid criteria for NSTI using soft tissue infectious fluids

	AUC	95% CI	p value	Optimal cut-off-point	Sensitivity	Specificity	PPV	NPV	LR +	LR-
Biochemical tests
Albumin (fluid) (g/dL)	0.884	0.790–0.978	< 0.001*	1.25	81.6%	91.3%	93.9%	75.0%	9.4	0.2
Lactate (fluid) (mg/dL)	0.891	0.808–0.973	< 0.001*	64.25	75.7%	100.0%	100.0%	71.0%	–	0.2
Lactate dehydrogenase (fluid) (U/L)	0.955	0.910–1.001	< 0.001*	493.85	86.8%	91.3%	94.3%	80.8%	10.0	0.1
Glucose (fluid) (mg/dL)	0.774	0.654–0.894	< 0.001*	109.5	71.4%	82.6%	86.2%	65.5%	4.1	0.3
Total protein (fluid) (g/dL)	0.883	0.789–0.977	< 0.001*	1.95	86.5%	91.3%	94.1%	80.8%	9.9	0.1
pH (fluid)	0.780	0.654–0.906	< 0.001*	8.4	69.4%	70.0%	80.6%	56.0%	2.3	0.4
Common extravascular body fluid criteria
Light’s criteria (at least one criterion met)	0.737	0.580–0.893	0.003*	> 0	100.0%	47.4%	77.3%	100.0%	1.9	0.0
Light’s criteria (total score)	0.925	0.847–1.003	< 0.001*	> 2	85.3%	94.7%	96.7%	78.3%	16.1	0.2
Serum-to-fluid albumin gradient (g/L)	0.881	0.800–0.963	< 0.001*	2.00	70.3%	91.3%	92.9%	65.6%	8.1	0.3
Fluid-to-serum LDH ratio	0.929	0.865–0.993	< 0.001*	1.51	91.7%	81.8%	89.2%	85.7%	5.0	0.1
Fluid-to-serum total protein ratio	0.927	0.858–0.996	< 0.001*	0.47	88.2%	89.5%	93.8%	81.0%	8.4	0.1

(1) The optimal cutoff points were determined using the Youden index. (2) The positive likelihood ratio (LR +) is theoretically infinite when the specificity is 100%

Note: Bold formatting highlights key statistical values (p-values and AUC)

AUC, area under the curve; CI, confidence interval; LDH, lactate dehydrogenase; LR + , positive likelihood ratio; LR − , negative likelihood ratio; NPV, negative predictive value; NSTI, necrotizing soft tissue infection; PPV, positive predictive value

*p < 0.05, considered significant