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Table 5 ROC-analysis: Relative accuracies of PrioCHECK ® Toxoplasma Ab SR ELISA (cut-off PP 20) in relation to IFAT, IHA and real-time PCR

From: Evaluation of a commercial ELISA kit for detection of antibodies against Toxoplasma gondii in serum, plasma and meat juice from experimentally and naturally infected sheep

    PrioCHECK® Toxoplasma Ab SR ELISA
Reference test Sample AUC/P* Selected cut-off in ELISA % relative sensitivity (95% confidence interval) % relative specificity (95% confidence interval)
A
IFAT (cut-off 1:40) serum 1.000/<0.000 19.79 100 (81.5 - 100.0) 100 (95.4 – 100.0)
IFAT (cut-off 1:80) serum 1.000/<0.000 19.79 100 (81.5 - 100.0) 100 (95.4 – 100.0)
IHA (cut-off 1:80) serum 1.000/<0.000 19.79 100 (81.5 - 100.0) 100 (95.4 – 100.0)
Real-time PCR brain/muscle 0.959/<0.0001 19.79 100 (71.5 - 100.0) § 91.76 (83.8 - 96.6)§
IFAT (cut-off 1:40) meat juice 1:10** 0.999/<0.0001 20.29 100 (81.5 - 100.0) 98.72 (93.1 - 100.0)
IFAT (cut-off 1:80) meat juice 1:10** 0.996/<0.0001 27.64 100 (78.2 - 100.0) 97.53 (91.4 - 99.7)
IFAT (cut-off 1:40) meat juice 1:20** 0.999/<0.0001 15.83 100 (81.5 - 100.0) 98.72 (93.1 - 100.0)
IFAT (cut-off 1:80) meat juice 1:20** 0.998/<0.0001 27.45 100 (78.2 - 100.0) 98.77 (93.3 - 100.0)
B      
IFAT (cut-off 1:40) serum 0.991/<0.0001 17.24 93.33 (88.1 - 96.8) 98.67 (95.3 - 99.8)
IFAT (cut-off 1:80) serum 0.985/<0.0001 21.05 96.43 (91.9 - 98.8) 96.87 (92.9 - 99.0)
IHA (cut-off 1:80) serum 0.998/<0.0001 21.05 97.87 (93.9 - 99.6) 98.74 (95.5 - 99.8)
  1. A: Tests performed with samples from Swiss sheep (Group 2), B: Tests performed with samples from Austrian sheep (Groups 3 and 4).
  2. *Significance level P (Area = 0.5); ** meat juice dilution; AUC: Area under curve.
  3. § Note: The apparent low specificity of ELISA when real-time PCR is taken as reference test might be related to the low diagnostic sensitivity of PCR techniques linked to the small size of the analyzed sample. All real-time PCR positive animals were recognized as positive by ELISA (100% relative sensitivity), but some serologically positive animals in ELISA had negative PCR results accounting for a (potentially erroneous) relative lower specificity of the ELISA.