Table 3.
Optimal cutoff values and performance of diagnostic measures
| Diagnostic measure | Optimal cutoff values | Sensitivity* | Specificity* | PPV* | NPV* | Accuracy* | AUC | p value for AUC |
|---|---|---|---|---|---|---|---|---|
| ESR (n = 131) | 32 mm/hr | 83% (77%–90%) | 82% (76%–89%) | 43% (34%–51%) | 97% (94%–100%) | 82% (76%–89%) | 88% | N/A |
| CRP (n = 129) | 10 mg/L | 94% (90%–98%) | 78% (70%–85%) | 39% (31%–47%) | 99% (97%–100%) | 80% (73%–87%) | 85% | N/A |
| Synovial fluid WBC count | 0.1013 | |||||||
| Before exclusion of inaccurate samples (n = 141) | 3111 cells/μL | 94% (90%–98%) | 86% (80%–92%) | 50% (41%–59%) | 99% (97%–100%) | 87% (81%–93%) | 89% | |
| After exclusion of inaccurate samples (n = 102)† | 4350 cells/μL | 100% (100%–100%) | 95% (90%–99%) | 69% (60%–78%) | 100% (100%–100%) | 95% (91%–99%) | 98% | |
| %PMN | 0.8826 | |||||||
| Before exclusion of inaccurate samples (n = 112) | 85% | 85% (78%–91%) | 86% (80%–93%) | 46% (36%–55%) | 98% (95%–100%) | 86% (80%–93%) | 90% | |
| After exclusion of inaccurate samples (n = 102)‡ | 85% | 82% (74%–89%) | 87% (80%–93%) | 43% (33%–52%) | 98% (95%–100%) | 86% (79%–93%) | 90% | |
* Ninety-five percent confidence intervals in parentheses; †n reflects 39 synovial fluid samples excluded (from 141 samples originally available for review) for inaccuracy secondary to metal debris, fragmented cells, etc, as described in Materials and Methods; ‡n reflects 10 synovial fluid samples excluded (from 112 samples originally available for review with a differential) for inaccuracy secondary to metal debris, fragmented, cells, etc, as described in Materials and Methods; PPV = positive predictive value; NPV = negative predictive value; AUC = area under the receiver operator curve; ESR = erythrocyte sedimentation rate; CRP = C-reactive protein; WBC = white blood cell; %PMN = percentage polymorphonuclear cells; N/A = not applicable.