Table 1.
Operating characteristics of the CLIA vs 2 other commercial PF4-dependent EIAs (one performed with the high-heparin step)
| CLIA (95% CI) | EIA-IgG with high-heparin step (95% CI) P value (vs CLIA) | EIA-IgG without high-heparin step (95% CI) P value (vs CLIA) | EIA-IgGAM without high-heparin step (95% CI) P value (vs CLIA) | |
|---|---|---|---|---|
| Se | 32/33 = 97.0% (84.2%, 99.9%) | 32/33 = 97.0% (84.2%, 99.9%) P = 1.0 | 33/33 = 100% (89.4%, 100%) P = .3173 | 33/33 = 100% (89.4%, 100%) P = .3173 |
| Se* | 166/168 = 98.8% (95.7%, 99.8%) | 162/168 = 96.4% (92.4%, 98.7%) P = 0.1573 | 167/168 = 99.4% (96.7%, 100.0%) P = .5637 | 168/168 = 100% (97.83%, 100.1%) P = .1573 |
| Sp | 469/476 = 98.5% (97.0%, 99.4%) | 448/476 = 94.1% (91.6%, 96.1%) P < .0001 | 435/476 = 91.4% (88.5%, 93.7%) P < .0001 | 393/476 = 82.6% (78.8%, 85.9%) P < .0001 |
| PPV | 32/39 = 82.1% (66.5%, 92.5) | 32/60 = 53.3% (40.0%, 66.3%) P < .0001 | 33/74 = 44.6% (33.0%, 56.6%) P < .0001 | 33/116 = 28.5% (20.5%, 37.6%) P < .0001 |
| NPV | 469/470 = 99.8% (98.8%, 99.99%) | 448/449 = 99.8% (98.8%, 99.99%) P = .9742 | 435/435 = 100% (99.2%, 100%) P = .3168 | 393/393 = 100% (99.1%, 100%) P = .3167 |
| LR+ | 65.9 (31.5, 137.9) | 16.5 (11.5, 23.7) P = .0002 | 11.6 (8.6, 15.6) | 5.7 (4.7, 7.0) |
| LR− | 0.031 (0.004, 0.212) | 0.032 (0.005, 0.222) P = .9742 | 0.0 (undefined) | 0.0 (undefined) |
| AUC | 0.997 (0.994, 1.000) | 0.994 (0.985, 1.000) P = .4016 | 0.997 (0.994, 1.000) P = .7225 | 0.992 (0.986, 0.999) P = .1053 |
The table presents the results of 3 different PF4-dependent immunoassays (including 1 assay, the EIA-IgG, performed with and without the high-heparin step) tested on 509 patients (33 SRA-positive) from a prospective study of the 4Ts scoring system.8 All samples tested were sera, with the exception of 2 plasma samples tested in the EIA-IgGAM (without high heparin). CLIA results using plasma are as follows: for 429 of the 509 patients, citrated plasma was available for testing in the CLIA, with the following operating characteristics found: (1) sensitivity = 30/31 (96.8%; 95% CI, 83.3%, 99.9%); (2) sensitivity (including 135 consecutive HIT-positive patients from one hospital) = 162/166 (97.6%; 95% CI, 93.9%, 99.3%); (3) specificity = 391/398 (98.2%; 95% CI, 96.4%, 99.3%); (4) PPV = 30/37 (81.1%; 95% CI, 64.8%, 92.0%); (5) NPV = 391/392 (99.7%; 95% CI, 98.6%, 100%); (6) LR+ = 55.0 (95% CI, 26.3, 115.0); and (7) LR− = 0.033 (95% CI, 0.005, 0.226). All comparisons were not significantly different than the results seen with serum (P ≥ .3120 for all 6 comparisons).
AUC, area under the curve; EIA-IgG, enzyme immunoassay (IgG specific); EIA-IgGAM, enzyme immunoassay (polyspecific); Se, sensitivity; Sp, specificity.
Sensitivity calculations performed with the addition of 135 consecutive HIT-positive patients from one hospital (total HIT-positive patients, n = 168), identified from February 1999 until January 2018, inclusive.