Table 3.
Nonlinear calcitonin levels due to pseudohook effect of the immunoassay
| Patient | CT (pg/ml), undiluted value | CT (pg/ml) × 5 dilution | CT (pg/ml) fold increase | CT (pg/ml) × 10 dilution | CT (pg/ml) fold increase |
|---|---|---|---|---|---|
| 1 | 1583 | 2774 | 1.8 | 3046 | 1.9 |
| 2 | 1345 | 2923 | 2.2 | 3454 | 2.6 |
| 3 | 1708 | 2167 | 1.3 | 2378 | 1.4 |
| 4 | 418 | 841 | 2.0 | 1084 | 2.6 |
| 5 | 1699 | 2776 | 1.6 | 3184 | 1.9 |
| 6 | 1223 | 1581 | 1.3 | 1685 | 1.4 |
| 7 | 1182 | 1631 | 1.4 | 1750 | 1.5 |
| 8 | 875 | 1166 | 1.3 | 1264 | 1.4 |
| 9 | 455 | 1213 | 2.7 | 1556 | 3.4 |
| 10 | 1169 | 1558 | 1.3 | 1724 | 1.5 |
| 11 | 1736 | 2314 | 1.3 | 2596 | 1.5 |
Eleven representative cases of the 27 patients that showed nonlinear CT levels. Samples were serially diluted until the values of the dilutions match within 20%. Notice the underestimation of CT levels in the undiluted samples.