TABLE 1.
Tests and reference preparations for participant laboratories
| Laboratory | Assay | Lowest level of detection (IU/ml) | Diphtheria toxin or toxoid, producer (Lf)a | Diphtheria reference serum (antitoxin)b |
|---|---|---|---|---|
| I | dDA-DELFIA | 0.0004 | Toxoid, SSI (2,267/ml) | WHO,c batch DI98 (equine) |
| ELISA (VaccZyme) | 0.012 | Toxoid | NIBSC, batch 00/496 (human) | |
| ELISA (Virotech) | 0.1d | Toxoid | NIBSC, batch 00/496 (human) | |
| II | PHA | 0.01 | Toxin | Control serum, 10 IU/ml |
| III | ELISA (in-house method) | 0.001 | Toxoid, NCIPD Sofia (490/ml) | In-house human serum calibrated against WHO standardb |
| IV | ELISA (VaccZyme) | 0.012 | Toxoid | NIBSC, batch 00/496 (human) |
| ELISA (NovaLisa) | 0.01 | Toxoid | NIBSC, batch 91/534 (human) | |
| V | ELISA (Virotech) | 0.1d | Toxoid | NIBSC, batch 00/496 (human) |
| VI | ELISA (VaccZyme) | 0.012 | Toxoid | NIBSC, batch 00/496 (human) |
| Vero cell (NT) | 0.016 | Toxin, RIVM batch 79/1 (1,000/ampoule) | NIBSC 3rd British standard, batch 66-153 (equine) | |
| VII | ELISA (Euroimmun) | 0.005 | Toxoid | NIBSC, batch 91/534 (human) |
| VIII | Vero cell (NT) | 0.004 | Toxin; Japanese, lot M59 (0.25/ml) | JNSDAe (equine) |
| IXf | DAE | 0.007 | Toxoid | WHO,c batch DI05 (equine) |
| ELISA (VaccZyme) | 0.012 | Toxoid | NIBSC, batch 00/496 (human) | |
| Vero cell (NT) | 0.005 | Toxin, KTL (650/ml) | WHO,c batch DI05 (equine) | |
| X | ELISA (Serion) | 0.05 | Toxoid | SSIc |
| XI | ELISA (in-house method) | 0.015 | Toxoidg | NIBSC, batch 00/496 (human) |
| Vero cell (NT) | 0.0008 | Toxin, EDQM, BRP batch 1 | WHO,c batch DI07 (equine) | |
| XII | ToBI | 0.005 | Toxin, RIVM batch 79/1 (1,000/ampoule) | WHO,c batch DI07 (equine) |
a
Lf, limit of flocculation.
b
In the case of ELISA, the reference serum is the one against which the human sera used as control in the kit have been calibrated.
c
Since 1997, the diphtheria antitoxin WHO 1st international standard (Statens Serum Institut, Copenhagen, Denmark) (10 IU/ml) has been distributed by the National Institute for Biological Standards and Control (NIBSC) in different liquid lots with the prefix “DI.”
d
Limit of quantification.
e
JNSDA, Japanese National Standard Diphtheria.
f
Reference laboratory.
g
2nd WHO International Standard for diphtheria toxoid (NIBSC code 02/176, 1,100 Lf/ampoule) for coating plates (at 0.5 Lf/ml).