TABLE 1.

Tests and reference preparations for participant laboratories

LaboratoryAssayLowest level of detection (IU/ml)Diphtheria toxin or toxoid, producer (Lf)aDiphtheria reference serum (antitoxin)b
IdDA-DELFIA0.0004Toxoid, SSI (2,267/ml)WHO,c batch DI98 (equine)
ELISA (VaccZyme)0.012ToxoidNIBSC, batch 00/496 (human)
ELISA (Virotech)0.1dToxoidNIBSC, batch 00/496 (human)
IIPHA0.01ToxinControl serum, 10 IU/ml
IIIELISA (in-house method)0.001Toxoid, NCIPD Sofia (490/ml)In-house human serum calibrated against WHO standardb
IVELISA (VaccZyme)0.012ToxoidNIBSC, batch 00/496 (human)
ELISA (NovaLisa)0.01ToxoidNIBSC, batch 91/534 (human)
VELISA (Virotech)0.1dToxoidNIBSC, batch 00/496 (human)
VIELISA (VaccZyme)0.012ToxoidNIBSC, batch 00/496 (human)
Vero cell (NT)0.016Toxin, RIVM batch 79/1 (1,000/ampoule)NIBSC 3rd British standard, batch 66-153 (equine)
VIIELISA (Euroimmun)0.005ToxoidNIBSC, batch 91/534 (human)
VIIIVero cell (NT)0.004Toxin; Japanese, lot M59 (0.25/ml)JNSDAe (equine)
IXfDAE0.007ToxoidWHO,c batch DI05 (equine)
ELISA (VaccZyme)0.012ToxoidNIBSC, batch 00/496 (human)
Vero cell (NT)0.005Toxin, KTL (650/ml)WHO,c batch DI05 (equine)
XELISA (Serion)0.05ToxoidSSIc
XIELISA (in-house method)0.015ToxoidgNIBSC, batch 00/496 (human)
Vero cell (NT)0.0008Toxin, EDQM, BRP batch 1WHO,c batch DI07 (equine)
XIIToBI0.005Toxin, 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).