Final answer:
Malignant hyperthermia is typically diagnosed using the caffeine-halothane contracture test, while diphtheria diagnosis relies on clinical symptoms, vaccination history, and toxin detection through bacterial cultures and immunological techniques like PCR and immunodiffusion.
Step-by-step explanation:
The agents used to determine a definitive diagnosis of malignant hyperthermia (MH) are not directly listed in the provided information, which instead pertains to diphtheria diagnosis. The standard test for MH is the caffeine-halothane contracture test (CHCT), which is conducted on a biopsy of skeletal muscle. To diagnose diphtheria, clinical symptoms, such as the appearance of a pseudomembrane and vaccination history, are initially considered. Confirmation of diphtheria involves identifying bacterial cultures from throat swabs and detecting the diphtheria toxin using techniques like PCR, radial immunodiffusion, or Elek's immunodiffusion test.