Which of the following is not quantified using an immunoassay method?

• A. Vitamins
• B. Hormones
• C. Electrolytes
• D. Drugs

Answer: (C)

Immunoassay methods quantify substances through antibody binding to the target molecule, allowing very sensitive and specific detection in biological fluids. This approach works well for molecules that antibodies can recognize reliably, such as vitamins and hormones, as well as many drugs, which is why these categories are commonly measured with immunoassays. Electrolytes, however, are inorganic ions (like sodium, potassium, chloride) and are detected by chemistry-based techniques that measure ion activity or concentration directly—often with ion-selective electrodes, flame photometry, or other electrochemical methods. Because they are not typically identified by antibody-antigen interactions, electrolytes are not quantified using immunoassay methods.