**Question:** Which of the following is not true regarding radiocontrast media (RCM) reaction?

A. RCM reactions are a result of hypersensitivity reactions to the contrast media or its components.
B. Common RCM reactions include anaphylaxis, anaphylactoid reactions, and non-anaphylactoid reactions.
C. Anaphylactoid reactions are a result of the release of histamine and other mediators from mast cells and basophils.
D. Non-anaphylactoid reactions include delayed reactions, nephrotoxicity, and neurotoxicity.

**Correct Answer:**

D. **Non-anaphylactoid reactions** are not true regarding RCM reactions. Non-anaphylactoid reactions include delayed reactions, nephrotoxicity, and neurotoxicity. However, they are not a separate category of reactions. RCM reactions are primarily classified as anaphylactoid (histamine-mediated) and non-anaphylactoid reactions.

**Why the Correct Answer is Right:**

Radiocontrast media (RCM) reactions are indeed a result of hypersensitivity reactions to the contrast media or its components. These reactions involve the activation of immune cells such as mast cells and basophils, leading to the release of inflammatory mediators like histamine, leukotrienes, and cytokines. These mediators cause the typical symptoms and signs of an allergic reaction, including urticaria, hypotension, bronchospasm, and cardiovascular collapse, which is why we classify RCM reactions as anaphylactoid.

**Why Each Wrong Option is Incorrect:**

A. While RCM reactions can involve hypersensitivity reactions, the statement "RCM reactions are a result of hypersensitivity reactions to the contrast media or its components" is incorrect as it does not specifically address the anaphylactoid reactions.

B. The statement "Common RCM reactions include anaphylaxis, anaphylactoid reactions, and non-anaphylactoid reactions" is misleading. RCM reactions are primarily classified as anaphylactoid reactions (histamine-mediated) or non-anaphylactoid reactions.

C. Anaphylactoid reactions are indeed caused by histamine release from mast cells and basophils, resulting in symptoms like bronchospasm, hypotension, and cardiovascular collapse. Anaphylactoid reactions are the most common and severe type of RCM reactions.

E. Non-anaphylactoid reactions include delayed reactions, nephrotoxicity, and neurotoxicity. While these reactions are related to RCM use, they are separate from anaphylactoid reactions and can occur at different time points after administration.

**Clinical Pearls:**

1. RCM reactions are anaphylactoid reactions involving histamine release or non-anaphylactoid reactions related to nephrotoxicity, neurotoxicity, and delayed reactions. Understanding the distinction between anaphylactoid reactions and non-anaphylactoid reactions is crucial for clinical practice and patient management.