Under which condition is LD most likely to be normal?

Lactate dehydrogenase (LDH) is an enzyme found in various tissues throughout the body and serves as a marker for tissue damage. In certain medical conditions, LDH levels can be significantly elevated due to cellular injury and subsequent release of the enzyme into the bloodstream.

Acute appendicitis is characterized by inflammation of the appendix that typically does not lead to extensive tissue necrosis or widespread cellular injury. In this case, the damage is localized, and while there may be some release of LDH, it is generally not sufficient to cause a notable increase in serum levels. Therefore, LDH levels can remain within the normal range in patients with acute appendicitis.

In contrast, conditions like hepatic carcinoma, pulmonary infarction, and crush injury are associated with significant tissue damage. Hepatic carcinoma can cause high elevations in LDH due to liver cell destruction. Pulmonary infarction results in damage to lung tissue, leading to increased LDH. Similarly, crush injuries involve extensive muscle damage, which can also cause a significant increase in LDH levels.

Thus, acute appendicitis is the condition under which LDH is most likely to remain normal, owing to its localized nature and relatively minor systemic effect compared to the other listed conditions.