**Question:** Following is given in case of pernicious anaemia?

A. Hypotension
B. Hypothyroidism
C. Hypoalbuminemia
D. Hyponatremia

**Core Concept:** Pernicious anaemia is a type of vitamin B12 deficiency anaemia characterized by impaired red blood cell production and neurological symptoms. It is caused by a deficiency of intrinsic factor, a glycoprotein secreted by parietal cells in the stomach, which is necessary for the absorption of vitamin B12 in the ileum.

**Why the Correct Answer is Right:** The correct answer is **D.** Hyponatremia, which refers to low serum sodium levels, can be seen in pernicious anaemia due to the following reasons:

1. Impaired red blood cell production: Pernicious anaemia leads to a decrease in red blood cell mass, resulting in lower oxygen-carrying capacity, which can cause tissue hypoxia and stimulate the release of antidiuretic hormone (ADH) from the hypothalamus.
2. Decreased renal sodium and water excretion: ADH promotes water reabsorption and inhibits sodium excretion in the kidneys, leading to increased water reabsorption and decreased sodium excretion. This results in a decrease in serum sodium levels.
3. Increased renal tubular permeability: The impaired red cell production leads to decreased red cell mass, and the kidneys compensate by increasing their permeability to water, which further contributes to hyponatremia.

**Why Each Wrong Option is Incorrect:**

A. Hypotension: Though hypotension can be present in severe cases of pernicious anaemia, the correct answer is hyponatremia due to the reasons mentioned above.

B. Hypothyroidism: Pernicious anaemia is not related to thyroid hormones or hypothyroidism, so this option is incorrect.

C. Hypoalbuminemia: Hypoalbuminemia is a decrease in serum albumin levels, while the correct answer is hyponatremia due to the reasons mentioned above.

**Clinical Pearl:** Hyponatremia is a crucial finding in pernicious anaemia, which is often overlooked by physicians due to its non-specific presentation. It can be a valuable clue in diagnosing this condition, alongside other clinical and laboratory findings. Early detection and treatment of pernicious anaemia are crucial to prevent severe complications such as cerebral oedema and seizures.