Which of the following is NOT a cause of hypovolaemic hyponatraemia?

Hypovolaemic hyponatraemia refers to a condition where there is a low concentration of sodium in the blood due to a decrease in blood volume. In this context, understanding the underlying causes that can lead to such a condition is important.

Fluid loss, which can occur from a variety of sources such as excessive sweating, vomiting, or diarrhea, directly reduces blood volume and can contribute to hyponatraemia. Similarly, Addison's disease interferes with the adrenal glands' ability to produce adequate levels of cortisol and aldosterone, which are hormones that help regulate sodium and fluid balance. Diuretics also contribute to hypovolaemic hyponatraemia by promoting the excretion of sodium and water from the kidneys, leading to a reduction in blood volume.

In contrast, liver failure is typically associated with a different mechanism. While liver failure can lead to fluid accumulation in the abdominal cavity (ascites) and can affect sodium levels, it generally causes hypervolemic or euvolemic hyponatraemia instead of hypovolaemic hyponatraemia. This scenario arises because liver failure often leads to an increase in total body water despite a relative deficiency in sodium levels, rather than a true loss of volume as seen in the other conditions