What lab abnormality is commonly associated with fibromuscular dysplasia (FMD)?

Fibromuscular dysplasia (FMD) is a vascular condition that affects the arteries, most commonly the renal arteries, leading to stenosis (narrowing) and, subsequently, renal artery hypertension. One of the key lab abnormalities observed in patients with renal artery stenosis due to FMD is increased renin levels. This occurs as a result of decreased renal perfusion pressure.

When the renal arteries are narrowed, the kidney senses a drop in blood flow, which stimulates the juxtaglomerular cells of the kidney to secrete renin. Renin is an enzyme that plays a crucial role in the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and fluid balance. As renin levels rise, it leads to an increase in angiotensin II, which causes vasoconstriction and further exacerbates hypertension.

In summary, increased renin is the lab abnormality that is most commonly associated with fibromuscular dysplasia due to the mechanisms of renal artery stenosis and the body's compensatory response to perceived low blood flow to the kidneys.