Final answer:
The most likely diagnosis for an old man with abdominal bruit and elevated renin levels is renal artery stenosis, which leads to increased renin release due to reduced blood flow to the kidneys and is diagnosed with imaging and lab tests.
Step-by-step explanation:
The most likely diagnosis for an old man presenting with abdominal bruit and elevated levels of renin, angiotensin I (A1), and angiotensin II (A2) is 1) Renal artery stenosis. This condition is characterized by the narrowing of the renal arteries, which can lead to high blood pressure and kidney damage due to limited blood flow to the kidneys. An abdominal bruit is typically heard through a stethoscope and is indicative of turbulent blood flow, often associated with stenosis. Elevated renin levels occur as the kidneys respond to perceived low blood pressure by releasing renin, which activates the renin-angiotensin system to increase blood pressure. This contrasts with other potential diagnoses such as renal cell carcinoma, renal vein thrombosis, and renal cysts, which commonly do not elevate renin levels in the same manner as renal artery stenosis.
Renal artery stenosis leads to an increase in renin release due to reduced renal perfusion. Appropriate diagnostic imaging, such as Doppler ultrasound or magnetic resonance angiography (MRA), and lab tests confirming high plasma renin activity, are often used in conjunction with the patient's clinical presentation to make a definitive diagnosis.