You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Fractional excretion of sodium (FENa) is calculated as and explain in detail?
The fractional excretion of sodium (FeNa) is the fraction of the filtered sodium load that is reabsorbed by the tubules FENa relates sodium clearance to creatinine clearance. As such, it depends on sodium intake, effective intravascular volume, GFR, diuretic intake, and intact tubular reabsorptive mechanisms. With prerenal azotemia, the FeNa may be below 1%, suggesting avid tubular sodium reabsorption. FENa may be >1.0% in prerenal ARF if patients are on diuretics or with pre-existing CKD, salt-wasting syndromes or adrenal insufficiency. Ref: Harrison 19e 1807