HDCN Article Review/Hyperlink

Sklar AH, Riesenberg LA, Ur Rehman A, Smith S, Rivera-Padilla H

Prerenal azotemia: differentiation or hyperureagenesis from renal hypoperfusion using urea nitrogen data

Int J Artif Organs (Mar) 19:164-169 1996

The patient with a high serum BUN/creatinine ratio is a common clinical problem, and suggests prerenal azotemia. However, increased urea generation due to hypercatabolism (steroids, tetracycline, GI bleeding) can present with a similar picture. In the present study, the authors theorized that in states of "hyperureagenersis", urea production rates should be greatly increased, and therefor 24 hour urea excretion rates should be unusually high.

They studied 27 patients in whom the serum BUN was increasing, im whom the BUN was at least 30 mg/dl (11 mmol/L), and in whom the BUN/creatinine ratio was at least 20:1. The charts were reviewed, and patients were assigned to either a renal hypoperfusion group, or to a hyperureagenesis group bases on clinical criteria, including response to fluid therapy. This assessment was done by a nephrologist blinded to the urinary urea indices. PCR was assessed from the urea generation rate, which included the increase in BUN. If observed PCR was greater than 10 gm higher than dietary protein intake, patients were considered hypercatabolic.

Fractional excretion of urea nitrogen (FEUN %) was calculated as follows:

FEUN (%) = (UUN/BUN) divided by (Urine Cr/Serum Cr) x 100

The patients had similar predialysis BUN levels (mean 63-78 mg/dl) and BUN/creatinine ratios (mean 36-39). In the clinically designated hypoperfusion group, 12/17 had heart failure, 4/17 volume depletion, and 1/17 hepatorenal syndrome. In the hyperureagenesis group, 5/10 where on steroids, and 3/10 had high protein intake, 1/10 had sepsis, and 1/10 had tumor lysis syndrome.

Creatinine clearance averaged 21 ml/min in the hypoperfusion group and 36 in the hyperureagenesis group. Urinary sodium was 39 and 45 meq/L, FENa was not calculated. These patients were not oliguric, with mean volumes of 1094 and 1853 ml/day in the hypoperfusion and hyperureagenesis groups, respectively. Calculated 24 h UUN excretion was 6.6 gm/day in the hypoperfusion group and 13.1 in the hyperureagenesis group, with FEUN values of 24 +/1 12 and 38 +/1 12, respectively. Protein catabolic rates averaged 54 and 111 gm/24 hours in the two groups.

Comment: The data are interesting and should be correct. The usefulness of these measurements is somewhat questionable, as one will usually know if a patient is on steroids or eating inordinately large amounts of protein or septic. Also, there are patients clinically who have both hypoperfusion (heart failure) and who are on steroids. The patients studied were not oliguric, and it is unclear how this data would help the clinician decide if fluid adiministration is indicated. (John T. Daugirdas, M.D., University of Illinois at Chicago)