The anemia of acute renal failure: association with oliguria and elevated blood urea.

Anemia is very frequent in patients with acute failure but the nature of the relationship between the two conditions has remained unclear. We studied all patients with well-documented acute renal failure seen in consultation by our nephrology division during 1991. Fifty-three of the 56 patients had at least mild anemia (hematocrit < 35%) at some point during their hospital stay. Forty-three of the patients had a hematocrit below 30% and 14 had a hematocrit below this level on admission. Twenty-four of the patients underwent major operations and all of these patients required blood transfusions. In this group there was a significant correlation between maximum serum urea and lowest hemoglobin (r = 0.4, p < .05) but no similar correlation between maximum creatinine and lowest hemoglobin. Oliguric patients had a mean lowest hemoglobin of 7.3 +/- 0.4 g/dL, which was significantly lower than the value for nonoliguric patients, 9.0 +/- 0.4 g/dL. This study confirms the presence of anemia in 91% of patients with acute renal failure and shows it to be related to rise in urea and presence of oliguria. Clearly, however, the anemia is multifactorial, since in one-quarter of the patients it precedes onset of renal failure.