Anemia Raises Risk for Acute Kidney Injury, Poorer Recovery

Daniel M. Keller, PhD

November 14, 2014

PHILADELPHIA — Anemia raises the risk for acute kidney injury in hospitalized patients, new research shows.

In addition, "we've noticed that as the severity of anemia increases, the risk of acute kidney injury increases," said Melanie Godin, MD, from the University of California, San Diego (UCSD) Medical Center.

These findings, from two studies of a cohort of patients from the UCSD Medical Center, were presented here at Kidney Week 2014.

Anemia, defined as a hemoglobin level below 10 g/dL, is recognized as a modifiable risk factor for acute kidney injury in patients undergoing cardiac surgery. However, information has been lacking on the prevalence of anemia in patients hospitalized for medical conditions.

For their studies, Dr Godin and colleagues retrospectively tracked 1946 hospitalized medical patients for 24 months.

The 348 patients with acute kidney injury were significantly older than the 1598 without kidney injury, had a higher body mass index, and had more comorbidities.

Acute kidney injury was defined as a serum creatinine increase of at least 0.3 mg/dL within 48 hours or the need for renal replacement therapy, in accordance with Acute Kidney Injury Network criteria.

Significantly more patients with kidney injury than without had a baseline hemoglobin level below 10 g/dL (51.1% vs 37.9%; P < .001).

At baseline, average hemoglobin level was lower in patients with kidney injury than without (10.2 vs 10.8 g/dL; P < .001). And at all time points during hospitalization, levels of hemoglobin were lower in patients with acute kidney injury. However, hemoglobin levels did not correlate with the severity of the disease.

In a multivariable model, a hemoglobin level below 10 g/dL was demonstrated to be a significant risk factor for acute kidney injury, Dr Godin reported.

Table. Risk Factors Associated With Acute Kidney Injury

Risk Factor Odds Ratio P Value
Heart failure 3.01 <.001
Chronic kidney disease 2.19 <.001
Mean hemoglobin <10 g/dL 1.84 <.001
Diabetes 1.73 <.001
Male 1.72 <.001
Body mass index 1.03 .02
Age 1.01 .02


Patients with pre-existing chronic kidney disease had lower levels of hemoglobin during their hospitalization, but they did not experience an increase in anemia severity. However, the rate of acute kidney injury was worse in patients with chronic disease than in those without (41% vs 15%).

The team also looked at recovery from acute kidney disease in their cohort.

Complete recovery was defined as a ratio of discharge/reference serum creatinine of 1.2 or less, or a difference of less than 0.3 mg/dL between the last and the reference serum creatinine level. A continued need for renal replacement therapy or death was considered to be no recovery, and anything in between was considered to be partial recovery.

Of the 348 patients with acute kidney injury, 69% recovered completely, 23% recovered partially, and 8% did not recover.

Higher mean and baseline hemoglobin levels predicted a full or partial recovery of kidney function. However, there was no association between recovery and other comorbidities, including chronic kidney disease.

Of the patients with chronic kidney disease, 74% recovered completely, 17% recovered partially, and 9% did not recover. In patients who recovered, baseline hemoglobin levels were lower in those with chronic disease than in those without (10.7 vs 11.3 g/dL; P = .04).

The odds of full or partial recovery increased significantly for patients with a hemoglobin level above 10.5 g/dL than for those with a level of 9.24 g/dL or less.

"When you have hemoglobin above 10.5 g/dL, the risk is the same, which is very small," Dr Godin explained. "But as you go below 10.5 g/dL, the risk of not recovering from acute kidney injury increases."

She said the findings need to be tested in other populations of patients.

Susan Quaggin, MD, from the Feinberg Cardiovascular Research Institute at Northwestern University in Chicago, who is chair of the Kidney Week 2014 program committee, said she agrees.

"There's no validation cohort. It would be interesting to see whether or not these findings are validated in another patient population at another center," she told Medscape Medical News. "What would be most interesting is to understand why anemia predicts risk of acute kidney injury or poor recovery. Maybe that will give a clue for prevention."

Does anemia cause acute kidney injury or is the underlying cause of anemia also the cause of kidney injury? "Is anemia a mediator in all of this?" Dr Godin asked. And perhaps a more important question is, "Will the correction of anemia help the situation of acute kidney injury incidence and recovery?" she said.

Dr Quaggin suggested that the correction of anemia might best be addressed using animal models.

Being able to predict renal recovery after acute kidney injury is an important issue, said Dr Quaggin. "There have been a number of studies trying to determine who needs to see a nephrologist after they leave the hospital and how long might they be on dialysis; often it's a very qualitative assessment."

Besides using the creatinine trajectory, "having another equation or another way to predict who's going to recover would be very exciting," she said.

Dr Godin and Dr Quaggin have disclosed no relevant financial relationships.

Kidney Week 2014: American Society of Nephrology Annual Meeting: Abstracts TH-PO002 and TH-PO001. Presented November 13, 2014.


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