Creatinine Increase Post-Cardiac Surgery Linked to Long-Term Kidney Disease

February 23, 2011

February 23, 2011 (Minneapolis, Minnesota) — Even small increases in serum creatinine levels after cardiac surgery are associated with long-term renal complications, a new study shows [1].

The study, published in the February 14, 2011 issue of the Archives of Internal Medicine, found a graded association between the magnitude of creatinine increase after cardiac surgery and an increased risk of incident chronic kidney disease, progression of kidney disease, and death.

The authors, led by Dr Areef Ishani (Minneapolis Veterans Affairs Health Care System, Minnesota), explain that acute kidney injury is common among patients undergoing cardiac surgery and is known to be associated in the short term with increased hospital stay, risk for infection, hospital expenditures, and mortality. But it has been assumed that if an individual survived an episode of acute kidney injury, there were no long-term sequelae. This assumption has been recently challenged by studies suggesting an association between acute kidney injury and increased risk of mortality and end-stage kidney disease, although further data are needed.

To look at this issue, Ishani et al examined whether the magnitude of creatinine increase after cardiac surgery was linked to long-term outcomes in 29 388 individuals who underwent surgery at Veterans Affairs hospitals between 1999 and 2005.

The magnitude of creatinine increase was defined by the percentage change from baseline to peak creatinine levels after cardiac surgery and categorized as none (<0%), class I (1%-24%), II (25%-49%), III (50%-99%), or IV (>100%).

After adjustment using Cox proportional hazard models, results showed that incident chronic kidney disease, progression of kidney disease, and death all increased with greater increases in creatinine levels, with the risks significantly higher immediately after the creatinine increase and attenuating over time.

Results at Three Months: Hazard Ratios for Outcomes Related to Creatinine Increase by Class

Outcome

Class I

Class II

Class III

Class IV

Incident chronic kidney disease 

2.1

4.0

5.8

6.6

Progression of kidney disease

2.5

3.8

4.4

8.0

Death

1.4

1.9

2.8

5.0

Results at Five Years: Hazard Ratios for Outcomes Related to Creatinine Increase by Class

Outcome

Class I

Class II

Class III

Class IV

Incident chronic kidney disease 

1.4

1.9

2.3

2.3

Progression of kidney disease

1.5

1.7

1.7

2.4

Death

1.0

1.2

1.4

1.8

The researchers say their results have significant clinical implications. But they point out that currently, few individuals with acute kidney injury see a nephrologist and many do not have follow-up serum creatinine measurements. They recommend that future research should develop strategies to prevent acute kidney injury or long-term sequelae associated with such injury, particularly in the first three to 24 months.

In an accompanying editorial [2], Drs Neesh Pannu and Brenda Hemmelgarn (Alberta Kidney Disease Network, Edmonton) point out that while the incidence of acute kidney injury requiring renal replacement therapy after cardiac surgery remains relatively low (around 2%), up to 40% of patients develop lesser degrees of acute kidney injury, and subtle markers of renal injury are detectable in urine samples from virtually all patients undergoing cardiopulmonary bypass.

They say that the current findings, which suggest that any change in kidney function after cardiac surgery has significant effects on kidney function over the long term, underscore the challenges in both identifying and defining kidney injury. And the notion that all clinically relevant kidney injury can be captured using standardized diagnostic criteria must continue to be examined.

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