Acute Kidney Injury: A Harbinger of Other Illnesses?

Does acute kidney injury predict later health problems? And, do the kidneys completely recover?

Since my first goal in this venue is to focus on primary care issues, I avoid overemphasizing nephrology. But, in my role as a subspecialist, I have been asked two questions repeatedly. First, does acute kidney injury (AKI) predict other problems later? Second, does AKI always recover completely? Recent studies may provide answers.

QUESTION NO. 1: THE PREDICTIVE POWER OF ACUTE KIDNEY INJURY

Thirty-six articles were chosen, attempting to answer the first question; 13 were included for a systematic study.1 Eleven of the studies totaled 3000 patients. There were methodological problems with the studies selected: definitions of AKI varied, and follow-up ranged from 6 to 75 months. Multiple risks for consequent problems after AKI were tabulated. First, did AKI increase the probability of chronic kidney disease (CKD) and end-stage renal disease (ESRD) (CKD5)? The risk of both CKD and ESRD increased in a graded manner, that is, it was higher for severe AKI versus mild or moderate. Mortality consequent to AKI was harder to predict. There was substantial heterogeneity among studies in the analysis. However, all levels of AKI may be associated with an increased occurrence of heart failure and cardiovascular disease.

There has been precedent for later untoward events in survivors of AKI in preceding studies as well. Three thousand seven hundred and sixty-nine patients with AKI were compared with 13,598 matched controls.2 The incidence rate of chronic dialysis was 2.63 in AKI survivors who needed acute dialysis during AKI versus 0.91 per 100 person-years in the control group. In another study that summarized 48 trials, totaling 47,017 enrollees, an increased risk of death was discovered (8.9 versus 4.3 deaths/100 person-years for AKI and non-AKI patients, respectively).3

QUESTION NO. 2: OUTCOMES AFTER ACUTE KIDNEY INJURY

On to the second question: recovery of renal function post-AKI has been reviewed in the elderly (65 years of age or older) and compared with younger individuals.4 An earlier review suggested that only 5% of survivors from AKI (those with severe acute tubular necrosis) require additional dialysis after discharge.5 That percentage may be an underestimate. Thirty-one percent of elderly patients who survived AKI did not recover renal function, compared with 26% of younger persons. Both numbers exceed the 5% figure.

NO FINAL ANSWERS

Although the questions are important, the answers are not final. There is a distinct possibility that other unmeasured variables or design flaws (such as ascertainment bias; that is, sicker patients are afforded more follow-up attention) are not capturing the entire story.6 This area is important, and more work should be done. Standardized definitions of AKI are needed, as are controlled trials. For now, AKI seems to be more “chronic” and dangerous than realized.