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Pinson and Tang CDI Pocket Guide
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Acute Kidney Injury (AKI): Creatinine Baseline Explained

July 30, 2019

AKI Diagnostic Criteria: 1.5x Baseline

A CDI Pocket Guide customer recently sent us a question regarding the 1.5x diagnostic criteria for acute kidney injury, and we thought others may benefit:

The CDI Pocket Guide on page 62 includes one of the AKI diagnostic criteria as: "Increase in Creatinine > 1.5x baseline (historical or measured) which is known or presumed to have occurred within the prior 7 days.”

However, on page 63 the Guidelines for applying this AKI criterion states: The 1.5x diagnostic criteria “can be applied prospectively and retrospectively with broad interpretation of the baseline level which may be one from 6 months or even one year previously if there is no known CKD.”

How we can have a baseline up to one year old but the diagnostic criteria states within the prior 7 days?

Known vs. "Presumed" Baseline

A creatinine level from 6 months to as much as a year before may be used as a baseline to identify AKI at the time of admissionif the patient did not have preexisting CKD or another dramatic change in health since then.  If a patient is admitted for an acute illness and the creatinine is > 1.5x the past baseline level, it is “presumed” to have occurred within the prior 7 days, and AKI can be diagnosed.

For example, a previously healthy patient is admitted for nausea, vomiting, diarrhea and dehydration. His creatinine level was 2.0, and his creatinine level four months ago was 1.0. It is presumed that the creatinine increased to twice the previous level during this acute illness (within 7 days) confirming AKI.

In such circumstances the elevated admission creatinine would also be expected to return to or near the historical baseline further confirming it as acute. For example, if the prior baseline were 1.0 and the admission creatinine of 2.0 returned to 1.2 at discharge, the diagnosis of AKI is indisputable.

Should the elevated admission creatinine unexpectedly remain well above the prior baseline, AKI is not fully substantiated.  Further investigation is necessary to determine the cause. For example, an admission creatinine of 2.0 (with a prior baseline of 1.0) that remains elevated between 1.7−2.0 does not confirm AKI.

How to apply to CKD

Patients with CKD may also have AKI if the patient is admitted with a creatinine level that is 1.5x their baseline. For example, a patient with CKD and a stated baseline of 1.8 is admitted with a creatinine of 2.5 which decreases to 1.6 with IV fluids. The true baseline is now 1.6 and 2.5 is > 1.5x this level, confirming AKI with chronic CKD.

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