AKI vs CKD vs Acute-on-Chronic
An abnormal creatinine tells you kidney function is abnormal. The timeline tells you whether it is acute, chronic, or both.
Find the baseline
Prior creatinine and eGFR values are often the highest-yield first step. A single abnormal creatinine cannot reliably distinguish AKI from CKD.
Chronicity classifies CKD
Persistent kidney abnormalities for more than 3 months support CKD. One low eGFR during an acute illness does not establish chronic disease.
CKD does not explain a new rise
A patient with established CKD can still develop superimposed AKI. An abrupt creatinine increase above a stable chronic baseline requires a new explanation.
Ask what changed
Poor intake, GI losses, hypotension, infection, surgery, urinary retention, nephrotoxins, and medication changes can identify an acute trigger. Urinalysis, sediment, volume/perfusion assessment, obstruction evaluation, and imaging are selected based on the story.
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