Differentials
Chronic kidney disease
SIGNS / SYMPTOMS
Reduced kidney function with elevation of creatinine is chronic (>3 months), although there may be acute on chronic kidney disease.
INVESTIGATIONS
An acutely elevated serum creatinine is diagnostic of AKI and indicative of reduced clearance. The clinical context is important in differentiating AKI from a progression of CKD at initial presentation if there are no recent comparison creatinine values available for the patient. Features that favour a diagnosis of CKD (although do not exclude AKI) include hypocalcaemia, hyperphosphataemia, anaemia, and small kidneys (sometimes scarred) on ultrasound.[10][75]
There are no causes of chronically elevated serum creatinine other than reduced glomerular filtration (except for minor elevations in subjects with increased muscle mass and from certain medications).
Creatinine elevation over time provides a chronological perspective and assists in differentiating acute from chronic kidney disease.
Twenty-four-hour urine study for creatinine clearance demonstrates the level of kidney function; the use of 131-I iothalamate is the definitive test for this purpose.
Increased muscle mass
SIGNS / SYMPTOMS
Any elevation of creatinine is minor and typically non-acute.
INVESTIGATIONS
Acutely elevated serum creatinine is diagnostic of AKI.
Minor elevations in creatinine from increased muscle mass may rarely be seen.
Twenty-four-hour urine study for creatinine clearance demonstrates normal kidney function.
Drug side effect
SIGNS / SYMPTOMS
Certain medicines such as cimetidine or trimethoprim may lead to an elevation of creatinine that is minor and non-acute (most commonly in patients with pre-existing CKD).
INVESTIGATIONS
Discontinuing the medicine should result in normalising of the serum creatinine.
Twenty-four-hour urine study for creatinine clearance should demonstrate normal function.
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