From the Guidelines
For patients suspected of having Acute Kidney Injury (AKI), the most recommended urine studies include urinalysis with microscopy, as it can reveal important diagnostic clues such as hematuria, pyuria, casts, or crystals, which can help identify the underlying cause of AKI 1. When evaluating a patient with suspected AKI, it is crucial to consider the following urine studies:
- Urinalysis with microscopy to identify cellular elements, casts, and crystals that may indicate specific causes of AKI
- Urine chemistry to assess concentrating ability and identify potential electrolyte imbalances
- Biomarkers such as urine protein-to-creatinine ratio to help identify glomerular pathology These studies should be obtained early in the evaluation process to guide further management and treatment. It is also important to note that the evaluation of AKI should include a thorough history, physical examination, and laboratory analysis of blood, in addition to urine studies 1. Monitoring patients with AKI with measurements of serum creatinine and urine output is also essential to stage the severity of the disease 1. However, urine volume measurement is less important than measurement of serum creatinine in the diagnosis of AKI 1. In specific clinical scenarios, additional tests like urine eosinophils, myoglobin, or urine immunoelectrophoresis may be warranted to guide further management. Overall, the choice of urine studies should be guided by the clinical presentation and suspected underlying cause of AKI, with the goal of identifying the cause and guiding appropriate treatment to improve patient outcomes.
From the Research
Urine Studies for AKI
Urine studies are essential for the diagnosis and management of Acute Kidney Injury (AKI). The following urine studies are recommended:
- Urine output monitoring: Oliguria is an earlier sign of impending AKI than an increase in serum creatinine 2
- Fractional excretion of sodium (FENa): A low FENa (< 1%) is present in 77.3% of patients with AKI 2
- Fractional excretion of urea (FEUrea): A low FEUrea (< 35%) is present in 63.2% of patients with AKI 2
- Urinary strong ion difference (SIDu): Decreased values of SIDu are associated with AKI development 3
- Urinary sodium (NaU) and chloride (ClU): Decreased values of NaU and ClU are associated with AKI development 3
- Urinary biochemistry: Sequential evaluation of urine biochemistry can help characterize AKI development and management 3
- Quantitative proteinuria: Measurement of quantitative proteinuria is recommended for CKD risk stratification, but is often underutilized in patients with AKI 4
Additional Tests
Other tests that may be useful in the diagnosis and management of AKI include:
- Urine microscopy: To identify the nature and site of kidney injury 5
- Blood tests: To evaluate traditional acid-base and renal parameters, such as serum creatinine and electrolytes 5, 3
- Physicochemical analysis of blood and urine: To describe sequential alterations in blood and urine in the course of AKI development 3