From the Guidelines
The initial workup for proteinuria should begin with the measurement of urine albumin-to-creatinine ratio (ACR) as the first-line test, followed by urine protein-to-creatinine ratio, and then reagent strip urinalysis for total protein with automated reading, as recommended by the KDIGO 2012 CKD guideline 1.
Key Considerations
- The KDIGO guideline suggests using an early morning urine sample for initial testing of proteinuria, with a preference for urine ACR as the first-line measurement 1.
- The guideline recommends a step-wise approach to evaluating proteinuria, starting with the measurement of urine ACR, followed by other tests if necessary.
- The use of reagent strip urinalysis for total protein with automated reading is also recommended as a third-line test for detecting proteinuria 1.
Evaluation and Management
- If proteinuria is confirmed, a comprehensive evaluation should follow, including a complete medical history, physical examination, and basic laboratory tests.
- Additional tests, such as hepatitis B and C serologies, HIV testing, and serum and urine protein electrophoresis, may be necessary to evaluate for underlying causes of proteinuria.
- The workup should be tailored based on clinical presentation, with nephrotic-range proteinuria (>3.5 g/day) requiring more urgent and extensive evaluation than lower levels of proteinuria.
- Renal ultrasound and kidney biopsy may be necessary for definitive diagnosis and management of proteinuria, especially in cases with abnormal renal function or active urinary sediment.
From the Research
Proteinuria Workup
- Proteinuria is a key indicator of kidney disease and has significant prognostic value 2
- The workup for proteinuria involves various tests, including semi-quantitative and quantitative methods, each with its strengths and weaknesses 2
Test Methods
- Semi-quantitative tests are easy to handle but have limitations such as incomplete quantification, lack of specificity, and high false positive rates 2
- Quantitative methods, such as immunoassays, offer high test accuracy and targeted detection of specific protein molecules, but are more expensive and require laboratory access 2
- The protein-creatinine ratio (PCR) and albumin-creatinine ratio (ACR) are commonly used to quantify proteinuria, with PCR being more sensitive than ACR in predicting clinically relevant proteinuria 3
Interpretation of Results
- The interpretation of proteinuria test results should consider the clinical context, including the patient's age, gender, and medical history 3
- The blood urea nitrogen (BUN) to creatinine ratio can be a valuable tool in determining renal functional and structural integrity, but should be interpreted with awareness of extrarenal factors that can affect these levels 4, 5
- Elevations in BUN and/or serum creatinine levels do not necessarily indicate structural renal disease, and normal values do not rule out significant reduction in glomerular filtration rate 5