From the Guidelines
For a patient with a protein-to-creatinine ratio of 6g, I strongly recommend ordering a urine ACR as the initial test for proteinuria, as suggested by the KDIGO 2012 CKD guideline 1. This is because the KDIGO guideline suggests using urine ACR as the first-line measurement for initial testing of proteinuria, followed by urine protein-to-creatinine ratio, and then reagent strip urinalysis for total protein with automated reading.
- The urine ACR is preferred due to its high sensitivity and specificity in detecting proteinuria.
- Additionally, a comprehensive panel of laboratory tests should be ordered to evaluate the underlying cause and assess end-organ damage, including:
- Complete urinalysis with microscopic examination
- 24-hour urine protein collection to confirm the degree of proteinuria
- Serum creatinine, blood urea nitrogen (BUN), estimated glomerular filtration rate (eGFR)
- Complete blood count (CBC), comprehensive metabolic panel, lipid profile, serum albumin, and total protein
- Serological tests such as antinuclear antibody (ANA), anti-double stranded DNA antibody, complement levels (C3, C4), serum and urine protein electrophoresis, hepatitis B and C serologies, and HIV testing
- A renal ultrasound would also be valuable to assess kidney size and structure, as severe proteinuria can be associated with glomerular diseases like nephrotic syndrome, diabetic nephropathy, or lupus nephritis 1.
- The choice of tests is guided by the need to determine the specific cause of proteinuria, assess kidney function, identify complications, and guide appropriate treatment decisions.
From the Research
Laboratory Tests for Protein-to-Creatinine Ratio of 6g
To assess a protein-to-creatinine ratio of 6g, the following laboratory tests may be considered:
- Urine protein electrophoresis and immunofixation (uPEI) to examine the urinary protein electrophoretic pattern and determine the type of proteinuria 2
- Total protein and albumin to creatinine ratio (uPCR and uACR) to assess the proportion of higher molecular weight protein in urine total protein content 2
- Albumin to total protein ratio (uAPR) to predict the type of proteinuria and diagnose primary tubulointerstitial disorders on renal biopsy 2
- Measurement of tubular proteins (N-acetyl-β-D-glucosaminidase, NAG, and β2-microglobulin) and expression of these as ratios to creatinine (uNCR and uβ2CR) to predict a tubular pattern of urinary protein 2
- Urine albumin-specific dipstick, immunochemical techniques, and size-exclusion high-performance liquid chromatography to assess urinary albumin 3
Rationale for Laboratory Tests
The rationale for using these laboratory tests is to assess the type and amount of proteinuria, which is a strong predictor of adverse cardiovascular and kidney events 3, 4, 5. The protein-to-creatinine ratio is a simple and convenient method for assessing proteinuria in clinical practice 6.
Interpretation of Laboratory Results
The results of these laboratory tests can be used to stratify risk in patients with chronic kidney disease (CKD) and predict patient outcomes, including all-cause mortality, start of renal replacement therapy (RRT), and doubling of serum creatinine level 4, 5. A protein-to-creatinine ratio of 6g indicates significant proteinuria, which is associated with a substantially increased risk of RRT and death 4.