UACR Cannot Be Computed from Serum Creatinine Alone
You cannot calculate urinary albumin-to-creatinine ratio (UACR) from a serum creatinine value of 66.6 µmol/L—UACR requires a urine sample that measures both urine albumin and urine creatinine concentrations. 1
What UACR Actually Measures
- UACR is the ratio of urine albumin (mg) to urine creatinine (g), typically expressed as mg/g creatinine, and is obtained from a spot urine sample—not from blood 1
- The serum creatinine value you provided (66.6 µmol/L, approximately 0.75 mg/dL) is used to calculate estimated glomerular filtration rate (eGFR) using the CKD-EPI equation, which assesses overall kidney function but does not provide information about albuminuria 1
How to Obtain UACR
- Collect a random spot urine sample, preferably first morning void, which has the lowest coefficient of variation (31%) and provides the most reliable results 2, 3
- The laboratory will measure both urine albumin concentration (mg/L) and urine creatinine concentration (mg/dL or g/L) from the same sample 1
- UACR is calculated as: (urine albumin in mg/L) ÷ (urine creatinine in g/L), with results reported as mg/g creatinine 1, 2
Clinical Context for This Patient
- For a 50-year-old male with serum creatinine of 66.6 µmol/L (0.75 mg/dL), the eGFR would be approximately 100-110 mL/min/1.73 m², indicating normal kidney filtration function 1
- However, normal eGFR does not exclude early kidney damage—albuminuria can be present even when eGFR is preserved, representing early glomerular injury 1
- UACR screening is recommended annually for adults with diabetes (starting at diagnosis for type 2, or 5 years after diagnosis for type 1) or those with hypertension and other kidney disease risk factors 1, 2
Interpretation Framework Once UACR Is Obtained
- Normal: UACR <30 mg/g creatinine 1, 3
- Moderately increased albuminuria (A2): UACR 30-299 mg/g creatinine 1, 2
- Severely increased albuminuria (A3): UACR ≥300 mg/g creatinine 1, 2
- Confirm any elevated result with 2 out of 3 specimens over 3-6 months due to high biological variability (>20% between measurements) 1, 2, 4
Common Pitfalls to Avoid
- Do not confuse serum creatinine with urine creatinine—they measure different things and cannot be used interchangeably 1
- Exclude transient causes before confirming chronic albuminuria: exercise within 24 hours, urinary tract infection, fever, congestive heart failure, marked hyperglycemia, menstruation, or uncontrolled hypertension can falsely elevate UACR 1, 2, 5
- Measuring urine albumin alone without creatinine is susceptible to false results due to variations in urine concentration from hydration status 1