First Test to Assess Kidney Status in Longstanding Diabetes
The initial test to assess kidney status in a patient with longstanding diabetes is the urinary albumin-to-creatinine ratio (UACR) measured on a random spot urine sample, combined with estimated glomerular filtration rate (eGFR) calculated from serum creatinine. Both tests should be performed simultaneously, as they provide independent and complementary information about kidney damage and function 1.
Why Both Tests Are Essential
UACR and eGFR must be measured together because chronic kidney disease in diabetes can present with either albuminuria, reduced eGFR, or both. 1
UACR detects early kidney damage before significant loss of filtration capacity occurs, identifying patients at the microalbuminuria stage (30-299 mg/g) when interventions are most effective 1.
eGFR identifies reduced kidney function and is essential because 20-40% of diabetic patients develop reduced eGFR without significant albuminuria—a pattern increasingly recognized in both type 1 and type 2 diabetes 1, 2.
Relying on UACR alone misses a substantial proportion of diabetic kidney disease cases, particularly in type 2 diabetes where the disease evolution is more heterogeneous than in type 1 diabetes 2.
Optimal Specimen Collection
A random spot urine sample for UACR is the preferred method because it is convenient, has excellent correlation with 24-hour urine collections, and improves patient compliance 1, 3.
First morning void specimens are ideal when feasible, as they minimize the effects of postural proteinuria and provide the most reproducible results 1, 4.
Avoid measuring albumin concentration alone without creatinine, as this is susceptible to false results due to variations in urine concentration from hydration status 1, 3.
Do not use standard urine dipsticks for albumin screening, as they lack sensitivity for detecting microalbuminuria; immunoassay-based UACR testing in an accredited laboratory is required 1, 5.
Confirming Abnormal Results
Two of three specimens collected within a 3-6 month period should be abnormal before diagnosing persistent albuminuria due to high biological variability (>20%) in urinary albumin excretion 1.
However, recent evidence suggests that a single abnormal UACR between 2-20 mg/mmol (approximately 18-180 mg/g) has a positive predictive value of 96.8% for persistent microalbuminuria in type 2 diabetes, raising questions about whether repeat testing is always necessary 6.
Transient elevations in UACR can occur with exercise within 24 hours, infection, fever, congestive heart failure, marked hyperglycemia, menstruation, and marked hypertension 1.
When the first UACR is abnormal, the probability of the second test being abnormal increases with higher initial values 6.
Timing of Screening
For type 1 diabetes: Begin annual screening 5 years after diagnosis, as diabetic kidney disease typically develops after 10 years duration 1, 3.
For type 2 diabetes: Screen immediately at diagnosis and annually thereafter, because kidney disease may already be present at the time of diabetes diagnosis 1, 3.
- Up to one-third of newly diagnosed type 2 diabetes patients already have chronic kidney disease, with 6.5% having urinary albumin >50 mg/L and 28% having hypertension at diagnosis 7, 2.
Interpreting Results
Normal UACR is defined as <30 mg/g creatinine 1.
Microalbuminuria (moderately increased albuminuria) is 30-299 mg/g 1.
Macroalbuminuria (severely increased albuminuria) is ≥300 mg/g 1.
eGFR should be calculated using the CKD-EPI equation, which is preferred over older formulas and routinely reported by laboratories 1, 7, 3.
An eGFR persistently <60 mL/min/1.73 m² indicates chronic kidney disease when present for at least 3 months, regardless of albuminuria status 1.
Common Pitfalls to Avoid
Never rely on serum creatinine alone without calculating eGFR, as creatinine levels can remain normal until significant kidney function is lost 7, 3.
Do not skip albuminuria testing even when eGFR is normal, as early diabetic kidney disease presents with albuminuria before eGFR decline 7, 3.
Avoid using qualitative dipstick tests for albumin screening, as they have poor sensitivity (53.5%) compared to quantitative UACR measurement (84.9% sensitivity) 5.