Will a urinalysis with LabCorp (Laboratory Corporation of America) detect proteinuria, indicating an elevated urine albumin to creatinine ratio (UACR)?

Standard Urinalysis Will Not Reliably Detect Elevated Urine Albumin to Creatinine Ratio

A standard urinalysis from LabCorp will not reliably detect an elevated urine albumin to creatinine ratio (UACR), as standard dipstick methods for protein detection lack sensitivity for detecting microalbuminuria and can miss clinically significant albuminuria. 1

Limitations of Standard Urinalysis for Detecting Albuminuria

• Standard urinalysis dipsticks for total protein are not sensitive when urine albumin concentration is in the range of 20-50 mg/L, which means they can miss clinically significant albuminuria 1
• Chemical strip methods for total protein cannot be recommended for detecting albuminuria unless they specifically measure albumin at low concentrations and express results as an albumin-to-creatinine ratio 1
• Standard protein dipsticks have poor specificity (62%) for detecting clinical proteinuria compared to ACR measurements 2

Preferred Methods for Detecting Albuminuria

The KDIGO guidelines recommend the following measurements for initial testing of albuminuria (in descending order of preference):

1. Urine albumin-to-creatinine ratio (ACR) 1
2. Reagent strip urinalysis specifically for albumin and ACR with automated reading 1

If measuring urine protein instead:

1. Urine protein-to-creatinine ratio (PCR) 1
2. Reagent strip urinalysis for total protein with automated reading 1
3. Reagent strip urinalysis for total protein with manual reading 1

Confirmation Requirements

• Positive results from reagent strip testing for albuminuria or proteinuria must be confirmed by quantitative laboratory measurement 1
• Results should be expressed as a ratio to urine creatinine wherever possible (i.e., quantify the ACR or PCR) 1
• Confirmation of ACR ≥30 mg/g (≥3 mg/mmol) on a random untimed urine should be done with a subsequent first morning void urine sample 1

Factors Affecting Urinalysis Accuracy

Several factors can lead to false-positive or false-negative results when using standard urinalysis to detect proteinuria:

• Presence of blood in urine (hematuria) can increase albumin and protein in the urine, leading to false-positive results 1
• High specific gravity (≥1.020) significantly increases the likelihood of false-positive proteinuria readings 3
• Other confounding factors include ≥3+ leukocyte esterase, ketonuria, ≥1+ urobilinogen, ≥2+ bilirubin, ≥2+ bacteria, ≥3 RBC/hpf, ≥10 WBC/hpf, and/or ≥6 epithelial cells/hpf 3
• Exercise can temporarily increase albumin and protein in the urine 1
• Urinary tract infections can cause increased protein in the urine 1

Recommendations for Clinical Practice

• For accurate detection of an elevated UACR, specifically request a urine albumin-to-creatinine ratio test rather than relying on standard urinalysis 1
• The most reliable method is the immunoturbidimetric laboratory assay, which has >95% sensitivity and specificity for detecting moderately increased albuminuria 1
• If standard urinalysis is the only available initial test, be aware that a negative result for protein does not rule out the presence of clinically significant albuminuria 1
• Adults at increased risk for chronic kidney disease with a negative result for protein on a standard dipstick test, especially those with diabetes, should undergo testing with either an albumin-specific dipstick or an untimed urine measurement for the albumin-creatinine ratio 1

Clinical Implications

• Total proteinuria and albuminuria perform equally as predictors of renal outcomes and mortality in patients with CKD 4
• Both ACR and PCR are effective at predicting outcomes and are more convenient than 24-hour urine samples 4
• When confounding factors are present in urinalysis (such as high specific gravity or hematuria), confirmatory ACR testing should be performed according to clinical algorithms for CKD management 3

In summary, a standard urinalysis from LabCorp is not a reliable method for detecting an elevated urine albumin to creatinine ratio, particularly in the range that would indicate early kidney disease. Specific testing for urine albumin with calculation of the albumin-to-creatinine ratio is necessary for accurate assessment.