Can a Urinary Tract Infection (UTI) cause falsely elevated glucose, protein, and ketones in urinalysis results?

Can a UTI Cause False Positive Glucose, Protein, and Ketones on Urinalysis?

Yes, a urinary tract infection (UTI) can cause falsely elevated protein in urinalysis, but it does not typically cause false positive glucose or ketones. The presence of infection in the urinary tract can affect urinalysis results in several specific ways.

Effect of UTI on Urinalysis Parameters

Protein

• UTIs can cause falsely elevated protein levels in urinalysis due to the presence of inflammatory proteins and bacterial proteins in the urine 1
• According to the 2024 KDIGO guidelines, infection increases albumin and protein in the urine, which can lead to falsely elevated albumin-to-creatinine ratio (ACR) or protein-to-creatinine ratio (PCR) 1
• Symptomatic urinary infection can cause production of protein from the organism itself, further contributing to proteinuria 1

Glucose

• UTIs do not typically cause false positive glucose readings in urinalysis 1
• Glycosuria is primarily associated with diabetes mellitus, and urine glucose testing has been largely supplanted by self-monitoring of blood glucose 1
• If glucose is detected in urine, it generally reflects true hyperglycemia rather than being a false positive from infection 1

Ketones

• UTIs do not typically cause false positive ketone readings in urinalysis 1
• False positive ketone readings are more commonly associated with certain medications (like sulfhydryl drugs including captopril) rather than infection 1
• False negative ketone readings can occur when test strips have been exposed to air for an extended period or when urine specimens are highly acidic 1

Factors Affecting Urinalysis Interpretation in UTI

Collection Method and Contamination

• Improper collection technique can affect urinalysis results regardless of UTI status 2
• A study found that even in disease-free women, urinalysis often shows abnormal results with both "non-clean" and "ideal" collection techniques 2
• Leukocyte esterase, white blood cells, and bacteria are commonly elevated in UTIs but can also be present due to contamination 2

Other Confounding Factors

• The presence of ≥3+ blood, ≥3+ leukocyte esterase, high specific gravity (≥1.020), and other abnormalities can affect the reliability of urinalysis for detecting proteinuria 3
• High specific gravity and hematuria (both common in UTIs) are strong predictors of false positive protein results 3

Clinical Implications

Diagnostic Considerations

• When interpreting urinalysis results in suspected UTI, consider that:
  • Nitrite is the most specific indicator of UTI with low false positive rates 2
  • Leukocyte esterase, while sensitive, can be positive in the absence of infection 1
  • Protein may be elevated due to the infection itself rather than indicating kidney disease 1

Confirmation Testing

• If abnormal glucose, protein, or ketones are found in a patient with UTI:
  • Glucose: Consider confirming with blood glucose testing to rule out diabetes 1
  • Protein: Repeat testing after resolution of the UTI or consider albumin-to-creatinine ratio testing 1, 3
  • Ketones: If concerned about diabetic ketoacidosis, blood ketone testing is more reliable than urine ketone testing 4

Conclusion

While UTIs can cause falsely elevated protein in urinalysis due to inflammation and bacterial proteins, they do not typically cause false positive glucose or ketones. When interpreting urinalysis results in patients with UTI, it's important to consider the potential impact of the infection on various parameters and confirm abnormal findings with appropriate follow-up testing after resolution of the infection.