Is a urinalysis report showing nitrite, positive leukocyte esterase, many bacteria, and significant white blood cells (WBCs) per high power field (hpf) consistent with a urinary tract infection (UTI) and what does the presence of renal tubular epithelial (RTE) cells indicate?

Urinalysis Report Analysis for Urinary Tract Infection

The urinalysis report is highly consistent with a urinary tract infection (UTI), but the presence of renal tubular epithelial (RTE) cells is concerning and suggests possible renal involvement beyond a simple UTI.

Analysis of UTI Indicators

Chemical Findings Supporting UTI:

• Positive nitrite: Indicates the presence of bacteria that reduce nitrates to nitrites, with specificity of 93-98% for UTI 1
• Leukocyte esterase 2+: Strong indicator of pyuria, with sensitivity of 83% for UTI 1
• pH 7.0: Slightly alkaline urine can be consistent with certain bacterial infections
• Protein 1+: May indicate inflammation in the urinary tract

Microscopic Findings Supporting UTI:

• 80-100 WBCs/hpf: Significant pyuria (>10 WBCs/hpf is considered diagnostic for UTI) 1
• Many bacteria: Direct visualization of bacteria strongly supports infection
• 5-10 RBCs/hpf: Microscopic hematuria often accompanies UTI

Concerning Finding: Renal Tubular Epithelial Cells

The presence of 10-15 RTE cells/hpf is the microscopic result that would concern a urinalysis supervisor, as it is inconsistent with a simple UTI. RTE cells in significant numbers suggest:

1. Possible renal parenchymal involvement (pyelonephritis)
2. Renal tubular damage or injury
3. Possible nephrotoxicity

This finding elevates the concern beyond uncomplicated UTI to possible upper urinary tract involvement or renal pathology.

Potential Source of Error

The most probable cause of error in the report would be confusion between RTE cells and transitional epithelial cells or leukocytes:

• RTE cells can be mistaken for:
  • White blood cells (particularly when WBCs are swollen)
  • Transitional epithelial cells from the lower urinary tract
  • Squamous epithelial cells (though these are typically larger)

RTE cells have distinct characteristics including:

• Slightly larger than WBCs (1.5-3× the size)
• Cuboidal or columnar shape
• Round to oval nuclei
• Granular cytoplasm

Clinical Implications

The combination of positive nitrite, leukocyte esterase, pyuria, and visible bacteria provides high diagnostic accuracy for UTI. The sensitivity of combined leukocyte esterase and nitrite tests is 93% with specificity of 72% 1.

However, the presence of RTE cells suggests this may not be a simple UTI and warrants:

• Consideration of pyelonephritis
• Evaluation of renal function
• Possible imaging of the upper urinary tract
• More aggressive treatment approach than for uncomplicated UTI

Common Pitfalls in Urinalysis Interpretation

1. Contamination can lead to false-positive results, though this is less likely with a catheterized specimen 2
2. Improper specimen handling can affect results if not processed within 1-4 hours 1
3. Relying solely on dipstick without microscopic examination can miss important findings like RTE cells
4. Failing to recognize that the presence of RTE cells elevates the clinical concern beyond simple cystitis

In summary, while this urinalysis strongly supports a diagnosis of UTI, the presence of RTE cells suggests possible renal involvement that requires additional evaluation and potentially more aggressive management.