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Interpreting Laboratory Data

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WBC

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Laboratory Interpretations for Urinary

Tract Infections/ UrinalysisUrine Content

Urine is a healthy person is sterile (bacteria free)

Urine in healthy people contains:

• a pH of

•

a specific gravity (density) of• a yellow color

• Minerals such as Na, Ca, Sulfates, K, water (95%), HCO3…ect

Urine in healthy people should not contain:

• Bacteria

•Odor

• Turbidity

• Nitrites

• Proteins, cats, RBC, and WBC

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Urine Analysis

In regards to urinary tract infections, the following asimportant indicators on a urine analysis:

• Presence of WBC

• Abnormal specific gravity (usually higher than normal)• Abnormal pH (usually a higher pH than normal)

• Presence of nitrites

• Presence bacteria

•

Presence of leukocyte esterase• Presence of casts in the urine

Remember a urine analysis does not necessarily help identifythe organism but helps determine if bacteria are present

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CON’T 

• Dipstick analysis for leukocyte esterase, an indirect testfor the presence of pyuria, is the least expensive andtime intensive test. It is estimated to have a sensitivityof 75-96% and specificity of 94-98%.

•When compared to culture, dipstick is less sensitive forlower thresholds for UTI (i.e., 102-104 cfu/mL) andspecificity is correspondingly higher for the samethresholds.

• Microscopic examination of unstained, centrifugedurine by a trained observer under 40x power has asensitivity from 82-97% and a specificity of 84-95%,again varying depending on defined thresholds for UTI.

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CON’T 

•  urine culture, sensitivity varies from 50 to

95%, depending on threshold for UTI, and

specificity varies from 85-99%. Urine culture is

not recommended to diagnose or verify

uncomplicated UTI because the sensitivity of

urine culture is limited and the required delay

for results.