Interpretation of urinalysis from patients on long-term indwelling catheterization is problematic for a variety of reasons, and unnecessary treatment may result in the emergence of antibiotic -resistant organisms.
• Bladder colonization is inevitable and can occur within 4 days of catheter placement
• A positive bacterial growth does not necessarily suggest a significant UTI
• Antibiotic therapy is unlikely to eradicate the targeted pathogen while the patient remains catheterized
• Colonizing flora may change over time
In such patients, a urine sample should only be sent if a UTI is suspected in a systemically unwell patient. Urine must be taken from the collection port and not from the catheter bag.
Skin organism contamination is inevitable in patients with urinary diversions and therefore urostomy bag urine is not suitable. If clinically indicated, urine collection should be via a catheter introduced as far into the conduit as it will go.
Urine collection in children
• UTIs are common in children
• Urine collection can be difficult
• Toilet-trained children can provide an MSU
• Urine from children not toilet trained can be obtained by a "clean voided" bag sample, suprapubic aspiration, or transurethral catheterization
The relative merits and drawbacks are discussed in Table 1.1.
• Specimen must reach laboratory within 2 hours
• Delay can result in either over-proliferation or death of organisms
• Alternatively, store at a temperature of 4°C if a delay is encountered and analyze as soon as possible
• Beware that refrigeration can result in a decreased number of urinary leucocytes
Color: The endogenously produced pigment, urochrome, gives urine its characteristic yellow-brown color. Since urochrome is excreted at a uniform rate (i.e., the same amount per hour), the color of urine varies primarily with urine output, which in turn is predominantly affected by the patient's hydration status. In addition, a variety of other compounds related to food, medication, and infection can alter the color of urine. Patients commonly complain of altered urine color and it is important to be aware of common urine color-altering factors, as listed in Table 1.2.
Turbidity: Cloudy urine is commonly caused by—
• Phosphaturia—will typically occur after consumption of a large meal or quantity of milk in susceptible patients.
TABLE 1.1. Comparision of urine collection techniques in children
Clean voided bag samples
Clean perineum and external genitalia. Apply bag. Remove promptly and perform urinalysis after micturition
Contamination—high false positive (63%) Positive culture may not be sufficient to commence antibiotic therapy
Insert a 1.5-inch, 22-gauge needle, 1-2 cm above symphysis pubis under ultrasound guidance; aspirate 5 mL of urine
High sensitivity (>95%)
Hematuria, intestinal or viscus perforation (risk very small)
Success rate variable— 46-96%
Can only be used in children <2 years age
Insert a 5 or 6 F urethral catheter into bladder using lidocaine lubricant jelly; discard first few drops of urine
Successful in virtually 100% of cases
Urethral trauma/ hematuria
False positives (80%)
Takes longer than suprapubic aspiration
Cannot be used in older children
Clinical comments Positive results usually require validation by using an invasive technique
Correlates reasonably well with suprapubic aspiration
TABLE 1.2. Factors affecting urine color
Blue or green Brown
Heavy metal poisoning (mercury, lead)
Concentrated urine (dehydration)
Dyes (methylene blue, indigo carmine)
Anti-malarials (e.g., chloroquine)
Antibiotics (e.g., nitrofurantoin, metronidazole)
Diagnosis is completed by either acidifying the alkaline urine to dissolve the excess phosphate crystals (urine turns clear) or by visualizing the precipitated phosphate crystals under microscopy
• UTI—pungent-smelling, cloudy urine is likely to be secondary to pyuria associated with an infective process
• Rare causes of turbid urine include chyluria (lymph fluid in urine), hyperoxaluria, and lipiduria
B. Urine dipstick analysis
Dipstick testing is useful in assessing patients with—
• Renal disease
• Urological disorders
• Metabolic disease not related to the kidneys
Reference range for urine dipstick parameters
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