Urine from indwelling catheters

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.

Urine from iteat conduits

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.

Urine transport

• 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

A. Physical examination of urine

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

Technique

Advantages

Disadvantages

Clean voided bag samples

Clean perineum and external genitalia. Apply bag. Remove promptly and perform urinalysis after micturition

Non-invasive

Contamination—high false positive (63%) Positive culture may not be sufficient to commence antibiotic therapy

Suprapubic aspiration

Insert a 1.5-inch, 22-gauge needle, 1-2 cm above symphysis pubis under ultrasound guidance; aspirate 5 mL of urine

Safe

High sensitivity (>95%)

Quick

Hematuria, intestinal or viscus perforation (risk very small)

Success rate variable— 46-96%

Can only be used in children <2 years age

Urethral catheterization

Insert a 5 or 6 F urethral catheter into bladder using lidocaine lubricant jelly; discard first few drops of urine

Safe

Successful in virtually 100% of cases

Invasive

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

Gold standard

Correlates reasonably well with suprapubic aspiration

TABLE 1.2. Factors affecting urine color

Color

Causes

Yellow Orange

Blue or green Brown

Hematuria

Hemoglobinuria

Myoglobinuria

Beet-root

Blackberries

Rifampicin

Heavy metal poisoning (mercury, lead)

Riboflavin

Phenacetin

Concentrated urine (dehydration)

Phenazopyridine

Sulfasalazine

Biliverdin

Dyes (methylene blue, indigo carmine)

Cimetidine

Promethazine

Hemorrhage

Urobilinogen

Porphyria

Rhubarb

Aloe

Anti-malarials (e.g., chloroquine)

Antibiotics (e.g., nitrofurantoin, metronidazole)

Methyldopa

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

Table 1.3.

Reference range for urine dipstick parameters

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