Urine Specimen Collection from Nephrostomy Tubes
For patients with a pre-existing nephrostomy tube, obtain the urine specimen by aspirating directly from the nephrostomy catheter using sterile technique—never collect from the drainage bag, as this produces unreliable results with high contamination rates and false-negative results in 50-64% of cases. 1, 2
Collection Technique for Nephrostomy Tubes
The proper method involves:
- Aspirate urine directly from the nephrostomy tube itself using a sterile syringe and needle after cleaning the sampling port with 70-90% alcohol 1, 2
- Wear clean gloves whenever manipulating the urinary device to prevent contamination 1
- Collect the specimen in a sterile container for culture and sensitivity testing 2
- Transport the specimen to the laboratory within 1 hour, or refrigerate at 4°C if transport will be delayed 1, 2
Why Not the Drainage Bag
The drainage bag must be avoided because:
- Bacterial multiplication to high levels occurs while urine sits in the bag, leading to misdiagnosis of infection 1, 2
- False-negative results occur in 50-64% of biofilm-positive microorganisms when collecting from drainage bags 2
- Substantial contamination is introduced, making culture results unreliable 2
Suprapubic Aspiration Is Not Applicable Here
Suprapubic aspiration is not relevant for patients with existing nephrostomy tubes, as it is a separate procedure used for:
- Febrile infants requiring immediate antimicrobial therapy (sensitivity 95%, specificity 99%) 2
- Patients without catheters when the most sterile specimen is needed (contamination rate of only 1%) 2
A patient with a functioning nephrostomy tube already has direct access to the urinary system, making suprapubic aspiration unnecessary and potentially harmful.
Clinical Context for Nephrostomy Patients
When evaluating suspected urinary tract infection in nephrostomy patients:
- Asymptomatic bacteriuria is common and should not be treated in well-appearing patients 3
- In the presence of infectious symptoms (fever, sepsis), treat similarly to complicated pyelonephritis 3
- Obtain urinalysis, Gram stain, and quantitative culture with antimicrobial susceptibility testing if urosepsis is suspected 1
- Consider that infections are often polymicrobial in catheterized patients 1
Common Pitfalls to Avoid
- Never collect from the drainage bag—this is the most critical error, producing unreliable diagnostic results 1, 2
- Do not delay specimen processing beyond 1 hour at room temperature, as bacterial counts change rapidly 1, 2
- Do not treat asymptomatic bacteriuria in stable patients, as this leads to antibiotic resistance without clinical benefit 1, 3
- Ensure the specimen is processed promptly or refrigerated, as urine composition changes rapidly after collection 2, 4