Is the fluid coming out of a nephrostomy (nephro- meaning kidney, -stomy meaning artificial opening) tube urine?

Is the Fluid Coming Out of a Nephrostomy Tube Urine?

Yes, the fluid coming out of a nephrostomy tube is urine, as the nephrostomy tube is specifically designed to drain urine directly from the kidney's collecting system.

Understanding Nephrostomy Tubes and Their Function

A nephrostomy tube is a catheter that creates an artificial pathway (stoma) from the skin directly to the kidney's collecting system. This tube serves several critical purposes:

• Provides urinary drainage when there is obstruction in the urinary tract
• Diverts urine in cases of ureteral injury or leakage
• Allows access for diagnostic procedures
• Facilitates therapeutic interventions such as stone removal

Composition of Nephrostomy Tube Drainage

The fluid draining from a properly positioned nephrostomy tube is urine produced by the kidney. This can be confirmed by:

• Visual appearance: typically clear to yellow fluid
• Chemical analysis: contains creatinine and urea nitrogen at levels significantly higher than serum levels 1
• Diagnostic confirmation: drain fluid creatinine-to-serum creatinine ratio (DCSCR) can be measured, with a drain creatinine level just 18% higher than serum creatinine potentially signifying a urine leak 1

Clinical Confirmation Methods

If there's uncertainty about whether the fluid is urine:

1. Chemical analysis: Measure creatinine and urea nitrogen levels in the fluid

   • Urine will have significantly higher levels than blood 1
   • If levels are similar to blood, it's unlikely to be urine 1

2. Imaging confirmation:

   • CT urography with nephrographic and excretory phases is the gold standard for confirming proper tube placement and drainage 1
   • Ultrasound can identify hydronephrosis or fluid collections but has lower diagnostic accuracy 1

Common Clinical Scenarios

Properly Functioning Nephrostomy

When a nephrostomy tube is properly positioned in the kidney's collecting system:

• Clear to yellow urine should drain from the tube
• Output should correlate with expected urine production
• Drainage should improve symptoms of obstruction if present

Complications That May Affect Drainage

1. Tube dislodgement:

   • May result in drainage of non-urine fluid (blood, peritoneal fluid)
   • Requires immediate evaluation and possible reinsertion 2
   • Timing of dislodgement is crucial for management decisions 2

2. Infection:

   • May cause cloudy, malodorous drainage
   • Bacteriuria commonly develops in patients with nephrostomy tubes 3
   • Studies show bacteriuria develops in virtually all nephrostomy systems over time 3

3. Obstruction:

   • May result in decreased or absent drainage
   • Common complication requiring tube exchange or irrigation 4

Management Considerations

If there's uncertainty about whether the fluid is urine:

1. Collect a sample for creatinine and urea nitrogen measurement
2. Compare to serum levels (significantly higher values confirm urine)
3. Perform imaging to confirm proper tube position
4. Evaluate for complications if drainage appears abnormal

Conclusion

The fluid coming from a properly positioned nephrostomy tube is urine, as these tubes are specifically placed to drain urine directly from the kidney. Chemical analysis can confirm this by demonstrating elevated creatinine and urea nitrogen levels compared to serum. If there's uncertainty, imaging studies can confirm proper tube placement and function.