What causes sediment in a Foley (Foley catheter)?

Causes of Sediment in Foley Catheters

The primary causes of sediment in Foley catheters are crystalline biofilm formation due to urease-producing bacteria (particularly Proteus mirabilis), mineral precipitation, and catheter-associated urinary tract infections.

Bacterial Biofilm Formation

Bacterial colonization is the most significant contributor to sediment formation in Foley catheters:

• Urease-producing bacteria: Particularly Proteus mirabilis, which can:

  • Colonize the catheter forming extensive biofilms 1
  • Generate ammonia from urea, elevating urine pH
  • Create an alkaline environment that promotes crystal formation 2

• Other common pathogens that contribute to biofilm formation:

  • Coagulase-negative staphylococci
  • Staphylococcus aureus
  • Enterococcus species
  • Pseudomonas aeruginosa
  • Candida species 3

Crystalline Deposits

When bacteria colonize catheters, they create conditions that lead to crystal formation:

• Mineral precipitation: As urine pH rises (especially above 7.0), calcium and magnesium phosphates precipitate in the urine and adhere to the catheter biofilm 1

• Crystal types:

  • Calcium phosphate (hydroxyapatite)
  • Magnesium ammonium phosphate (struvite)
  • Calcium oxalate (less common)

• Progressive encrustation: The continued development of crystalline biofilm eventually blocks urine flow through the catheter 1

Contributing Factors

Several factors increase the risk of sediment formation:

• Catheter material: Some catheter materials have surface irregularities that enhance microbial adherence 3

• Duration of catheterization: Longer indwelling times increase biofilm formation risk

• Urinary stasis: Poor drainage allows bacteria to multiply and form biofilms

• Dehydration: Concentrated urine promotes crystal formation

• Urinary tract infection: Existing infections accelerate biofilm development

Clinical Consequences

Sediment accumulation leads to several complications:

• Catheter blockage: Crystalline biofilm blocks urine flow, leading to:

  • Urinary leakage around the catheter
  • Painful bladder distension
  • Potential reflux to kidneys 1

• Stone formation: The process of crystal deposition can initiate bladder stone formation 1

• Persistent infection: P. mirabilis establishes stable residence in these stones and is extremely difficult to eliminate with antibiotics 1

• Serious complications: If blocked catheters are not identified and changed promptly, patients may develop:

  • Pyelonephritis
  • Septicemia
  • Endotoxic shock 1

Prevention Strategies

To minimize sediment formation:

• Maintain closed drainage systems: Use a closed catheter drainage system with ports in the distal catheter for needle aspiration of urine 4

• Proper positioning: Keep the drainage bag and connecting tube below bladder level to prevent backflow 4

• Minimize manipulation: Reduce disconnection of the catheter junction to prevent introducing bacteria 4

• Adequate hydration: Encourage fluid intake to dilute urine and reduce crystal formation

• Consider catheter materials: Silver alloy-coated urinary catheters may reduce or delay the onset of bacteriuria 4

• Avoid routine irrigation: Do not routinely irrigate catheters unless specifically indicated for hematuria or obstruction 4

Important Caveats

• All types of Foley catheters, including silver- or nitrofurazone-coated devices, are vulnerable to encrustation and sediment formation 1

• Routine replacement of catheters is not recommended; replace only when obstructed or malfunctioning 4

• Surveillance urine cultures in asymptomatic patients are not recommended 4

• Asymptomatic bacteriuria should not be treated with antibiotics in catheterized patients 4, 5