Clinical use
Diagnosis of CAPD peritonitis.
Background
Continuous ambulatory peritoneal dialysis (CAPD) is used as an alternative to haemodialysis for the management of patients with end-stage renal failure. In this procedure, the patient’s own peritoneal membrane is used to dialyse waste products from the patient’s blood. This involves the use of a closed system of tubing, sterile dialysate fluid in a bag, and a catheter that directs the fluid in and out of the peritoneal cavity.
Peritonitis is a significant complication of CAPD. Infections can arise from direct contamination of the catheter, or, on rare occasions, originating from an intra-abdominal focus. The vast majority of CAPD infections are uni-microbial. Diagnosis is usually made on the presence of two or more of the following criteria: cloudy dialysate effluent, symptoms of peritonitis, and/or positive microbiology.
Microscopy and Culture
Turbidity of the effluent generally represents a raised white blood cell (WBC) count. Other cellular materials, including fibrin, blood, or chyle can cause turbidity. Microscopy is essential to confirm the presence of WBC. The presence of >100 WBCx106/L correlates closely with infection.
Recovery of organisms by culture can be challenging. Direct inoculation of blood culture bottles by renal teams can be useful for early detection. Blood culture bottles must be accompanied by a separate specimen for microscopy and direct culture.
Reference ranges
The presence of >100 WBC x 106 per litre in CAPD fluid correlates closely with infection.
Patient preparation
- Collect specimens before commencing antimicrobial therapy where possible
- Use strict aseptic technique
Specimen requirements
- If possible, a whole dialysate fluid bag for sampling under controlled laboratory conditions may be performed. This should be transported to the laboratory in transported in rigid, leakproof outer container.
- Where safe transport and receipt of the whole bag is considered impractical a sample of fluid can be taken. Withdraw fluid aseptically from the injection port of the plastic dialysate bag with a sterile needle and syringe. Transfer to an appropriate CE-marked leakproof container and transport in a sealed plastic bag.
- Blood culture bottles should be inoculated with fluid. 5-10mL of dialysate fluid from the port of the bag should be inoculated aseptically into both the aerobic bottle (green top) and the anaerobic bottle (orange top). This must be accompanied by a separate bottle for direct culture and microscopy.
Minimum volume
A volume of 10-50mL of fluid is considered suitable.
A number of specimens and frequency of specimen collection are dependent on the clinical condition of the patient.
Limitations & restrictions
Specimens should be transported and processed as soon as possible. If processing is delayed, refrigeration is preferable to storage at ambient temperature.
Do not send CAPD samples via the pneumatic tube as there is a risk of the sample leaking and it may also affect the cell count of the sample.
Turnaround time
- Microscopy: 2 hours
- Culture: up to 7 days
Analysing laboratory
Microbiology Lab, James Cook University Hospital, Marton Road, TS4 3BW