JAMA Diagnostic Test Interpretation
November 10, 2022
Peritoneal Fluid Analysis in Peritoneal Dialysis–Associated Peritonitis
Jeffrey Perl, Ziv Harel, Sharon J. Nessim
JAMA. Published online November 10, 2022. doi:10.1001/jama.2022.21289
A62-year-old woman undergoing peritoneal dialysis (PD) for kidney failure due to IgA nephropathy presented to the PD clinic with a 1-day history of severe abdominal pain and cloudy PD fluid. Seven days prior, she inadvertently broke aseptic technique when tightening a leaking connection of her PD catheter tubing. On presentation, she was afebrile and had normal vital signs. Physical examination revealed diffuse abdominal tenderness. Cloudy fluid that was drained from her PD catheter was sent for laboratory analysis (Table 1).
What Would You Do Next?
- Administer empirical broad-spectrum intraperitoneal antibiotics
- Administer empirical broad-spectrum intravenous antibiotics
- Await peritoneal dialysis fluid culture results before starting intraperitoneal antibiotics
- Send blood cultures
- Administer empirical broad-spectrum intraperitoneal antibiotics
PD-associated peritonitis occurs in approximately 30% to 40% of patients during their course of PD treatment1,2and develops when infectious organisms gain access to the peritoneal cavity. Infection can occur through “touch contamination,” involving a breach in aseptic technique that introduces infectious organisms in the PD catheter, PD catheter exit site or tunnel infection with skin organisms that migrate into the peritoneal cavity, translocation of organisms from the gastrointestinal or genitourinary tract, or, in less than 1% of cases, hematogenous spread to the peritoneal cavity. After organisms enter the peritoneal cavity, polymorphonuclear leukocytes (PMNs) induce an inflammatory cascade, causing abdominal pain and cloudy dialysate.
PD-associated peritonitis is diagnosed in patients who meet at least 2 of the following 3 criteria: (1) clinical features consistent with peritonitis (ie, abdominal pain and/or cloudy PD fluid), (2) PD fluid white blood cell (WBC) count greater than or equal to 100 cells/μL with greater than or equal to 50% PMNs in dialysate that has dwelled in the abdomen for at least 2 hours; and (3) positive dialysate fluid culture result.3
A PD fluid WBC count of at least 100 cells/μL has a sensitivity of 80% and a specificity of 89% for the diagnosis of PD-associated peritonitis.4 PD fluid predominance of PMNs (≥50% of WBC) has a specificity of 97% for PD-associated peritonitis.5 PD effluent Gram stain results are positive in less than 10% of cases of suspected PD-associated peritonitis, but may help in the early identification of yeast or fungal peritonitis.3,4,6 PD fluid culture results are positive in approximately 72% to 86% of patients with PD-associated peritonitis.1 Negative PD fluid culture results are typically due to inappropriate sample collection or processing, but may rarely be due to mycobacteria, filamentous fungi, or other fastidious organisms.1,3 A peritoneal fluid PMN-to-lymphocyte ratio less than 15 can help distinguish mycobacterial infection from bacterial peritonitis (sensitivity, 81%; specificity, 70%; positive predictive value, 97%).7 If PD fluid dwells in the abdomen for more than 15 hours, the PD fluid WBC count may exceed 100 cells/μL in the absence of peritonitis, but is macrophage predominant.8
PD-associated peritonitis is typically caused by bacteria (Table 2). Cloudy PD fluid can occur in several conditions other than infectious peritonitis (eTable in the Supplement). Patients with clinical features consistent with PD-associated peritonitis should receive empirical broad-spectrum intraperitoneal antibiotics after PD fluid samples have been collected for Gram stain and culture. Intraperitoneal antibiotics are adjusted based on the antibiotic sensitivities of the organism(s) identified in the culture. Although intraperitoneal antibiotics are the preferred route of administration, the intravenous or oral route can be used if necessary to avoid delays in treatment if the intraperitoneal route is not an option. Approximately 80% of PD-associated peritonitis episodes resolve with intraperitoneal antibiotics; in the US, approximately 50% of these patients are treated as outpatients.1 PD catheter removal for peritonitis is recommended for refractory episodes (persistently cloudy PD fluid or PD fluid WBC count ≥100 cells/μL despite at least 5 days of appropriate intraperitoneal antibiotics), select relapsing, repeat or recurrent episodes of peritonitis, concurrent catheter infection and peritonitis with the same organism, and for all patients with fungal peritonitis.3,9 In North America, peritonitis-related death occurs in less than 5% of episodes of PD-associated peritonitis.9
According to the 2022 Medicare fee schedule, reimbursement is $5.60 for PD cell count analysis and $8.62 for PD fluid culture.
Application of Test Results to This Patient
The diagnosis of PD-associated peritonitis was confirmed by the presence of abdominal pain, cloudy dialysis fluid, and a PD fluid WBC count of 15 390 cells/μL with 93% PMN.
Alternative Diagnostic Testing Approaches
Leukocyte reagent strips used as a rapid screening test for PD-associated peritonitis have excellent diagnostic performance (sensitivity, 100%; specificity, 97%; positive predictive value, 95%).10 However, these tests are not frequently used because PD fluid cell counts can be rapidly obtained from clinical laboratory tests.
After PD fluid was collected for analysis, intraperitoneal cefazolin and ceftazidime were administered in a daily PD exchange with a 6-hour dwell time. The PD fluid culture grew methicillin-resistant Staphylococcus epidermidis, which was sensitive to vancomycin. Antibiotics were switched to intraperitoneal vancomycin and continued for 14 days. PD fluid analysis performed 3 days after presentation revealed a PD fluid WBC count of 64 cells/μL and results of the PD fluid culture were negative. The patient was counseled about aseptic PD exchange technique, and had no new episodes of peritonitis have occurred 1 year later.
Clinical Bottom Line
- Peritoneal dialysis (PD)–associated peritonitis affects approximately 30% to 40% of patients during their course of treatment with PD, and typically causes abdominal pain and cloudy PD fluid.
- PD-associated peritonitis is defined by presence of at least 2 of the following 3 criteria: clinical features consistent with peritonitis, PD fluid white blood cell count greater than or equal to 100 cells/μL with at least 50% polymorphonuclear leukocytes after a dwell time of at least 2 hours, or positive dialysis fluid culture.
- More than 95% of PD-associated peritonitis infections are caused by bacteria and, of these, approximately 80% resolve with intraperitoneal antibiotics.
