What is a Response Tap in Ascites?
A "response tap" refers to a follow-up diagnostic paracentesis performed 48 hours after initiating antibiotic therapy for suspected spontaneous bacterial peritonitis (SBP) to confirm treatment efficacy by demonstrating a decrease in ascitic fluid neutrophil count. 1
Purpose and Timing
The response tap is performed to verify that antibiotic therapy is effectively treating SBP, as evidenced by a declining neutrophil count in the ascitic fluid. 1
This follow-up paracentesis should be done 48 hours after starting antibiotics in patients with an initial ascitic neutrophil count >250 cells/mm³. 1
Failure to demonstrate a decrease in neutrophil count on the response tap suggests antibiotic resistance, inadequate coverage, or secondary bacterial peritonitis (indicating a surgically treatable intra-abdominal source requiring different management). 1
Clinical Context
SBP is diagnosed when the ascitic neutrophil count exceeds 250 cells/mm³ in the absence of an intra-abdominal surgically treatable source of infection. 1
Approximately 15% of hospitalized cirrhotic patients with ascites have SBP, making diagnostic paracentesis mandatory on admission and whenever clinical deterioration occurs (fever, abdominal pain, encephalopathy, renal impairment, or unexplained leukocytosis). 1, 2
Patients with "culture-negative neutrocytic ascites" (neutrophil count >250 cells/mm³ with negative cultures) should be treated identically to culture-positive SBP, as both carry similar morbidity and mortality. 1
Interpretation of Response Tap Results
A decreasing neutrophil count on the response tap indicates appropriate antibiotic selection and treatment response, allowing continuation of the current antibiotic regimen for the full 5-day course. 1
A stable or rising neutrophil count suggests treatment failure, necessitating broader antibiotic coverage or investigation for secondary bacterial peritonitis from a perforated viscus or other intra-abdominal pathology. 1
If polymicrobial infection is identified on culture, this strongly suggests secondary bacterial peritonitis rather than SBP, requiring surgical evaluation and different management. 1
Common Pitfalls to Avoid
Do not delay the response tap beyond 48 hours, as early identification of treatment failure is critical for patient survival given the 20% in-hospital mortality of SBP even with prompt treatment. 1
Do not skip the response tap in patients who appear clinically improved, as clinical symptoms may not reliably correlate with microbiological response, and subclinical treatment failure can lead to complications. 1
Do not withhold the response tap due to coagulopathy concerns, as paracentesis can be safely performed despite abnormal coagulation parameters, with bleeding complications occurring in <1 in 1,000 procedures. 1, 3, 2