Step 1: what comes next?
Recognize a trigger
Hospital admission, abdominal symptoms, fever, hypotension, kidney injury, gastrointestinal bleeding, worsening jaundice, or encephalopathy should lower the threshold.
GI
Spontaneous Bacterial Peritonitis
In cirrhosis, quiet symptoms can conceal an infected ascitic compartment.
- Recognize subtle SBP presentations and obtain ascitic fluid before antibiotics when feasible.
- Apply the PMN threshold, culture technique, and empiric antibiotic strategy.
- Select albumin and prophylaxis appropriately and distinguish secondary peritonitis.
Rounds dashboard
See the whole liver patient
The dashboard keeps injury pattern, function, complications, and next action visible together.
Quick check
A 67-year-old with cirrhosis and ascites is admitted for new confusion and acute kidney injury. Temperature is 37.2 C, and the abdomen is mildly distended without rebound.
What is the most important immediate diagnostic step?
Reason it through
- Can SBP be afebrile?Yes. Presentation may be subtle.
- Which organ changes can be the clue?New encephalopathy, kidney injury, hypotension, or worsening liver tests.
- What test establishes the treatment threshold?Ascitic absolute PMN count.
Thresholds that trigger action
The numbers are simple; missing the clinical context is the danger.
The absolute PMN count, not total leukocytes alone, determines the diagnostic treatment threshold.
Failure of the PMN count to fall substantially after therapy raises concern for resistant organisms or a secondary source.
Place the thresholds along the escalation axis.
Two or more of ascitic protein above 1 g/dL, glucose below 50 mg/dL, and LDH above serum upper limit support secondary peritonitis.
Spontaneous versus surgically sourced infection
Both can produce neutrocytic ascites, but their source and trajectory differ.
SBP is infection of ascitic fluid without a treatable intra-abdominal source, usually with a single enteric organism.
Secondary bacterial peritonitis arises from perforation, abscess, ischemia, or another source that requires imaging and source control.
Compare the patterns that direct treatment.
Ascitic PMN count is at least 250/mm3, culture is often monomicrobial, and no surgically treatable source is found.
PMN count is at least 250/mm3 but culture is negative; manage as SBP after considering other causes of neutrophilia.
Culture is positive with PMN below 250/mm3; symptomatic patients require treatment, while selected asymptomatic patients need prompt repeat sampling.
Polymicrobial culture, focal peritoneal signs, Runyon-type chemistry, free air, a structural lesion, or poor PMN response should trigger imaging and source control.
Do not let a negative culture overrule an ascitic PMN count of 250/mm3 or more.
The first hours of suspected SBP
Fast sampling preserves diagnostic yield and fast treatment protects kidney and brain function.
Perform paracentesis before antibiotics when this does not delay resuscitation; send cell count with differential and chemistry.
Inoculate ascitic fluid directly at the bedside into aerobic and anaerobic blood-culture bottles to improve organism recovery.
Order the bedside workflow.
Step 2: what comes next?
Perform diagnostic paracentesis
Obtain fluid promptly; coagulopathy or thrombocytopenia alone usually does not justify delay.
Step 3: what comes next?
Inoculate cultures at bedside
Place fluid directly into aerobic and anaerobic blood-culture bottles before antibiotics.
Step 4: what comes next?
Calculate the absolute PMN count
Use the differential; a PMN count of at least 250/mm3 is the treatment threshold.
Step 5: what comes next?
Start empiric antibiotics
Use a third-generation cephalosporin for typical community-acquired disease and tailor broader therapy to nosocomial or resistant-risk ecology.
Step 6: what comes next?
Reassess response
Review cultures and clinical course; repeat paracentesis near 48 hours when response is uncertain or secondary peritonitis is a concern.
Treat before the culture finishes
The PMN result drives initial therapy; culture refines it.
Cefotaxime or ceftriaxone is standard empiric therapy for uncomplicated community-acquired SBP, with local antibiograms guiding alternatives.
Healthcare-associated infection, recent broad antibiotics, prior resistant organisms, or severe sepsis may require broader initial coverage followed by rapid de-escalation.
Select the correct immediate action.
PMN at least 250/mm3 means treat; anatomy decides whether antibiotics alone are enough.
Sample the compartment, protect the circulation
Ascitic infection can destabilize organs far beyond the abdomen.
Inflammation worsens splanchnic vasodilation and effective arterial underfilling, increasing acute kidney injury and hepatorenal risk.
Systemic signs may be absent because advanced cirrhosis blunts inflammatory responses.
Map the finding to the organ-level consequence.
1Peritoneal cavity
Diagnostic fluid provides the PMN count, culture, albumin, protein, glucose, and LDH data needed to classify infection.
2Kidney
Rising creatinine or BUN identifies higher risk and strengthens the case for adjunctive albumin in SBP.
3Brain
New encephalopathy may be the only obvious sign of infection.
4Circulation
Hypotension and vasodilation can progress despite little abdominal tenderness.
5Bowel or biliary source
Focal pain, polymicrobial culture, abnormal ascitic chemistry, or poor response points toward secondary peritonitis and source control.
Albumin and prevention are selected, not automatic
Adjuncts matter most when the patient has renal-risk physiology or a proven recurrence risk.
For SBP with kidney dysfunction or marked hepatic dysfunction, IV albumin lowers renal failure and mortality risk; a commonly used regimen is 1.5 g/kg on day 1 and 1.0 g/kg on day 3.
Survivors of SBP need long-term secondary antibiotic prophylaxis. Agent selection should reflect availability, contraindications, and local resistance.
Reveal who benefits and why.
Use adjunctive albumin with antibiotics when appropriate.
These classic risk features identify patients most likely to benefit.
Begin secondary prophylaxis after treatment.
Recurrence risk is high without prophylaxis.
Give short-course antibiotic prophylaxis, commonly ceftriaxone.
Bleeding sharply increases infection risk.
Do not assume prophylaxis is automatic.
Primary prophylaxis is reserved for selected high-risk patients after weighing resistance and adverse effects.
Escalate the search for secondary peritonitis.
Obtain urgent imaging, broaden coverage, and pursue source control.
Stage 1 of 3: Overview
Overview
Spontaneous Bacterial Peritonitis
Fast sampling preserves diagnostic yield and fast treatment protects kidney and brain function.
Rounds question
Name today’s management pivot
Choose the clue that changes what the team does on this round.
What is the most important immediate diagnostic step?
- Key finding. A 67-year-old with cirrhosis and ascites is admitted for new confusion and acute kidney injury. Temperature is 37.2 C, and the abdomen is mildly distended without rebound.
- Answer. Diagnostic paracentesis now
- Why. SBP may present only with encephalopathy or kidney injury, and hospitalized patients with ascites need prompt fluid testing.
- Board rule. In hospitalized cirrhotic ascites, paracentesis is an early vital action.
Run the liver cases
Five cirrhotic patients test subtle recognition, fluid interpretation, empiric care, albumin selection, and recurrence prevention.
Cross out premature plans and highlight the finding that changes management. Each case separates injury, function, and complication.
A 70-year-old with cirrhosis is admitted for worsening creatinine and mild confusion. Paracentesis yields 600 nucleated cells/mm3 with 60% neutrophils; culture is pending.
What is the best interpretation and action?
Reason it through
- How is the PMN count calculated?Multiply total nucleated cells by the neutrophil fraction.
- What is 600 times 0.60?360 PMN/mm3.
- What does 360 trigger?Immediate empiric antibiotic therapy.
How is the PMN count calculated?What is 600 times 0.60?
- How is the PMN count calculated?Multiply total nucleated cells by the neutrophil fraction.
- What is 600 times 0.60?360 PMN/mm3.
- What does 360 trigger?Immediate empiric antibiotic therapy.
A 62-year-old with community-acquired SBP is hemodynamically stable and has no prior resistant isolate. Ascitic PMN is 780/mm3.
Which empiric regimen is most appropriate?
Reason it through
- Is this community- or hospital-acquired?The stem supports community-acquired infection.
- Is there a resistant-organism clue?No prior isolate or recent exposure is given.
- What drug class fits?A third-generation cephalosporin.
Is this community- or hospital-acquired?Is there a resistant-organism clue?
- Is this community- or hospital-acquired?The stem supports community-acquired infection.
- Is there a resistant-organism clue?No prior isolate or recent exposure is given.
- What drug class fits?A third-generation cephalosporin.
A 65-year-old with SBP has bilirubin 5.2 mg/dL, BUN 36 mg/dL, and creatinine 1.4 mg/dL. Ceftriaxone has been started.
Which adjunct is most appropriate?
Reason it through
- Which values signal renal risk?BUN 36 and creatinine 1.4 exceed classic risk thresholds.
- Which hepatic value adds risk?Bilirubin 5.2 mg/dL.
- What does albumin protect?It supports effective circulation and reduces renal failure risk.
Which values signal renal risk?Which hepatic value adds risk?
- Which values signal renal risk?BUN 36 and creatinine 1.4 exceed classic risk thresholds.
- Which hepatic value adds risk?Bilirubin 5.2 mg/dL.
- What does albumin protect?It supports effective circulation and reduces renal failure risk.
A patient treated for presumed SBP has worsening focal abdominal pain. Ascitic culture grows two enteric organisms; protein is 1.8 g/dL, glucose 34 mg/dL, and LDH exceeds the serum upper limit.
What is the most appropriate next step?
Reason it through
- What does polymicrobial culture suggest?A breached or inflamed intra-abdominal source.
- Which chemistry triad is present?High protein, low glucose, and high LDH.
- Why are antibiotics insufficient?A structural source may require drainage or surgery.
What does polymicrobial culture suggest?Which chemistry triad is present?
- What does polymicrobial culture suggest?A breached or inflamed intra-abdominal source.
- Which chemistry triad is present?High protein, low glucose, and high LDH.
- Why are antibiotics insufficient?A structural source may require drainage or surgery.
A 57-year-old completes treatment for a first confirmed episode of SBP and is ready for discharge. Kidney function has returned to baseline.
Which prevention plan is indicated?
Reason it through
- Is this primary or secondary prevention?It is secondary prevention after proven SBP.
- Why continue an antibiotic?Recurrence risk is high.
- What modifies agent choice?Local resistance, prior cultures, adverse effects, interactions, and availability.
Is this primary or secondary prevention?Why continue an antibiotic?
- Is this primary or secondary prevention?It is secondary prevention after proven SBP.
- Why continue an antibiotic?Recurrence risk is high.
- What modifies agent choice?Local resistance, prior cultures, adverse effects, interactions, and availability.
Rapid review
Three questions to check
What is the most important immediate diagnostic step?
Diagnostic paracentesis now. SBP may present only with encephalopathy or kidney injury, and hospitalized patients with ascites need prompt fluid testing.
How is the PMN count calculated?
Multiply total nucleated cells by the neutrophil fraction.
What is 600 times 0.60?
360 PMN/mm3.
Medically reviewed
Fatima Ali, DO
PGY-1 Resident Physician in Psychiatry
University Hospitals, Columbia
DO from Kansas City University
Resident physician and founding medical reviewer at Bone Wizardry, focused on clinical accuracy, clear diagnostic reasoning, and practical board-oriented teaching across the curriculum.
Languages: English, Urdu
Primary reviewerFull physician profile
Medically reviewed
Sources
- Diagnosis, Evaluation, and Management of Ascites, Spontaneous Bacterial Peritonitis and Hepatorenal Syndrome2021
- Ascites2025
Bone Wizardry is a study resource for medical students. It is not medical advice.