Tests
1st tests to order
CBC
Test
Leukocytosis common with SBP, but may be absent. Worsening anemia may suggest gastrointestinal bleeding.
Result
leukocytosis, anemia
serum creatinine
Test
Hepatorenal syndrome may occur in patients with decompensated cirrhosis.
Result
may be elevated
LFT
Test
Used to establish baseline labs and monitor the health of the liver. In the patient with end-stage liver disease, bilirubin testing can be used to calculate a Model for End-Stage Liver Disease (MELD) score, MELD-Na, or Child-Pugh score to determine mortality rate and may assist in decision-making for SBP prophylaxis.
Result
In end-stage disease, liver enzymes and bilirubin often elevated; albumin decreased
prothrombin time/INR
Test
An elevated PT/INR is not a contraindication for diagnostic or therapeutic paracentesis.[108] Useful if the patient has GI hemorrhage or other bleeding complication. Is a component of Child-Pugh and MELD scoring systems to determine mortality rate.
Result
elevated
blood cultures
Test
As yield of peritoneal fluid culture is poor, blood cultures may assist in identifying the pathogenic organism. The Infectious Diseases Society of America (IDSA) recommends 2-3 sets of blood cultures for identification of concomitant bacteremia.[85]
Result
growth of causative organism
ascitic fluid appearance
Test
Subjective descriptions of ascitic fluid by laboratory technicians as "hazy," "cloudy," or "bloody" have a sensitivity of between 72% and 98% for the detection of SBP.[82][96]
Clinical impression, including an assessment of ascitic fluid appearance, should not be used to exclude the diagnosis.[82]
Demonstrates how to perform diagnostic and therapeutic abdominal paracentesis.
Result
"hazy," "cloudy," "bloody"
ascitic fluid absolute neutrophil count (ANC)
Test
ANC is diagnostic for SBP. If hemorrhagic ascites is present, subtract 1 neutrophil for every 250 red blood cells.
Although an ANC >500 cells/mm³ is more specific for the diagnosis of SBP, the danger of missing the diagnosis of SBP in a patient with an ANC count of 250-500 cells/mm³ is unacceptably high.[1]
Automated cell counters have been found to be equivalent to manual cell counts in the examination of ascitic fluid.[92][93][94]
Result
>250 cells/mm³
ascitic fluid culture
ascitic fluid protein, glucose, lactate dehydrogenase (LDH), pH
Test
Normal ascites should have low protein and LDH, and a glucose >50 mg/dL, and normal pH. A study comparing ascitic protein, glucose, and LDH in 6 patients with gastrointestinal perforation into their ascitic fluid (secondary peritonitis) and 32 patients with SBP found that all 6 of the patients with secondary peritonitis met at least two of the criteria for secondary peritonitis as follows: protein >1 g/dL; glucose <50 mg/dL; LDH >225 units/L. Only two of the patients with SBP fulfilled two of these criteria.[85][109][110]
Demonstrates how to perform diagnostic and therapeutic abdominal paracentesis.
Result
protein >1 g/dL; glucose <50 mg/dL; LDH >225 units/L raises likelihood of secondary peritonitis; ascitic fluid pH often decreased in SBP
Tests to consider
serum-ascites albumin gradient (SAAG)
Test
Calculated by subtracting the ascitic fluid albumin from the serum albumin in simultaneously obtained samples.[61] Indicated for new-onset ascites.
Result
>1.1 g/dL highly suggestive of portal hypertension, usually caused by liver disease; ≤1.1 g/dL suggests other causes of ascites
ascitic fluid carcinoembryonic antigen (CEA)
Test
Not routinely used, but can be useful in that an elevated level indicates secondary peritonitis. Therefore, if level is normal (<5 nanograms/mL), it raises the likelihood of secondary peritonitis.[98]
Result
<5 nanograms/mL
ascitic fluid alkaline phosphatase
Test
Not routinely used, but can be useful in that an elevated level indicates secondary peritonitis. Therefore, if level is normal (<240 units/L) it raises the likelihood of secondary peritonitis.[98]
Result
<240 units/L
ascitic fluid AFB stain and culture, fungal culture, microscopy for ova/parasites
Test
Can help diagnose the cause of peritonitis.[85]
Result
positive = abnormal
ascitic fluid lactoferrin
Test
Can help identify SBP in a cirrhotic patient with ascites. Sensitivity is 96% and specificity is 97% for the detection of SBP.[111]
Not routinely performed, but if a qualitative bedside assay can be developed, it might significantly reduce the time to diagnosis.[99]
Demonstrates how to perform diagnostic and therapeutic abdominal paracentesis.
Result
level elevated in SBP; an elevated lactoferrin in a cirrhotic patient without SBP can indicate a developing hepatic carcinoma
CT scan abdomen
Test
May be considered in patients with findings suggestive of secondary peritonitis, such as bile-stained fluid, polymicrobial growth on ascites fluid culture, no clinical improvement despite appropriate antibiotics for 48 hours, and no history of liver disease or malignancy to explain the ascites. May demonstrate free air.[103][104]
Result
demonstrates diffuse ascites; excludes pneumoperitoneum in patients with secondary peritonitis
Emerging tests
highly-sensitive leukocyte esterase reagent strip testing of ascitic fluid (Periscreen)
bedside (standard urine) leukocyte esterase reagent strip testing of ascitic fluid
Test
Can be done at the bedside within 2 minutes.
The reagent strip is dipped into ascitic fluid, and after 60-120 seconds the result is analyzed according to the colorimetric scale for that reagent strip. Most studies used a strip color that gives a positive result as corresponding to between 15 (1+) and 125 leukocytes/mL (3+).
One meta-analysis found sensitivities ranging from 45% to 100% and specificities ranging from 81% to 100%.[102]
Low sensitivity demonstrates that bedside (standard urine) leukocyte esterase reagent strip testing is not suitable for rapidly ruling out SBP. However, the high specificity suggests that it has a role in the rapid diagnosis of SBP, facilitating prompt administration of antibiotic therapy.
Result
elevated leukocytes measured by comparison with a color strip
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