Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (134 page)

   Laboratory Findings

Albumin
: Almost always ≥1.1 g/dL in cirrhosis (most common cause), alcoholic hepatitis, massive liver metastases, fulminant hepatic failure, portal vein thrombosis, Budd-Chiari syndrome, cardiac ascites, fatty liver, acute fatty liver of pregnancy, myxedema, mixed (e.g., cirrhosis with peritoneal TB). May be falsely low if serum albumin <1.1 g/dL or the patient in shock. May be falsely high with chylous ascites (lipid interferes with albumin assay). Albumin levels <1.1 g/dL in >90% of cases of peritoneal carcinomatosis (most common cause), TB, pancreatic or biliary ascites, nephrotic syndrome, bowel infarction or obstruction, and serositis in patients without cirrhosis.

Ascites fluid findings
: AF total protein >2.5 mg/dL in cancer is only 56% accurate because of high protein content in 12–19% of these ascites as well as changes caused by albumin infusion and diuretic therapies. AF/serum albumin ratio <0.5 in cirrhosis (>90% accuracy). AF/serum ratio of LD (>0.6) or protein (>0.5) is not more accurate (approximately 56%) than only total protein for diagnosis of exudate. AF cholesterol <55 mg/dL in cirrhosis (94% accuracy). Albumin gradient (serum albumin minus AF albumin) reflects portal pressure. Total WBC count is usually <300/μL (50% of cases) and PMN <25% (50% of cases).

Core laboratory
: Liver function tests are abnormal.

Other
: Cirrhosis findings are similar with or without hepatocellular carcinoma. Cardiac ascites is associated with a blood–AF albumin gradient >1.1 g/dL, but malignant AF shows blood–AF albumin gradient <1.1 g/dL in 93% of cases.

INFECTED ASCITIC FLUID

   Laboratory Findings

Culture
: AF in blood culture bottles has 85% sensitivity.

Ascites fluid findings
:

   WBC count >250/μL: sensitivity = 85%, specificity = 93%, and neutrophils >50% are presumptive of bacterial peritonitis.

   pH <7.35 and arterial–AF pH difference >0.10; both these findings are virtually diagnostic of bacterial peritonitis and the absence of the above findings virtually excludes bacterial peritonitis.

   Lactate >25 mg/dL and arterial–AF difference >20 mg/dL are often present. LD is markedly increased. Phosphate, potassium, and gamma-glutamyltransferase may also be increased. Glucose is unreliable for diagnosis. Total protein <1.0 g/dL indicates high risk for SBP.

   Gram stain shows few bacteria in spontaneous bacterial peritonitis (SBP) but many when caused by intestinal perforation. Culture sensitivity = 50% for SBP and approximately 80% for secondary peritonitis. TB acid-fast stain sensitivity = 20–30% and TB culture sensitivity = 50–70%.

SECONDARY PERITONITIS

   This condition shows polymicrobial infection, total protein >1.0 g/dL, AF/LD greater than serum upper limit of normal, and glucose <50 mg/dL compared with spontaneous bacterial peritonitis (SPB).

   Prevalence of SBP 15%; due to
Escherichia coli
approximately 50%,
Klebsiella
, and other gram-negative bacteria; gram-positive bacteria approximately 25% (especially streptococci).

CONTINUOUS AMBULATORY PERITONEAL DIALYSIS

Monitor dialysate for the following
:

   
Infection
: Peritonitis is defined as WBC count >100/μL, usually with >50% PMNs (normal is <50 WBC/μL, usually mononuclear cells), or positive Gram stain or culture (most prevalent: coagulase-negative staphylococci,
Staphylococcus aureus
,
Streptococcus
sp.; multiple organisms, especially mixed aerobes and anaerobes occur with bowel perforation). Successful therapy causes fall in WBC count within first 2 days and a return to <100/μL in 4–5 days; differential returns to predominance of monocytes in 4–7 days with increased eosinophils in 10% of cases. Patients check outflow bags for turbidity. Turbid dialysate can occur occasionally without peritonitis during the first few months of placing catheter (due to catheter hypersensitivity) with WBC count 100–8,000/μL, 10–95% eosinophils, sometimes increased PMNs, and negative cultures. Occasional RBCs may be seen during menstruation or with ovulation at midcycle.
Because of low WBC decision level, manual hemocytometer count rather than an automated instrument must be used.

   
Metabolic change
: Assay dialysate for creatinine and glucose; calculate ultra-filtrate volume by weighing dialysate fluid after 4-hour dwell time and subtracting it from preinfusion weight using specific gravity of 1.0.