Spleen stiffness measurement rules out high-risk varices in patients with chronic portal vein thrombosis without cirrhosis.

Perform a diagnostic paracentesis in all patients with new-onset ascites that is accessible for sampling, and in any patient with cirrhosis and ascites who is emergently admitted to the hospital for any reason, to rule out SBP even in the absence of signs or symptoms of infection (up to one-third of SBP is asymptomatic). Also perform it whenever a patient with ascites develops signs, symptoms, or laboratory abnormalities suggestive of infection, and in patients with tense ascites and AKI to exclude SBP as the cause. LVP/paracentesis is safe even with coagulopathy: elevated prothrombin time (INR >1.5) or thrombocytopenia (platelets <50×10^9/L) is not a contraindication, and routine transfusion of clotting factors or platelets is NOT recommended, with possible exceptions in disseminated intravascular coagulation, or uremia with thrombocytopenia (where desmopressin may be considered, especially with prior bleeding). The initial laboratory investigation of ascitic fluid should include ascitic fluid neutrophil (PMN) count, ascitic fluid total protein, and ascitic fluid albumin plus a simultaneous serum albumin to calculate the serum-ascites albumin gradient (SAAG). Ascitic fluid culture is not part of that routine initial panel but should be obtained whenever SBP is being evaluated (routinely for inpatients and when secondary bacterial peritonitis is suspected); when cultured, inoculate ≥10 mL of fluid into aerobic and anaerobic blood culture bottles at the bedside, before the first dose of antibiotics. Amylase, cytology, glucose, LDH, and mycobacterial (AFB/ADA) or triglyceride testing are not routinely indicated and should be guided by clinical context (e.g., suspected pancreatic, malignant, secondary-bacterial, tuberculous, or chylous ascites). Interpret SAAG to classify the cause: SAAG ≥1.1 g/dL indicates portal hypertension (~97% accuracy), while SAAG <1.1 g/dL points to non-portal-hypertensive (peritoneal) causes such as peritoneal carcinomatosis, tuberculous peritonitis, nephrotic syndrome, or pancreatic/chylous ascites. Within high-SAAG ascites, use ascitic total protein to distinguish the source: total protein <2.5 g/dL suggests cirrhosis (also massive liver metastasis, late Budd-Chiari), whereas total protein ≥2.5 g/dL suggests a postsinusoidal/cardiac source (heart failure, portal vein thrombosis, sinusoidal obstruction syndrome, early Budd-Chiari), directing workup toward right-heart catheterization, hepatic-vein Doppler, and echocardiography. The diagnosis of SBP is established with an ascitic fluid absolute neutrophil (PMN) count >250/mm^3 (with or without a positive culture, and in the absence of a surgically treatable intra-abdominal source of infection). Spontaneous bacterial empyema (SBE) is the analogous spontaneous infection of a pre-existing hepatic hydrothorax, not a parapneumonic effusion, and is established by the same pleural fluid PMN count >250/mm^3, but only after pneumonia and other secondary causes of the effusion have been excluded; despite the term "empyema" it is managed as an infection with antibiotics, and a chest tube should NOT be placed.