A series of patients undergo diagnostic paracentesis for newly developed or worsening asci… — USMLE Step 2 CK

A series of patients undergo diagnostic paracentesis for newly developed or worsening ascites. Based on the provided laboratory and clinical findings, match each patient's ascitic fluid profile with the most accurate underlying pathophysiologic mechanism and diagnosis.

Serum albumin: $3.2$ g/dL, Ascitic albumin: $1.5$ g/dL, Ascitic total protein: $1.8$ g/dL, Ascitic WBC: $180$ cells/mm $^3$ ( $30\%$ neutrophils). Physical examination reveals spider angiomata and caput medusae.Sinusoidal portal hypertension with impaired hepatic synthetic function (uncomplicated cirrhotic ascites)
Serum albumin: $3.8$ g/dL, Ascitic albumin: $2.2$ g/dL, Ascitic total protein: $3.1$ g/dL, Ascitic WBC: $150$ cells/mm $^3$ ( $20\%$ neutrophils). Physical examination reveals elevated jugular venous pressure and a pericardial knock.Post-hepatic portal venous congestion with preserved hepatic synthetic function (cardiac ascites)
Serum albumin: $3.5$ g/dL, Ascitic albumin: $2.8$ g/dL, Ascitic total protein: $4.2$ g/dL, Ascitic WBC: $800$ cells/mm $^3$ ( $70\%$ lymphocytes). The patient has a $2$ -month history of night sweats and weight loss.Exudative peritoneal inflammation secondary to chronic granulomatous infection (tuberculous peritonitis)
Serum albumin: $2.8$ g/dL, Ascitic albumin: $1.2$ g/dL, Ascitic total protein: $1.5$ g/dL, Ascitic WBC: $850$ cells/mm $^3$ ( $80\%$ neutrophils). The patient has chronic hepatitis C virus infection and presents with new-onset fever.Sinusoidal portal hypertension complicated by acute bacterial translocation (spontaneous bacterial peritonitis)
Serum albumin: $3.9$ g/dL, Ascitic albumin: $3.2$ g/dL, Ascitic total protein: $3.8$ g/dL. Ascitic fluid is milky-white with triglycerides of $650$ mg/dL. The patient is postoperative day $4$ following a retroperitoneal lymph node dissection.Direct extravasation of lipid-rich lymphatic fluid into the peritoneal cavity (chylous ascites)

Answer

Profile 1 matches uncomplicated cirrhotic ascites; Profile 2 matches cardiac ascites; Profile 3 matches tuberculous peritonitis; Profile 4 matches spontaneous bacterial peritonitis; Profile 5 matches chylous ascites.

The correct pairings rely on calculating and integrating the SAAG, total protein, and ANC. Profile 1 shows a high SAAG, low protein, and low ANC (uncomplicated cirrhosis). Profile 2 shows a high SAAG and high protein (cardiac ascites). Profile 3 shows a low SAAG with lymphocyte predominance (tuberculosis). Profile 4 shows a high SAAG, low protein, and an ANC

> 250

cells/mm

^3

(SBP). Profile 5 shows a low SAAG with severely elevated triglycerides (chylous ascites).

Step-by-Step Solution

Calculate the Serum-Ascites Albumin Gradient (SAAG) for each profile by subtracting the ascitic albumin from the serum albumin.

SAAG

\geq 1.1

g/dL indicates portal hypertension; SAAG

< 1.1

g/dL indicates an alternative exudative or non-portal hypertensive cause.

SAAG is the most accurate initial step in determining the broad etiology of ascites.

Evaluate the ascitic fluid total protein in profiles with SAAG

\geq 1.1

g/dL.

Ascitic protein

\geq 2.5

g/dL indicates preserved hepatic synthesis (post-hepatic/cardiac), while

< 2.5

g/dL indicates impaired synthesis (cirrhosis).

This differentiates the underlying source of portal hypertension.

Calculate the absolute neutrophil count (ANC) by multiplying ascitic WBC by the neutrophil percentage.

An ANC

\geq 250

cells/mm

^3

diagnoses spontaneous bacterial peritonitis.

Ascites can be complicated by acute infection, requiring immediate identification for antibiotic therapy.

Assess for unique markers such as lymphocyte predominance or markedly elevated triglycerides in low SAAG profiles.

Lymphocytes suggest tuberculous peritonitis; triglycerides

> 200

mg/dL indicate chylous ascites.

Specific etiologies of non-portal hypertensive ascites have distinct cellular and biochemical markers.

Key Concept

Interpretation of ascitic fluid analysis (SAAG, total protein, cell counts, and specific biochemistries) to determine the pathophysiology and etiology of ascites.

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