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Difficulty: MediumInterpreting Laboratory Results

A 55-year-old man is evaluated in the emergency department for progressive abdominal distension and bilateral lower extremity edema over the past 3 weeks. He has a history of chronic hepatitis C infection and alcohol use disorder. On physical examination, his vital signs are stable. The abdomen is distended with prominent shifting dullness and a positive fluid wave. A diagnostic paracentesis is performed, yielding clear, yellow fluid.

Concurrent laboratory studies show:

Serum:
Albumin: 3.1 g/dL
Total protein: 6.5 g/dL
Total bilirubin: 2.5 mg/dL

Ascitic fluid:
Albumin: 1.3 g/dL
Total protein: 2.2 g/dL
Leukocyte count: 210/mm³ (10% neutrophils, 90% mononuclear cells)

To help determine the etiology of the patient's ascites, the physician calculates the serum-ascites albumin gradient (SAAG). What is the patient's SAAG in g/dL?

Answer: 1.8 g/dL

Answer

1.8
The patient's SAAG is 1.8 g/dL. SAAG is correctly calculated by subtracting the ascitic fluid albumin concentration (1.3 g/dL) from the serum albumin concentration (3.1 g/dL). A SAAG of 1.1 g/dL or greater indicates that the ascites is driven by portal hypertension (such as from hepatic cirrhosis), which aligns with this patient's history of hepatitis C and alcohol use.

Step-by-Step Solution

1
Identify the formula for calculating SAAG.
SAAG = Serum Albumin - Ascitic Fluid Albumin
The SAAG formula is required to classify the ascites as related to portal hypertension or another etiology.
2
Locate the patient's serum albumin and ascitic fluid albumin levels from the laboratory data.
Serum albumin is 3.1 g/dL, and ascitic fluid albumin is 1.3 g/dL.
Accurate identification of the specific albumin values is necessary, avoiding confusion with total protein levels.
3
Subtract the ascitic fluid albumin from the serum albumin.
3.1 - 1.3 = 1.8
Executing the subtraction provides the final SAAG value.

Key Concept

The serum-ascites albumin gradient (SAAG) is calculated by subtracting the ascitic fluid albumin from the serum albumin, with a value ≥ 1.1 g/dL indicating portal hypertension.
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Interpreting Laboratory Results

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