Approach to ascites: Clinical sciences

Ascites refers to an abnormal collection of fluid in the peritoneal cavity, which can be a sign of various underlying conditions. In some cases, ascites can arise in the absence of portal hypertension, which is typically seen in conditions such as peritoneal carcinomatosis; pancreatic ascites, protein-losing enteropathy, and nephrotic syndrome.

More commonly, ascites is associated with portal hypertension, which can occur due to prehepatic, hepatic, and posthepatic causes. The most common prehepatic cause is portal vein thrombosis; while common hepatic causes include cirrhosis, infiltrative liver disease, and acute liver failure. Finally, important posthepatic causes include right-sided heart failure, constrictive pericarditis, and pulmonary hypertension.

Now, when approaching a patient with new ascites, you should first obtain focused history and physical examination, as well as labs, including CBC, CMP, and coagulation profile. History typically includes progressive abdominal distension; while physical exam reveals bulging flanks, a palpable fluid wave, and shifting dullness to percussion.

Additionally, order an abdominal ultrasound, which can help you detect free fluid in the peritoneal cavity, which is commonly seen as an anechoic space.

Next, obtain a diagnostic paracentesis to remove a small amount of ascitic fluid for analysis. Initial tests on the ascitic fluid include albumin, total protein, and cell count with differential. With these values, calculate the serum ascites albumin gradient, or SAAG for short, by subtracting the ascites albumin from the serum albumin. The SAAG results will help you determine if portal hypertension is present or absent. Moreover, SAAG less than 1.1 means there’s no portal hypertension, so your next step is to assess the ascitic fluid WBC count and differential.

Elevated WBCs in ascitic fluid with predominant lymphocytes should make you think of peritoneal disease, so test ascitic fluid for TB cultures and order cytology. Positive cultures confirm the diagnosis of peritoneal tuberculosis; while positive cytology for malignant cells confirms the diagnosis of peritoneal carcinomatosis. Keep in mind that peritoneal carcinomatosis can be caused by a primary cancer of the peritoneum, but more often it happens when cancer metastasizes to the peritoneum.

Ok, let’s say the ascitic fluid has elevated WBCs, but the differential reveals a neutrophilic predominance. In this case, you should consider pancreatic ascites or secondary bacterial peritonitis. Individuals with pancreatic ascites may have a history of chronic pancreatitis, or they may have suffered recent abdominal trauma.

To differentiate the two, measure ascitic amylase level and order ascitic fluid cultures. High amylase confirms the diagnosis of pancreatic ascites. On the other hand, positive ascitic fluid cultures for more than one pathogen, or in other words, positive polymicrobial cultures, confirm the diagnosis of secondary bacterial peritonitis. Secondary bacterial peritonitis occurs when bacteria from an underlying intraabdominal infection spread to the peritoneal cavity.

Finally, let’s take a look at patients that present with normal WBC count with lymphocyte predominance. If your patient presents with ascites and a history of diarrhea, steatorrhea, or abdominal bloating, in combination with pitting edema, consider protein-losing enteropathy.

In this case, order a 24-hour stool alpha-1 antitrypsin test to evaluate for excessive protein loss in the stool. Elevated alpha-1 antitrypsin confirms the diagnosis of protein-losing enteropathy.

But, what if your patient presents with a history of frothy urine and facial edema? In this case, consider nephrotic syndrome. To confirm the diagnosis, you should order a urinalysis and 24-hour urine protein. Urinalysis in a patient with nephrotic syndrome will show greater than 3.5 g of protein per 24 hours, as well as lipiduria.

Now, let’s go back to the SAAG and take a look at individuals with SAAG equal to or greater than 1.1, which is suggestive of portal hypertension. In these individuals, your next step is to assess the ascitic fluid total protein and determine whether or not the cause of portal hypertension is a liver problem.

If the ascitic fluid total protein is equal to or greater than 2.5 g/dL, there’s a low likelihood of liver conditions, so consider posthepatic causes.

These individuals typically report dyspnea on exertion, while their physical exam usually reveals jugular venous distention, bilateral lower extremity edema, and hepatomegaly. If your patient presents with these findings, order a transthoracic echocardiogram, or TTE for short. TTE can help you detect elevated pressure in the right side of the heart, which is associated with increased central venous pressure and conditions such as right-sided heart failure, constrictive pericarditis, and pulmonary hypertension.