Analyzing the cell count and protein concentration in ascites

The cell count with differential is the single most useful test performed on ascitic fluid to evaluate for infection. In this video, you will learn how cell counts and protein concentrations help us diagnose the cause of ascites, how to figure out the serum-ascites albumin gradient (SAAG), and why it matters so much.

Learn how to obtain bodily fluid samples, order the right tests, and quickly diagnose your patient’s problem with this course. From time to time, we send various bodily fluids to the laboratory—but are we ordering the right tests on these fluids to come to an accurate diagnosis? After this course, you will be comfortable ordering and interpreting bodily fluid analyses. You will understand the clinical implications of lab abnormalities and will know what to do about them.

Ascitic fluid cell count and infection

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In this Medmastery lesson, we will find out how the cell count and protein concentration helps us diagnose the cause of ascites. The cell count with differential is the single most useful test performed on ascitic fluid to evaluate for infection and should be ordered on every ascites specimen, including therapeutic paracentesis specimen. Antibiotic treatment should be considered in any patient with a corrected neutrophil count equal to or greater than 250 / mm³.

Correcting the cell count after a traumatic tap

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The presence of blood in a sample suggests a traumatic tap may have occurred. In this case, the white blood cells in the sample could come from two sources: the original ascitic fluid or the blood resulting from the trauma related to the procedure. The lab will perform a calculation to correct the white blood cell count in bloody samples.

Ascitic fluid protein and exudate classification

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Remember that the protein concentration determines if the fluid is an exudate or transudate. Ascitic fluid is classified as an exudate if the total protein concentration is equal to or greater than 2.5 g / dL and a transudate if it is below 2.5 g / dL. However, exudate–transudate system of ascitic fluid classification has been replaced by the serum-to-ascites albumin gradient, which is a more useful measure for determining whether portal hypertension is present.

Calculating and interpreting the serum-to-ascites albumin gradient

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The serum-to-ascites albumin gradient is easily calculated by taking the serum albumin value and subtracting the ascitic fluid albumin value. Both values should be obtained on the same day. The presence of a serum-to-ascites albumin gradient greater than or equal to 1.1 g / dL predicts that the patient has portal hypertension with 97% accuracy. A serum-to-ascites albumin gradient less than 1.1 g / dL indicates that the patient does not have portal hypertension.

Distinguishing cirrhotic, cardiac, and nephrotic ascites

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A serum-to-ascites albumin gradient equal to or greater than 1.1 g / dL can be due to cirrhosis or cardiac cause of ascites. The total protein concentration may help differentiate whether ascites results from cirrhosis or from a cardiac cause. In the case of cirrhosis, the total protein is less than 2.5 g / dL, whereas in cardiac ascites, it is greater than or equal to 2.5 g / dL. Lastly, note that in patients with nephrotic ascites, the serum-to-ascites albumin gradient is less than 1.1 g / dL, and the total protein in the ascites is less than 2.5 g / dL.