Body Fluid Lab Essentials
Learn how to obtain body fluid samples, order the right tests, and quickly diagnose your patient’s problem with this epic course.
2 CME credits
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.
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 per cubic millimeter. 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. 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 grams per deciliter, and a transudate if it is below 2.5 grams per deciliter.
However, exudate transudate system of ascitic fluid classification has been replaced by the serum to ascites albumin gradient, which is a more useful measure for determining whether portal hypertension is present. 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 grams per deciliter, predicts that the patient has portal hypertension with 97 percent accuracy. A serum to ascites albumin gradient less than 1.1 grams per deciliter indicates that the patient does not have portal hypertension.
A serum to ascites albumin gradient equal to or greater than 1.1 grams per deciliter 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 grams per deciliter, whereas in cardiac ascites, it is greater than or equal to 2.5 grams per deciliter.
Lastly, note that in patients with nephrotic ascites, the serum to ascites albumin gradient is less than 1.1 grams per deciliter, and the total protein in the ascites is less than 2.5 grams per deciliter.