Healthcare and Medicine Reference
Sampling: Ascitic Tap
Centre for Liver Research, University of Birmingham, Birmingham, UK
By the end of this chapter you should be able to:
understand the indications for performing an ascitic tap
be able to examine for and assess the extent of ascites
describe how to perform an ascitic tap
interpret the results of an ascitic tap.
Evaluation of new-onset ascites
A diagnostic ascitic tap is a crucial part of the work-up of a patient
with new-onset ascites. Analysis of the fl uid can help decide the
most appropriate further investigations to perform in order to
determine the cause of the ascites.
Assessment of established ascites
In patients with established ascites who have an unexplained
change in clinical condition, an ascitic tap is essential to investigate
for the presence of spontaneous bacterial peritonitis. Assessment of
protein concentration can also indicate new pathology (e.g. raised
protein concentration in Budd-Chiari syndrome on a background
of chronic liver disease).
Figure 8.1 A patient with an obvious distended abdomen.
Many patients who require a diagnostic ascitic tap have chronic liver
disease with deranged clotting. There is evidence that performing
a diagnostic tap with a small gauge needle (e.g, a green needle) is
safe in the presence of low platelets or elevated INR/PT.
In the presence of active fi brinolysis or DIC a diagnostic tap
A diagnostic ascitic tap should not be attempted in the presence of
the following conditions:
acute abdomen requiring surgical intervention
should not be attempted.
Clinical detection of ascites
Ascites is the accumulation of fl uid within the peritoneal cavity.
The presence of ascites can usually only be confi rmed clinically at
volumes greater than 1500 mL. It is signifi cantly more diffi cult to
reliably detect ascites in those with central obesity.
Initial inspection is important, as the shape of the abdomen will give
clues as to the presence of ascites. With the patient supine, accumu-
lated fl uid will cause bulging of the fl anks; on standing the fl uid will
accumulate in the lower abdomen and pelvis (Figure 8.1). Bulging of
the fl anks may also be caused by subcutaneous fat in obese patients;
further examination is required to distinguish fat from fl uid.
urinary retention/distended bladder
abdominal wall infection
If required, it may be possible to perform a tap under direct vision
using ultrasound guidance.
dilated loops of bowel (e.g. volvulus).