An ascitic tap (diagnostic paracentesis) is one of the most important bedside procedures in patients with cirrhosis.

It is:

Quick
Low risk
High yield

And it can save lives by diagnosing SBP early.

This guide focuses on how to perform it safely and confidently on the ward.

What is an ascitic tap?

A diagnostic ascitic tap is:

Removal of a small amount of ascitic fluid (usually 20–50 mL) for testing.

Used to:

Diagnose SBP
Identify cause of ascites
Guide management

This is different from large volume paracentesis (drain).

When should you do an ascitic tap?

In real NHS practice:

Always tap if:

New ascites
Known cirrhosis + admission to hospital
Fever
Abdominal pain
Confusion/encephalopathy
AKI
Raised inflammatory markers
“Generally unwell” with ascites

Golden rule:

Any unwell patient with ascites → tap early

Do not wait for ultrasound or seniors if you are competent.

When NOT to delay the tap

Common mistake:
“Let’s wait for imaging or the day team”

This delays diagnosis of SBP.

Ascitic tap is:

Lower risk than missing SBP

Tap first, scan later if needed.

First priority = is it safe to proceed?

Before starting:

Check:

Patient stable?
No obvious peritonitis requiring surgery?
Platelets not extremely low
INR not severely deranged (mild derangement is common and usually OK)
Bladder empty

True contraindications are rare.

If unsure → discuss with senior, but don’t overthink.

✅ Equipment checklist (ward practical)

Have everything ready first:

Sterile gloves
Dressing pack
Chlorhexidine
Local anaesthetic (lidocaine)
Needle + syringe
Ascitic tap needle/cannula
Sample bottles:
- EDTA (cell count)
- Culture bottles
- Biochemistry bottle
Gauze + dressing

Being organised prevents contamination.

✅ Step-by-step: How to perform an ascitic tap

Step 1 – Position the patient

Supine or slightly tilted
Comfortable
Expose abdomen fully

Ascitic fluid collects laterally → easier to access.

Step 2 – Choose the site

Most common safe site:
👉 Left or right lower quadrant

About:

2–3 cm medial and superior to ASIS

Avoid:

Midline (vessels, bowel, varices)
Surgical scars
Visible veins
Cellulitis

If available → ultrasound guidance is ideal but not essential.

Step 3 – Sterile prep

Clean skin well
Sterile field
Gloves on

Infection risk is low but avoid contamination.

Step 4 – Local anaesthetic

Infiltrate skin and deeper tissues
Aspirate as you go
Wait 30–60 seconds

Patients tolerate much better if you do this properly.

Step 5 – Insert needle

Advance slowly while aspirating
You’ll feel a “give”
Fluid appears in syringe

Do not push aggressively.

If no fluid:

Slightly adjust angle
Don’t keep stabbing

Step 6 – Collect samples

Collect enough fluid for:

Send:

Cell count (most important)
Culture (in blood culture bottles)
Albumin (for SAAG)
± protein, cytology if indicated

Order of importance:
Cell count first → this diagnoses SBP

Step 7 – Remove needle and dress

Remove smoothly
Apply pressure
Apply dressing
Document clearly

Procedure takes 5–10 minutes.

✅ How to interpret results (clinically important)

SBP diagnosis:

👉 Neutrophils ≥ 250/mm³

= Treat immediately

Do not wait for culture.

Start:

IV antibiotics
Albumin
Escalate

SAAG (if checking cause):

Serum albumin – Ascitic albumin

≥11 → portal hypertension
<11 → malignancy/infection/other

But on-call, SBP rule-out is the priority.

🚨 When to escalate after the tap

Escalate if:

Bloody tap
Persistent leak
Severe pain
Hypotension
SBP confirmed
Patient deteriorates

❌ Common mistakes juniors make

Not tapping when indicated
Waiting for ultrasound
Sending wrong bottles
Forgetting culture bottles
Not sending cell count
Contaminating sample
Poor documentation

Most harm comes from not doing the tap, not from doing it.

✅ Take-home concept

Ascitic tap is low risk and high yield.
If a cirrhotic patient is unwell, tap early — it can save their life.