Acute pancreatitis — severity and complication assessment

ACR AC Acute Pancreatitis (2019); revised Atlanta classification (Gut 2013); IAP/APA 2013; ACG 2024

A card mostly about timing. The diagnosis is biochemical, so imaging is asked to grade necrosis and find collections — and both take days to declare themselves, which makes a day-one CT the commonest avoidable study in this disease.

Established acute pancreatitis, either failing to settle, deteriorating clinically, or being assessed for complications before intervention.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Haemodynamic state

The fact that lets a pathway waive its own requirements. A crashing patient does not wait for a score.

Time since onset

Decides thrombolysis and thrombectomy windows, testicular salvage, and whether an ischaemic limb is still salvageable.

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

CT Abdomen and Pelvis — Portal Venous Phase

CT Abdomen and Pelvis

What we'd amend, and why

Necrosis is diagnosed as absent parenchymal enhancement, so this is a perfusion measurement rather than a morphological one, and it requires intravenous contrast and a well-timed venous acquisition. It also requires time: microcirculatory failure evolves over the first days, so scanning before roughly 48 to 72 hours from symptom onset systematically understates the extent of necrosis in a patient with an otherwise unequivocal presentation, and the interval most guidelines describe as optimal for grading is closer to 72 to 96 hours from the onset of pain rather than from admission. Two exceptions are explicit and neither is a softening of the rule: diagnostic uncertainty, where the scan exists to exclude a perforation or mesenteric ischaemia, and clinical deterioration or suspected haemorrhage, where it exists to find a complication. Outside those, an early scan buys nothing and will be repeated. The same acquisition maps peripancreatic collections and shows the vascular complications — splenic vein thrombosis, pseudoaneurysm — that change management, and collections are named against the revised Atlanta definitions, which are defined by time from onset as well as by content.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayadult — Adults
rulerule-contrast-reaction-premed — Prior contrast reaction and elective premedication; checked by Nurse before the scan
rulerule-metformin — Metformin and iodinated contrast; checked by Radiographer at the scanner
rulerule-paeds-dose — Child-sized technique and contrast dose; checked by Radiographer at the scanner
rulerule-pregnancy-ionising — Pregnancy status before an ionising exposure; checked by Radiographer at the scanner
rulerule-renal-iodinated — Kidney function and intravenous iodinated contrast; checked by Radiographer at the scanner
rulerule-iv-access — Intravenous access adequate for the planned injection; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(4)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

Metformin and iodinated contrast
Confirm whether the patient takes metformin or a metformin-containing combination, and if so whether ACR Category II applies (eGFR below 30, known or suspected AKI, or an arterial catheter study likely to cause renal embolisation). If Category I — that is, no AKI and eGFR at or above 30 — no action of any kind is needed.
Radiographer at the scannerAt the scanner
Flags back if: The patient takes metformin AND meets ACR Category II — eGFR below 30 mL/min/1.73 m2, known or suspected acute kidney injury, or an arterial catheter procedure with likely renal arterial embolisation. Metformin plus a normal or mildly reduced eGFR is explicitly NOT a flag-back: there is no need to stop metformin before or after intravenous iodinated contrast in Category I patients, and no need to re-check creatinine afterwards.
Child-sized technique and contrast dose
Confirm that a size- or weight-based protocol is selected — child-sized kV and mAs against size-based diagnostic reference ranges — and that contrast volume is calculated by weight rather than taken from an adult default. Weight-based iodinated contrast volumes of roughly 1.5–2.0 mL/kg are widely used in paediatric CT.
Radiographer at the scannerAt the scanner
Flags back if: No paediatric or size-based protocol exists on the scanner for the requested examination, or the requested coverage or number of phases exceeds what the clinical question needs — for example a multiphase study where a single phase answers it, or whole-body coverage for a focal question.
Pregnancy status before an ionising exposure
Make the pregnancy enquiry immediately before the exposure and record the answer. In the UK this is a statutory operator duty discharged at the time of exposure under the employer’s written procedures required by IR(ME)R 2017 — it is not something the vetting radiologist can perform or pre-empt, and a request is complete without it.
Radiographer at the scannerAt the scanner
Flags back if: The patient states that she is, or may be, pregnant AND the uterus is in or near the primary beam. The exposure is then paused for re-justification by the IR(ME)R practitioner before it proceeds.
Intravenous access adequate for the planned injection
Site and test a cannula that supports the protocol flow rate, preferring an antecubital or large forearm vein, and observe the injection for extravasation. A 20-gauge or larger cannula is preferred for flow rates of 3 mL/s or more.
Radiographer at the scannerAt the scanner
Flags back if: No cannula can be sited that supports the protocol flow rate — for example only a 22-gauge hand or foot cannula for a CT angiogram needing 4–5 mL/s; or the only available access is a central line or port that is not labelled power-injectable; or an extravasation occurs.

Worth asking the referrer (1)

None of these hold the request up. They sharpen the protocol or the plan that follows.

How many days ago did the pain begin?
The interval from onset, not the date of admission, determines whether a contrast-enhanced CT can grade necrosis at all.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Haemodynamically unstable or deteriorating — scan now, whatever the interval

Role	Study & protocol	Why this answers the question
First line	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase usually appropriate	The 48 to 72 hour rule is about grading necrosis, and grading necrosis is not what this patient needs. Shock in acute pancreatitis raises three questions that all have to be answered now: is the diagnosis right at all — a perforated ulcer and acute mesenteric ischaemia both raise amylase and both kill faster than pancreatitis does; is there haemorrhage, from a splenic or gastroduodenal artery pseudoaneurysm eroded by pancreatic enzymes, which is an embolisation problem measured in minutes; and is there a vascular complication such as splenic or portal venous thrombosis. A portal-venous acquisition answers all three. What must travel with the report is the timing caveat rather than a false negative: if the scan is early, the extent of necrosis on it is a floor and not a measurement, and it should be described as not yet assessable rather than as absent. Guidelines name diagnostic uncertainty and clinical deterioration as the two accepted indications for early CT, and this arm is those two.
Second line	Ultrasound abdomen Ultrasound abdomen — full survey	The aetiology still has to be established, and in the unstable patient it can be done at the bedside without moving anybody: gallstones, duct calibre and free fluid in one short study. It matters here more than usual, because a shocked jaundiced patient with gallstone pancreatitis and cholangitis needs urgent endoscopic duct clearance rather than more imaging, and that decision is made on the ultrasound and the bilirubin, not on the CT.

Nothing here contradicts the timing argument. It says that the timing argument answers a question about necrosis, and this patient is being scanned for a different question.
A CT performed early because the patient deteriorated will usually need repeating once the disease has declared itself; say so in the report rather than letting the early study stand as the severity assessment.

Within roughly 48 hours of symptom onset

Role	Study & protocol	Why this answers the question
First line	Ultrasound abdomen Ultrasound abdomen — full survey usually appropriate	In the first two days there is exactly one imaging question whose answer changes what happens to this patient, and it is the cause. Gallstones are the commonest aetiology, ultrasound is the test that finds them and the dilated duct that goes with them, and a stone commits the patient to cholecystectomy on this admission or to endoscopic clearance if there is coexisting cholangitis. The diagnosis of pancreatitis itself is already made on pain plus enzymes and does not need a scan to confirm it.
Second line	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase usually not appropriate	Necrosis is absent enhancement, and absent enhancement requires the microcirculation to have failed — a process that evolves over the first two to three days. A contrast-enhanced CT taken before that has happened does not find early necrosis, it finds a pancreas that has not yet declared itself, and it reads as reassurance in a patient who will go on to have extensive necrosis and will need the scan repeating. Systematic understaging is the specific error, not simply a wasted study. Two exceptions are genuine and both are different questions rather than exceptions to this reasoning: where the diagnosis of pancreatitis is itself in doubt and a perforation or mesenteric ischaemia has to be excluded, and where a patient deteriorates abruptly with suspected haemorrhage — those need a scan now and are served by their own cards. Deterioration that is simply the expected early systemic inflammatory response is not one of them.
Problem solving	MRCP (MR Cholangiopancreatography) MRCP — standard unenhanced	Where the ultrasound is equivocal or the liver function tests suggest a retained duct stone, cholangiography answers the aetiological question directly and with no radiation, and it does so on day one as well as it does on day ten because it is not measuring perfusion. This is the right escalation in the first 48 hours, rather than bringing the CT forward.

The interval that matters is from the onset of pain, not from admission — a patient admitted this morning may be four days into the illness.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase usually appropriate	Necrosis is diagnosed as absent parenchymal enhancement, so this is a perfusion measurement rather than a morphological one, and it requires intravenous contrast and a well-timed venous acquisition. It also requires time: microcirculatory failure evolves over the first days, so scanning before roughly 48 to 72 hours from symptom onset systematically understates the extent of necrosis in a patient with an otherwise unequivocal presentation, and the interval most guidelines describe as optimal for grading is closer to 72 to 96 hours from the onset of pain rather than from admission. Two exceptions are explicit and neither is a softening of the rule: diagnostic uncertainty, where the scan exists to exclude a perforation or mesenteric ischaemia, and clinical deterioration or suspected haemorrhage, where it exists to find a complication. Outside those, an early scan buys nothing and will be repeated. The same acquisition maps peripancreatic collections and shows the vascular complications — splenic vein thrombosis, pseudoaneurysm — that change management, and collections are named against the revised Atlanta definitions, which are defined by time from onset as well as by content.
First line	Ultrasound abdomen Ultrasound abdomen — full survey usually appropriate	Every episode needs its cause established, and ultrasound is what finds gallstones and biliary dilatation. Guidelines ask for it in every patient with acute pancreatitis, on admission, not as a substitute for the severity scan but alongside it — because a stone commits the patient to cholecystectomy on this admission and, if the ducts are obstructed and the patient is septic, to endoscopic clearance within hours. It is also the only rung on this ladder that changes anything in the first two days, when CT cannot yet grade necrosis. Accepting a request that asks for it is therefore correct, whatever the CT is or is not doing.
Problem solving	MRCP (MR Cholangiopancreatography) MRCP — standard unenhanced	Heavily T2-weighted cholangiography shows a retained duct stone that ultrasound missed and demonstrates duct disruption, and its fluid sensitivity distinguishes a collection with solid necrotic debris from simple fluid better than CT does — a distinction that decides whether percutaneous drainage will succeed.

Pitfalls

Accepting a day-one CT in a patient with typical pain and high enzymes. It rarely changes management and reliably understates necrosis.
Reporting an early scan as showing no necrosis. Before the microcirculation has failed there is nothing to see, so an early study measures the floor of the disease and not its extent; the phrase the report needs is "too early to grade", and a clean early CT must never be used to step a patient down.
Reading the timing rule as a prohibition. Diagnostic uncertainty and clinical deterioration are accepted indications for scanning now, and a shocked patient with suspected haemorrhage, a pseudoaneurysm, a perforation or mesenteric ischaemia is scanned on the day whatever the interval says.
Reporting non-enhancement as necrosis on a mistimed or low-contrast-volume study, which overstates severity in the opposite direction.
Repeating CT every few days without a stated question. Deterioration, planned intervention or suspected bleeding are questions; routine surveillance is not.
Calling every peripancreatic collection a pseudocyst. Under the revised Atlanta definitions the name depends on both the interval — roughly four weeks — and whether the collection contains necrotic debris, and using the wrong name sends the patient down the wrong drainage pathway.
Forgetting the aetiology entirely because the request only asked about severity. Every patient needs the gallstone question answered, and gallstone pancreatitis with jaundice, fever and rigors is cholangitis — a duct-drainage emergency that belongs on the obstructive jaundice pathway, not a reason for another scan.

Priors — what to pull first

Compare with the earliest scan of the episode: the useful information is how collections and necrosis are evolving, not their appearance on any single day.
Check whether a previous episode has already established the aetiology; repeating the aetiological work-up wastes the admission.

What makes a good request

Acute pancreatitis is diagnosed on pain plus enzyme elevation; CT is not needed to make the diagnosis when the presentation is typical.
Necrosis needs time and perfusion failure to become visible, so a scan performed too early can be falsely reassuring and will usually be repeated. The interval runs from the onset of pain, and grading is most reliable from around 72 to 96 hours.
The two accepted reasons to scan earlier than that are diagnostic uncertainty and clinical deterioration — including suspected haemorrhage or a pseudoaneurysm. Say which one applies and the scan stops being an early scan and becomes a different examination.
Every patient still needs the aetiology answered, and gallstones are the commonest answer — that is an ultrasound question, not a CT one, and it should be asked of every patient rather than only of the ones whose CT was unhelpful.
Severity is graded against the revised Atlanta classification: interstitial oedematous against necrotising disease, and collections named by whether they contain necrosis and by whether four weeks have passed.

Scoring this once it is done

The classification and risk tools this question ends in.

Pancreatic Collections Nomenclature & Modified CT Severity Index Ranson Criteria for Acute Pancreatitis Severity eGFR (CKD-EPI 2021 Creatinine)

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

CT Abdomen and Pelvis — Portal Venous Phase Ultrasound abdomen — full survey MRCP — standard unenhanced

Confirm locally

CT Abdomen and Pelvis — Portal Venous Phase: timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.