01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Acute pancreatitis is an inflammatory pancreatic injury whose initial presentation ranges from a painful but self-limiting illness to rapidly evolving organ dysfunction. Acinar injury and local inflammatory signalling can be followed by oedema, necrosis and a systemic response. The diagnosis describes the acute syndrome; it does not identify its cause, establish infection or assign final severity. Those are separate clinical questions, and a safe assessment answers each in turn while treating immediate physiological disturbance.
The familiar presentation is persistent epigastric pain, often radiating towards the back, with nausea and vomiting. Neither radiation nor every classical feature is essential. Two concordant diagnostic criteria are sufficient, but enzyme elevation has competing explanations and imaging can be unrevealing very early. Interpret the result against onset, examination and the other findings. In a patient with an atypical abdomen, the useful question is whether pancreatitis accounts for the illness, rather than whether a lipase result happens to cross a numerical threshold.
Key points
- Diagnose using two of three: characteristic pain, pancreatic enzymes above three times the laboratory upper limit, or compatible imaging.
- When typical pain and a diagnostic enzyme rise agree, CT is not required merely to provide the third criterion.
- Establish the cause with a focused history, liver tests, calcium, triglycerides and biliary ultrasound; alcohol exposure alone is insufficient attribution.
- A very high lipase confirms neither organ failure nor pancreatic necrosis; follow physiology and organ function separately.
- Use early cross-sectional imaging for uncertainty or another urgent diagnosis; routine necrosis assessment is more informative after about 72–96 hours from onset.
- Unexplained or recurrent pancreatitis needs a documented investigation plan, often repeat ultrasound followed by EUS and, if unrevealing, MRI/MRCP.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Biliary and alcohol-associated injury
Transient ampullary obstruction by a stone and alcohol-associated pancreatic injury are common causal categories. Their clinical assessment differs: documented gallstones, liver-test patterns and a careful alcohol history must be interpreted together rather than replacing investigation with an assumption.
Other and unexplained causes
Hypertriglyceridaemia, hypercalcaemia, selected medicines, ERCP, trauma, autoimmune disease and structural or inherited susceptibility can contribute. Recurrent or unexplained attacks need a planned specialist investigation, including consideration of a tumour where the presentation or age raises concern.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Acinar injury
Disruption of normal acinar function initiates pancreatic inflammation and local tissue injury. The clinical syndrome reflects both pancreatic damage and the response of surrounding tissues; the amount of circulating enzyme is not a direct measurement of damage severity.
- 2Local inflammatory change
Oedema can resolve as the episode settles, whereas more substantial tissue injury can produce pancreatic or peripancreatic necrosis. The nature and evolution of a collection depend on its contents and timing, not simply the appearance of fluid early in the illness.
- 3Systemic consequences
Inflammatory signalling, vascular permeability and fluid redistribution may impair circulation and distant organs. Respiratory and renal dysfunction therefore require their own assessment even when the patient initially presents chiefly with abdominal pain and vomiting.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Clarify onset, persistence, location, radiation, vomiting and previous similar episodes. Ask about biliary colic, recent procedures, abdominal trauma and medications as well as alcohol. Examine perfusion, hydration, respiration and abdominal tenderness together: pain intensity by itself cannot classify severity. A patient who looks progressively unwell needs repeated assessment even if the first set of observations was reassuring.
Sudden maximal pain, a rigid abdomen, marked gastrointestinal bleeding or pain disproportionate to physical findings should reopen the differential. Pancreatic enzymes can rise in other intra-abdominal disease and with impaired renal clearance. Do not allow an abnormal blood test to delay investigation for perforation, intestinal ischaemia or a vascular catastrophe when the clinical pattern points there.
Jaundice, a history of postprandial right upper quadrant pain, gallstones and an early alanine aminotransferase rise support a biliary cause. These clues are cumulative rather than individually mandatory. A passed stone may leave no persisting duct obstruction. Fever, systemic illness and obstructive jaundice raise a different immediate issue: possible cholangitis requiring urgent biliary assessment.
Review the timing of new or changed medicines, triglyceride and calcium abnormalities, previous ERCP, family history and recurrent unexplained attacks. Ask about alcohol sensitively and quantify the pattern rather than labelling the disease from any reported intake. More than one factor can coexist; recurrent episodes despite addressing an apparent cause deserve a fresh causal review.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Lipase with clinical assessmentFirst step - Why
- Test whether the biochemical and clinical criteria agree at this presentation.
- Interpretation and limitations
- Characteristic persistent upper abdominal pain plus lipase above three times the laboratory upper limit establishes two criteria, so confirmatory CT is unnecessary solely for diagnosis. Amylase is an alternative where used. An isolated elevation is not enough; a low or modest value with a late or otherwise convincing presentation may require imaging and reconsideration of timing or another diagnosis.
- 02
Aetiological blood tests and ultrasound - Why
- Look for a remediable cause during the initial admission.
- Interpretation and limitations
- Request liver tests, calcium and triglycerides alongside the basic physiological blood assessment, and assess gallbladder and bile ducts with ultrasound. Raised ALT early in the attack supports gallstone disease but does not prove an obstructed duct. Poor visualisation or a normal initial ultrasound does not exclude a small passed stone or microlithiasis.
- 03
Contrast CT when the question warrants it - Why
- Resolve diagnostic uncertainty, deterioration or a suspected complication.
- Interpretation and limitations
- An early scan is appropriate when another urgent abdominal diagnosis must be excluded or the diagnosis remains uncertain. For routine assessment of necrosis and extent, CT after approximately 72–96 hours from symptom onset is more informative than an automatic admission scan. Renal function, contrast risks and the clinical question influence the chosen modality and timing.
- 04
Repeated physiology and organ-function tests - Why
- Separate the diagnosis from evolving consequences of the attack.
- Interpretation and limitations
- Trend observations, oxygen requirement, urine output, urea, creatinine, haematocrit and electrolytes as clinically indicated. A falling enzyme concentration does not establish recovery or justify ignoring new organ dysfunction. A patient may have substantial pancreatic injury without a proportionately greater serum enzyme value; serial lipase is not a severity-monitoring strategy.
- 05
EUS and MRI/MRCP after an unexplained attack - Why
- Investigate causes that initial history, blood tests and ultrasound have not established.
- Interpretation and limitations
- Arrange repeat transabdominal ultrasound after recovery when the first examination was unrevealing; EUS is the next investigation after a negative initial evaluation and repeat ultrasound, with MRI/MRCP if EUS is negative. EUS can detect microlithiasis and small lesions; MRCP clarifies duct anatomy. In unexplained pancreatitis after age 50, assess specifically for a pancreatic tumour with appropriate imaging or EUS.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Perforation or intestinal ischaemia
Peritonism, abrupt severe pain or pain disproportionate to examination requires urgent assessment for another abdominal emergency. A coincidental or secondary enzyme rise does not exclude these diagnoses, and the need for urgent imaging overrides routine pancreatitis imaging timing.
Biliary disease without pancreatitis
Cholecystitis, biliary colic and cholangitis can cause upper abdominal symptoms. Use the full pancreatic diagnostic criteria and assess for coexistence: cholangitis changes the urgency of biliary intervention even when pancreatitis is also present.
Vascular or cardiac pain
Aortic disease and myocardial ischaemia can present with epigastric pain, particularly in a patient with relevant risk or haemodynamic disturbance. Examination, ECG and targeted investigation should follow the clinical suspicion rather than the pancreatic enzyme result alone.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Worked caseTwo criteria, then a causeFirst stepA constructed example links diagnostic certainty to an observed inpatient decision.+
- 1A 44-year-old woman presents with 12 hours of persistent epigastric pain radiating to the back and vomiting. Lipase is 920 U/L against an upper limit of 60 U/L; examination shows epigastric tenderness without rigidity. The team diagnoses pancreatitis from pain and enzymes, starts supportive care and does not order CT simply to obtain a third criterion.
- 2Her ALT is 260 U/L and ultrasound shows gallbladder stones without duct dilatation. Bilirubin falls during observation; she has no fever, persistent jaundice or evidence of cholangitis. These findings support a biliary attack after stone passage. The surgical team records this causal assessment and the absence of an immediate indication for ERCP. She subsequently recovers without organ failure and undergoes uncomplicated cholecystectomy during the same admission.
- 3Over the next day her pulse settles, urine output remains adequate, oxygen is not required and oral intake resumes. The team reassesses severity rather than using the lipase magnitude as a prediction. With a mild clinical course and no local complication identified, the biliary service performs laparoscopic cholecystectomy on day three without an observed perioperative complication.
- 4At the discharge review she is eating, mobilising and comfortable on the agreed oral analgesic plan. The record identifies gallstones as the working cause and specifies return for recurrent pain, fever, jaundice or inability to drink. The observed improvement supports the course of this episode; it does not imply that untreated gallstones could be ignored.
02Initial assessmentConfirm without diagnostic anchoringUse when acute upper abdominal pain and a raised pancreatic enzyme first appear.+
- 1Assess circulation, breathing, mental state and the abdomen before treating the laboratory label as the whole diagnosis. Obtain a focused history and appropriate blood tests, establish symptom onset and consider immediately dangerous alternatives in parallel.
- 2Apply the two-of-three framework using the actual laboratory upper limit. If pain and enzymes are concordant, begin pancreatitis care without waiting for a routine CT; if they are discordant, choose imaging to answer the unresolved question rather than repeating tests reflexively.
- 3EscalationDocument a provisional cause and the evidence behind it. Arrange biliary ultrasound and the relevant metabolic tests during the admission. Escalate possible cholangitis, persistent obstruction or physiological deterioration through the appropriate urgent pathway.
03Unexplained diseaseFinish the causal investigationUse after an attack remains unexplained by initial clinical, biochemical and biliary assessment.+
- 1Revisit the medication timeline, alcohol history, triglycerides, calcium, previous instrumentation and family history. Confirm that the initial ultrasound was adequate and arrange a repeat examination after recovery if it was negative or limited.
- 2After the negative initial workup and repeat ultrasound, seek EUS; use MRI/MRCP if EUS is unrevealing or to resolve a specific ductal question. A mass concern or unexplained episode in an older adult warrants deliberate cancer assessment rather than an indefinite idiopathic label.
- 3For recurrent unexplained attacks, discuss specialist review and selected genetic investigation with counselling. Record who will check the results and revise the causal diagnosis. Finding a duct variant alone does not establish that it caused every attack.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Early organ dysfunction
Circulatory, respiratory and renal compromise may emerge quickly and require immediate escalation. The later distinction between transient and persistent organ failure is a classification of the observed course, not permission to delay support.
Necrosis and collections
Pancreatic or peripancreatic injury can develop into necrosis or evolving collections. New fever or deterioration needs assessment, but early inflammation is often sterile and an elevated inflammatory marker alone does not establish infected necrosis.
Recurrence and lasting impairment
Failure to address a remediable cause exposes the patient to further attacks. Some patients develop continuing nutritional, exocrine or endocrine problems, particularly after more extensive disease; recovery review should respond to persistent symptoms rather than stopping at pain resolution.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- During the first admission, reassess pain alongside respiratory rate, oxygen need, pulse, pressure, mental state and urine output. A new abnormal trend changes disposition even if the biochemical diagnosis was straightforward and the original observations were stable.
- Check the evolution of liver tests when a biliary cause is suspected. Persistent jaundice, fever or evidence of obstruction requires renewed biliary review; a spontaneously falling bilirubin is relevant but does not remove the need for definitive recurrence prevention.
- Review the cause before discharge and list unresolved investigations with a responsible service and timeframe. A normal admission ultrasound should not quietly close the workup of an otherwise unexplained attack.
- Explain return symptoms and ensure the patient can take sufficient oral fluid and nutrition. Recurrent pain, vomiting, jaundice, fever or increasing breathlessness should prompt reassessment rather than waiting for an outpatient investigation.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Aetiology changes prevention
Confirming pancreatitis is only the beginning of causal reasoning. A biliary episode prompts assessment for definitive gallstone treatment; a metabolic or medication-associated attack prompts a different prevention plan. Where a drug is suspected, balance chronology, alternative causes and the consequences of stopping it with the relevant prescriber rather than asserting causation from a list of reported associations.
A normal duct is not exculpatory
Gallstones can trigger an episode and then pass. Absence of duct dilatation or a retained stone does not erase a convincing biliary history, transient liver-test abnormality and gallbladder stones. Conversely, incidental gallstones do not explain every atypical episode; the clinical, biochemical and imaging evidence must remain coherent.
Imaging has a timed purpose
Early CT and later CT answer different questions. The first may exclude another urgent diagnosis; the later may define necrosis or support intervention planning. A normal-looking or oedematous pancreas very early in the illness cannot guarantee that complications will not evolve. Order a repeat study for a new clinical question, not because a calendar interval has elapsed.
Do not overlook a small tumour
An unexplained attack can precede recognition of an obstructing pancreatic lesion. This matters particularly after age 50 or with other concerning features. Arrange appropriate cross-sectional imaging and/or EUS, and make follow-up ownership explicit. Symptomatic recovery from pancreatitis is compatible with an underlying lesion remaining present.
11Common pitfallsFrequent interpretation and management errors.
- 01
Calling an isolated raised lipase diagnostic when the clinical presentation is discordant; reassess alternative abdominal and systemic explanations before closing the diagnosis.
- 02
Requesting admission CT solely because all three diagnostic criteria seem necessary; two concordant criteria are sufficient, while imaging remains available for a different urgent question.
- 03
Assigning alcohol as the cause because a patient reports drinking, without checking gallstones, metabolic abnormalities, medications and the temporal history.
- 04
Using serial enzymes as a substitute for urine output, oxygen requirement and organ-function trends; biochemical decline does not establish physiological safety.