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Three Part Question

In [patients with abdominal pain] does [a normal serum amylase] exclude [the diagnosis of pancreatitis]

Clinical Scenario

A 44 year old man presents to the emergency department with a four hour history of severe epigastric pain. You consider a diagnosis of pancreatitis and organise a serum amylase to be taken. You wonder if a single normal serum amylase result is sufficiently sensitive to rule out pancreatitis in this patient.

Search Strategy

Medline 1966–07/03, Embase 1980-07/03 using the Ovid interface.
[(exp Abdominal pain/ OR abdominal pain.mp OR exp Pancreatitis/ OR pancreatitis, acute necrotising/ OR pancreatitis, alcoholic/ OR pancreatitis.mp) AND (exp Amylases OR amylase$ OR amylase.mp) AND (exp SENSITIVITY AND SPECIFICITY OR (sensitivity.mp AND specificity.mp)] LIMIT to human AND English.

Search Outcome

Altogether 191 papers found of which 4 papers were relevant to the original question.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Steinberg WM et al, 1985, USA	39 patients with pancreatitis were compared with 127 controls with abdominal pain	Diagnostic Study	Sensitivity and specificity of two amylase serum assays for pancreatitis. Using upper limit of normal	Amylase 1 = sensitivity 94.9% specificity 88.9%. Amylase 2 = sensitivity 94.9% specificity 86.0%	Various techniques used to confirm diagnosis including CT scans, laparotomy, USS scans Patients referred to gastroenterology team with diagnosis based on serum amylase result, thus spectrum bias
			Using best cut off	Amylase 1 = sensitivity 94.8% specificity 98.4% Amylase 2 = sensitivity 92.3% specificity 100%
Lin XZ et al, 1989, Taiwan	62 consecutive patients with image-proven pancreatitits, and 414 patients with an acute abdomen	Diagnostic Study	Sensitivity and specificity of serum amylase at selected cut-off 3 times above upper limit of normal	Sensitivity of serum amylase: 84% in image proven pancreatitis, 92% in patients with or without image verified disease	Problems with gold standard diagnosis of pancreatitis Serum amylase used in diagnosis. (incooperation bias) Various gold standards used within the study
Clavien PA et al, 1989, Canada	352 consecutive attacks of acute pancreatitis in 318 patients	Diagnostic study	Sensitivity and specificity of serum amylase (<160IU/l) compared to gold standards of CT or laparotomy	Sensitivity of 81% at presentation	Chronic pancreatitis patients were excluded
Winslet M et al, 1992, UK	417 patients with acute pancreatitis	Diagnostic Study	Sensitivity of serum amylase (>1000IU) for detecting acute pancreatitis at hospital admission	Mild cases 96.1%. Severe cases 87.4%. Alcohol subgroup 86%	Variable gold standards used Not all patients had CT
			Sensitivity of serum amylase (>1000IU) for detecting acute pancreatitis at 48 hours	Mild cases 33.3% Severe cases 48.2%. Alcohol subgroup 76%

Comment(s)

The gold standard for the diagnosis of pancreatitis is considered to be surgical examination at laparotomy or pancreatic histology. Often in practice such information is either unavailable or obtained at post-mortem. In the absence of a readily available gold standard it becomes necessary to evaluate serum diagnostic markers against radiological methods such as CT scanning. Only two studies used an independent 'gold standard' for all patients to compare the diagnostic test under consideration. Despite this weakness all the above studies except one reported sensitivities below 95%, especially in alcohol-related pancreatitis cases.

Clinical Bottom Line

In patients presenting to the emergency department with acute abdominal pain a normal serum amylase concentration is not sufficiently sensitive to rule out the diagnosis of acute pancreatitis.

Level of Evidence

Level 2 - Studies considered were neither 1 or 3.

References

1. Steinberg WM, Goldstein SS, Davis ND, et al. Diagnostic assays in Acute Pancreatitis. Ann Intern Med 1985;102(5):576-580.
2. Lin XZ, Wang SS, Tsai YT, et al. Serum amylase, isoamylase, and lipase in the acute abdomen. Their diagnostic value for acute pancreatitis. J Clin Gastroenterol 1989;11(1):47-52.
3. Clavien PA, Robert J, Meyer P, et al. Acute pancreatitis and normoamylasemia. Not an uncommon combination. Ann Surg 1989;210(5):614-20.
4. Winslet M, Hall C, London NJ, et al. Relation of diagnostic serum amylase levels to aetiology and severity of acute pancreatitis Gut 1992;33(7):982-6.