Macroamylasaemia: how common is it?

Significant elevations of serum amylase caused by macroamylase: Case reports and detection possibilities

BACKGROUND

The presence of isolated elevated serum amylase levels can be caused by high molecular mass complexes. We describe 13 cases of hyperamylasemia detected in adult patients without clinical symptoms of a pancreatic disorder. Five of them were thoroughly examined using different tools for the detection of macrocomplexes.

METHODS

We performed both screening and more advanced methods of macroamylase detection, including polyethylene glycol precipitation, sample storage at 4°C and separation by gel filtration.

RESULTS

The presence of macroamylase in the suspected samples was confirmed by the methods described, except for the sample storage at 4°C. In this method, the enzyme activity did not decrease. The polyethylene glycol precipitation activity (% PPA) averaged 89.1% for amylase, whereas the control samples averaged 30.7%. Gel filtration chromatography confirmed an IgA macroamylase peak in three samples and an IgG macroamylase peak in two samples.

CONCLUSION

The presence of macroamylase should be suspected whenever the clinical history and condition of the patient do not match the measured enzyme value to avoid diagnostic errors and unnecessary invasive examinations. The presence of macrocomplexes is considered a benign process that may occur in apparently healthy individuals. Cooperation between clinicians and laboratory staff is necessary.

A multidisciplinary approach to an unusual cause of hyperamylasaemia

Clinical features together with elevation of pancreatic enzymes are the key diagnostic indicators of acute pancreatitis. We report a case of a woman in her 50s who presented with abdominal distension and serum amylase raised to more than 30 times the upper limit of normal. She was initially treated for acute pancreatitis, however, she was not symptomatic of this and the pancreas appeared to be normal on CT scan. Further investigations revealed the patient had a high-grade serous ovarian carcinoma with nodal metastatic spread. An amylase-secreting ovarian tumour was suspected, which was supported by elevated salivary-amylase isoenzymes, consistent with previous reports in the literature. The patient was treated with chemotherapy and surgery, during which her serum amylase and CA-125 initially fell significantly, but eventually both increased, reflecting disease progression. This case serves as an important reminder to consider non-pancreatic causes of raised serum amylase, to avoid misdiagnosis.

Elevated serum amylase in patients with chronic pancreatitis: acute attack or macroamylasemia?

BACKGROUND AND AIM

Asymptomatic patients with chronic pancreatitis not infrequently have elevated concentrations of amylase, even though detailed examination reveals no indication of an acute exacerbation.

METHODS

One hundred and eighty-six consecutive patients with chronic pancreatitis were examined clinically and, if indicated, by ultrasonography and computed tomography. In addition, all patients underwent determination of serum amylase and serum lipase as well as amylase/creatinine clearance, followed as required by a polyethylene glycol test and/or chromatography to demonstrate macroamylase.

RESULTS

Twenty (11%) of the 186 patients had macroamylasemia, and 15 of these 20 had hyperamylasemia. In the remaining five cases the serum amylase levels were within the normal range.

CONCLUSIONS

Patients with asymptomatic chronic pancreatitis and hyperamylasemia should first be investigated for macroamylasemia, before initiating any costly or complex procedures in the attempt to demonstrate a clinically silent or only mildly symptomatic attack of their disease.

Acute pancreatitis

Acute pancreatitis (AP) is an important cause of morbidity and mortality worldwide and the annual incidence appears to be increasing. It presents as a mild self-limiting illness in 80% of patients. However, one-fifth of these develop a severe complicated life-threatening disease requiring intensive and prolonged therapeutic intervention. Alcohol and gallstone disease remain the commonest causes of AP but metabolic abnormalities, obesity and genetic susceptibility are thought be increasingly important aetiological factors. The prompt diagnosis of AP and stratification of disease severity is essential in directing rapid delivery of appropriate therapeutic measures. In this review, the range of diagnostic and prognostic assays, severity scoring systems and radiological investigations used in current clinical practice are described, highlighting their strengths and weaknesses. Increased understanding of the complex pathophysiology of AP has generated an array of new potential diagnostic assays and these are discussed. The multidisciplinary approach to management of severe pancreatitis is outlined, including areas of controversy and novel treatments.

Clinical laboratory assessment of acute pancreatitis

BACKGROUND

Several biochemical markers in blood and urine have been investigated to establish their clinical application in patients with acute pancreatitis (AP). The relevant studies are reviewed and critically appraised.

METHODS

Medline and the World Wide Web were searched and the relevant literature was classified under the following categories: (1) diagnosis of AP and (2) prediction of: a) disease severity, b) pancreatic necrosis and its secondary infection, c) organ failure and death, and d) disease etiology.

RESULTS AND CONCLUSIONS

Serum lipase is a more reliable diagnostic marker of AP than serum amylase. Urinary strip tests for trypsinogen activation peptide (TAP) and trypsinogen-2 provide a reliable early diagnosis of AP. Useful predictors of severity may include serum procalcitonin and urinary TAP and trypsinogen-2 on admission, serum interleukins-6 and -8 and polymorphonuclear elastase at 24 h, and serum C-reactive protein (CRP) at 48 h. Other markers such as amyloid A and carboxypeptidase B activation peptide (CAPAP) need further investigation. Biochemical prediction of pancreatic necrosis requires 72 h to reach reliability and is impractical. However, the daily monitoring of serum procalcitonin provides a non-invasive detection of infected necrosis; the promising role of phospholipase A(2) in this regard requires further investigation. Early transient hypertransaminasemia reliably predicts biliary etiology, while serum carbohydrate-deficient transferrin and trypsin may predict an alcoholic etiology.

A critical evaluation of laboratory tests in acute pancreatitis

An ideal laboratory test in the evaluation of a patient with acute pancreatitis (AP) should, in addition to accurately establishing the diagnosis of AP, provide early assessment of its severity and identify the etiology. None of the tests available today meet all these criteria, and presently there is no biochemical test that can be considered the "gold standard" for the diagnosis and assessment of severity of AP. In the diagnosis of AP, serum amylase and lipase remain important tests. Advantages of amylase estimation are its technical simplicity, easy availability, and high sensitivity. However, its greatest disadvantage is its low specificity. A normal amylase would usually exclude the diagnosis of AP, with the exception of AP secondary to hyperlipidemia, acute exacerbation of chronic pancreatitis, and when the estimation of amylase is delayed in the course of the disease. The major advantage of lipase is an increased sensitivity in acute alcoholic pancreatitis and in patients who initially present to the emergency room days after the onset of the disease, as lipase remains elevated longer than amylase. Although once considered to be specific for AP, nonspecific elevations of lipase have been reported in almost as many disorders as amylase, thus decreasing its specificity. Simultaneous estimation of amylase and lipase does not improve the accuracy. Other enzymes for the diagnosis of AP--pancreatic isoamylase, immunoreactive trypsin, and elastase--are more cumbersome and expensive and have no clear role in the diagnosis of AP. No enzyme assay has a predictive role in determining the severity or etiology of AP. Once the diagnosis of AP is established, daily measurements of enzymes have no value in assessing the clinical progress of the patient or ultimate prognosis and should be discouraged. A host of new serological and urinary markers have been investigated in the last few years. Their main use is in predicting the severity of AP. At present, serum C-reactive protein at 48 h is the best available laboratory marker of severity. Urinary trypsinogen activation peptides within 12-24 h of onset of AP are able to predict the severity but are not widely available. Serum interleukins 6 and 8 seem promising but remain experimental.

Electrophoretic analysis of enzyme-linked immunoglobulins and their clinical significance

The appearance of circulating enzyme-linked immunoglobulin complexes (E-Ig) is common for most enzymes used in clinical biochemical tests. The presence of E-Ig may result in altered enzyme activity in serum and interfere with the measurement of isoenzymes, and is thus of diagnostic importance. E-Ig can be identified by confirming that the binding protein is an immunoglobulin by its reaction with specific anti-human immunoglobulin antibodies. Currently, the presence of E-Ig in an individual is regarded as a benign phenomenon, not indicative of any particular disease process. However, it is becoming clear that E-IgG are closely associated with autoimmune states.

Serum enzymes and other laboratory tests in acute pancreatitis

This review evaluates selective enzymes and blood tests available for the diagnosis and prognosis of acute pancreatitis. It is concluded that serum amylase and lipase measurements represent the best available diagnostic methods. Newer alternative assays still require careful evaluation.

Comparison of some recent methods for the differentiation of elevated serum amylase and the detection of macroamylasaemia

A pancreatic isoamylase method (Pancreatic Alpha-Amylase EPS, Boehringer) that uses monoclonal antibodies showed almost complete immunoinhibition of salivary (S) amylase activity with only a minor decrease of pancreatic (P) amylase activity. The method displayed good sensitivity and linearity. The correlations of P-amylase activities determined by this technique with a wheat-germ inhibition method and with agarose electrophoresis followed by densitometric scanning were excellent. However, both the wheat-germ and monoclonal inhibition methods failed to detect macroamylasaemia. To recognise macroamylases we used the PEG precipitation method and confirmed the results with agarose electrophoresis. Of 161 serum samples with elevated amylase activities, only four out of five with macroamylasaemia were detected by the PEG precipitation method. No false positives were demonstrated. After PEG precipitation of 28 samples, P-amylase determinations were performed on the supernatants. Again, four out of five with macroamylasaemia were recognised. We consider P-amylase measurement and, when macroamylasaemia is suspected, the combined use of the PEG precipitation method and P-amylase or total amylase determination to be the most practical way to differentiate between elevated serum amylase levels.