Lab Tests
Overview
Early diagnosis of
pancreatic cancer is difficult, even with recent advances in diagnostic
methods. Symptoms develop gradually and steadily, and are often present for
many months before diagnosis. Physicians typically use a range of imaging
studies to confirm the diagnosis. Tumor markers (substances in the body that
indicate the presence of tumors) do not permit early diagnosis of pancreatic
cancer, but on follow-up are used to indicate the presence of tumors.
The following tests
are often used when pancreatic cancer development is suspected, or when the
patient state is monitored before, during, and after cancer treating procedures:
- Comprehensive metabolic panel: a group
of tests that may be used to evaluate why someone is jaundiced, to detect
elevated levels of bilirubin and liver enzymes, and to monitor liver and
kidney function.
- CA 19-9 (Cancer Antigen 19-9): a tumor
marker for pancreatic cancer; it may be used to monitor for cancer
recurrence but is not useful for detection or diagnosis.
- CEA (Carcinoembryonic antigen): a tumor
marker used as a monitoring tool.
- Calcium:
this is sometimes raised in pancreatic cancer (as in other cancers),
producing symptoms such as weakness, nausea, abdominal pain and thirst. Raised
calcium caused by cancer can be treated and the symptoms relieved.
- Other tests, such as fecal fat, stool trypsin, trypsinogen, and lipase, may be ordered to help evaluate how well the pancreas is functioning and to determine whether pancreatic enzyme supplementation is necessary.
Some of the tests
are reviewed below in more details.
CA 19-9
CA 19-9 (carbohydrate
antigen 19-9) is not sensitive or specific enough to use as a screening test
for cancer, and it is not diagnostic of a specific type of cancer. CA 19-9 is
the mainstay tumor marker and is ordered when pancreatic cancer is suspected,
particularly if the patient shows signs of jaundice (yellowing of the skin):
- To help differentiate between cancer of
the pancreas and other conditions, such as pancreatitis
- To monitor a person's response to
pancreatic cancer treatment and/or cancer progression at the course of the
disease following surgery, chemotherapy, or radiotherapy, normalizing or
decreasing soon after treatment.
- To watch for pancreatic cancer
recurrence.
Low amounts of CA
19-9 can be detected in healthy people, and many conditions that affect the
liver or pancreas can cause temporary elevations. Moderate to high levels are
found in pancreatic cancer, other cancers, and in several other diseases and
conditions. The highest levels of CA 19-9 are seen in cancer of the exocrine
pancreas. This cancer arises in the tissues that produce food-digesting enzymes
and in the ducts that carry those enzymes into the small intestine. About 95%
of pancreatic cancers are of this type.
Serial measurements
of CA 19-9 may be useful during and following cancer treatment. Rising or
falling levels may give the doctor important information about whether the
treatment is working, whether all of the cancer was removed successfully during
surgery, and whether the cancer is recurring. However, additional diagnostic
methods are required because this test is only 70 percent sensitive and 87
percent specific for pancreatic cancer.
Serum Bilirubin
This test is a
measure of the bilirubin in the blood.
Normal Value: total
bilirubin = less than 1.5 mg/100ml
Clinical
Implications: Bilirubin is
present in blood at all times due to the breakdown of hemoglobin which occurs
all the time. Normally, bilirubin is removed from the blood by the liver.
Increased serum bilirubin levels indicate obstructive disease of the liver,
hemolysis or actual liver cell damage.
CEA
CEA is used mainly
to monitor the treatment of cancer patients, especially those with colon cancer.
Following surgery, CEA values are helpful in monitoring the response to therapy
and in determining whether the disease has recurred. CEA is also used as a marker
for other forms of cancer, including cancers of the rectum, lung, breast,
liver, pancreas, stomach, and ovary. Not all cancers produce CEA, and a
positive CEA test is not always due to cancer. Therefore, CEA is not used for
screening the general population.
Assessment of
pancreatic function
In pancreatic
cancer, abnormal digestion associated with inadequate pancreatic enzymes and
function (insufficiency) can occur. When pancreatic enzyme levels fall below 1
percent to 2 percent of normal, poor nutrient digestion and incorporation
occur. Poor digestion can cause significant weight loss, nutritional
deficiencies, and foul-smelling or greasy bowel movements. It is also
associated with changes in gastrointestinal function, such as changes in
acid-base balance, bile acid metabolism, stomach emptying, and motility of the
intestine.
Tests for pancreatic enzyme function are sensitive for moderate-to-severe pancreatic insufficiency, but are
of limited value in mild pancreatic impairment.
- Bicarbonate secretion is probably the
single most useful measure of pancreatic enzyme function. Indirect
estimation can be done via the 72-hour fat balance test, which determines
fat losses as a percentage of daily fat intake.
- Measuring the activity of pancreatic chymotrypsin
(a pancreatic enzyme).
- A test in which oral fluorescein
dilaurate is broken down by esterase, a pancreatic enzyme.
- Fecal elastase-1 is a simple,
non-invasive, and robust test of fat balance in the body.
- Cholesteryl-[14C]octanoate breath test.
Testing Pancreatic
Enzymes: Amylase
Amylase is an enzyme that is synthesized primarily in the
pancreas and salivary glands. Amylase (alpha-amylase or AML) helps to digest
starch and glycogen in the mouth, stomach, and intestine. In cases of suspected
acute pancreatic disease, measurement of serum or urine AML is the most
important laboratory test.
Normal serum amylase results: 25 to 160 U/L
**Please note: There are more than 20 different lab methods
for determining the results of this test. Be sure to use the normal values at
your facility. Be sure to withhold drugs that elevate AML levels such as
aspirin, asparaginase, azathioprine, corticosteroids, cyprohepadine, narcotic
analgesics, oral contraceptives, rifampin, sulfasalazine, and thiazide or loop
diuretics. If they cannot be withheld, note them on the lab slip.
After the onset of acute pancreatitis, AML levels begin to
rise within 2 hours, peak within 12 to 48 hours, and return to normal within 3
to 4 days. Determination of urine levels should follow normal serum AML results
to rule out pancreatitis. Moderate serum elevations may accompany obstruction
of the common bile duct, pancreatic duct, ampulla of Vater, pancreatic injury
from a perforated peptic ulcer, pancreatic cancer, or acute salivary gland
disease. Impaired kidney function may increase serum levels.
Testing Pancreatic
Enzyme: Lipase
Lipase is produced by the pancreas and secreted into the
duodenum, where it converts triglycerides and other fats into fatty acids and
glycerol. The destruction of pancreatic cells, which occurs in acute
pancreatitis, causes large amounts of lipase to be released into the blood.
This test is used to measure serum lipase levels. It is most useful when
performed with a serum or urine amylase test.
Normal value: 56 to 239 U/L (depending on method)
Prior to the test, withhold cholinergics, codeine,
meperidine, and morphine. If these drugs cannot be withheld, note their use on
the lab slip when the specimen is sent to the lab.
High lipase levels suggest acute pancreatitis or pancreatic
duct obstruction. After an acute attack, levels remain elevated for up to 14
days. Lipase levels may also increase in other pancreatic injuries, such as
perforated peptic ulcer with chemical pancreatitis due to gastric juices, and
in patients with high intestinal obstruction, pancreatic cancer, or renal
disease with impaired excretion.
Sources and Additional
Information:
