4. Elastase: Digests elastin, which is the most resistant of

all body proteins to lytic agents.

Peptidases

1. Carboxypeptidase: The active enzyme removes amino

acids one by one from the carboxyl ends of the peptide

chains.

2. Aminopeptidase: The active enzyme removes amino

acids one by one from the ends of the peptide chains

bearing the free amino groups.

Nucleases

Ribonuclease and deoxyribonuclease are secreted in

probably more than one or perhaps several forms, they

hydrolyze the respective nucleic acids.

Amylolytic Enzymes

Amylase: Alpha amylase attacks the alpha-1-4-glycosidic

bonds of starches breaking them down to the disaccharide

maltose.

Lipolytic Enzymes

1. Lipase: It partially hydrolyzes neutral fats, splitting off

one fatty acid at a time, thus forming diglycerides and

monoglycerides along with liberated free fatty acids. Its

optimum pH range is 7 to 9. This enzyme is activated

by biliary contents. It shows optimal activation when

the substrate is in emulsified form rather than in true

solution form. The emulsifying action of bile salts and

bile acids is very helpful for optimal enzymic action.

2. Lecithinase (phospholipase): Phospholipases A and

B act in succession. Both of these remove fatty acids,

the end products formed from lecithin and cephalin

are glyceryl phosphoryl choline, glyceryl phosphoryl

ethanolamine and glyceryl phosphoryl serine.

Acute Pancreatitis

Acute pancreatic necrosis (acute hemorrhagic pancreatitis)

has over 50% mortality rate. It is known to be related to

gallstones, alcoholism, trauma, infection (mumps), renal

transplantation, various metabolic disorders, e.g. hyperlipidemia, uremia and hyperparathyroidism.

Serum amylase estimation has been widely used in

the diagnosis of acute pancreatitis. Serum amylase activity

rises within hours following an episode. Values over 5 times

the upper limit of normal are suggestive of the diagnosis.

Values may return to normal within 5 days following a mild

edematous attack. Persisting elevated values longer than

this suggest continuing necrosis or possible pseudocyst

formation. The urine amylase activity rises promptly, often

within several hours of the rise in serum activity. Values

over 1,000 units per hour (in urine) or higher are seen,

almost exclusively in patients with acute pancreatitis.

Amylase activity in blood (or in peritoneal fluid in

certain conditions) may be raised to 1,000 Somogyi units

in various (nonpancreatic) disorders as: (i) intestinal

obstruction, strangulation, or perforation, (ii) following

upper abdominal surgery, (iii) ruptured ectopic pregnancy,

(iv) mumps, (v) renal insufficiency, and (vi) following

morphine administration. Values over 5,000 units suggest

a diagnosis of acute pancreatic necrosis.

Chronic Pancreatitis (Cirrhosis of Pancreas)

There is variable degree of fibrosis and atrophy in the

pancreatic parenchyma. Diagnosis as in the case of acute

pancreatitis, depends in part on determination of amylase

activity in serum and urine.

Carcinoma of Pancreas

Serum amylase may be elevated but is of little diagnostic

importance.

Lipase

This is an esterase acting on ester linkages in triglycerides.

Bile salts and calcium enhance its activity. Lipase occurs

predominantly in the pancreas, but small amounts are

produced in the gastric and small bowel mucosa.

Principle (Lipase estimation in serum)

The classic method of serum lipase determination is that

of Cherry and Crandall using olive as substrate, overnight

incubation (24 hours), and titration of liberated fatty

acids with sodium hydroxide, using phenolphthalein

as indicator. Normal range of values is up to 1.5 units in

serum.

The method given above takes a long time and if the

report is to be given on emergency basis—a rapid (20 minute

incubation) specific turbidimetric method is available.

The disadvantage of this method is spuriously high results

432 Concise Book of Medical Laboratory Technology: Methods and Interpretations obtained in the presence of jaundice. By this method,

values above 10 units are doubtful, above 19 units definitely

abnormal.

Interpretation

Acute pancreatitis: Serum lipase activity rises slower than

that of amylase, sometimes as late as 24 to 48 hours after

onset, often peaking on the fourth day. It may remain

elevated longer than the serum amylase. Eventhough,

it is less sensitive than the serum amylase, it provides

confirmatory evidence for the diagnosis when positive.

Elevation in patients with mumps strongly suggests

significant pancreatic as well as salivary gland involvement

by the disease.

Chronic pancreatitis: Serum lipase estimation is of relatively little value in the diagnosis of chronic pancreatitis.

Pancreatic carcinoma: Serum lipase is elevated more

often in patients with pancreatic carcinoma than is serum

amylase, although not with sufficient frequency to make it

of much value diagnostically.

Secretin Test

A double lumen tube, providing for separate aspiration

of gastric and duodenal contents, is passed into the

duodenum, using fluoroscopic guidance and maintaining

constant aspiration of gastric contents. Duodenal contents

are aspirated until clear. The patient is then given IV one unit

of secretin per kg of body weight, and pancreatic secretion

entering the duodenum is collected for 80 minutes. The

aspirate is examined for volume, bicarbonate content, and

amylase activity.

The test is not employed for the diagnosis of acute

pancreatic necrosis (it would be hazardous). Patients

with chronic pancreatitis are unable to secrete juice

of high bicarbonate content (less than 90 mEq/L). As

in the case of chronic pancreatitis, this test may assist

in diagnosis of pancreatic carcinoma tumors of head

of pancreas tend to depress the overall volume flow

(lower limit of normal—2 mL per kg body weight per

80 minutes). In carcinoma body of pancreas half the

patients may show normal volume, carcinoma of tail

does not affect the volume.

Patients with ductal obstructive lesion may exhibit

elevation of serum amylase during and following the

test, normally there is no elevation of serum amylase

activity. The pattern of increased volume with decreased

bicarbonate and normal amylase has been associated

with hemochromatosis. Rarely, an increase in the amylase

with normal bicarbonate concentration and volume flow

has been noted in patients with nutritional and metabolic

pancreatic fibrosis as well as in pancreatitis associated with

inflammatory disease of the intestines. In some patients of

pancreatic ductal obstruction, levels may rise.

Tumors of the head of the pancreas associated

with jaundice must be differentiated from nonsurgical

cholestatic liver disease, from carcinoma, obstructing

stone, or other obstructing pathologic lesions of the

common bile duct, and from ampullary carcinoma.

Duodenal aspirate containing cholesterol crystals or

calcium bilirubinate pigment and pus, especially when

associated with a normal secretin test, suggest gallstone

etiology. However, a duodenal aspirate containing calcium

bilirubinate pigment is not specific for cholelithiasis.

Unremittent jaundice, alcoholic duodenal fluid and stools,

consistently negative urine urobilinogen tests, and less

than 5 mg fecal urobilinogen per 24 hours, associated

with a normal secretin test, suggest carcinoma of the

common bile duct or gallbladder. Intermittent jaundice

and presence of blood in the aspirate suggest carcinoma of

the duodenal papilla, especially when associated with an

abnormal secretin test. Cytologic examination of aspirate

may be helpful in the diagnosis of carcinoma, as are the

results of enzyme and volume outputs.

Other Laboratory Tests in Acute Pancreatitis

¾ Leukocytosis in patients with acute pancreatitis (up to

30,000/mm3

).

¾ Hemoconcentration, so raised hemoglobin.

¾ Serum levels of lecithinase A, trypsin and deoxyribonuclease activity are also elevated.

¾ A falling serum calcium points to the more serious form

of pancreatitis as does turbidity of serum.

¾ In alcohol-related pancreatitis serum bilirubin may rise.

¾ Transient hyperglycemia may also occur.

Miscellaneous Tests for Chronic Pancreatitis

Various tests for malabsorption can be done

¾ Serum carotenoid level

¾ Glucose tolerance test

¾ Three-day fecal fat determination

¾ Gross and microscopic examination of stool

• 131I triolein test

• D-xylose test.

SWEAT ELECTROLYTES PILOCARPINE

IONTOPHORESIS

Pilocarpine is iontophoresed into the skin to stimulate

locally increased sweat gland secretion. The resulting

Examination of Gastrointestinal Contents 433

sweat is absorbed by filter paper, diluted with distilled

water and analyzed for sodium and chloride contents. The

method is painless and reliable. Total body sweating is

hazardous in cystic fibrosis patients.

Diagnostic Application of Sweat Testing

Fibrocystic disease of pancreas (Mucoviscidosis)

This is a familial, Mendelian recessive disease characterized by abnormal secretion by the various exocrine

glands of the body, including pancreas, salivary glands,

peritracheal, peribronchial and peribronchiolar glands,

lacrimal glands, sweat glands, mucosal glands of small

intestine and even the bile ducts.

Laboratory diagnosis depends largely upon demonstration of increased sodium and chloride in the sweat,

found in almost 99% of patients. Screening tests for sweat

chloride have also been used and depend upon hand

imprints on silver nitrate containing agar or paper. The

sweat chloride precipitates with silver, and the intensity

of the print is roughly proportional to the sweat chloride

precipitation. However, chemical estimation of sweat

chloride is more accurate.

In adult males values of sweat chloride up to 70 mEq/L

and in females up to 65 mEq/L are normal.

Normal values in children

Chloride Sodium

Below 50 mEq/L: Normal Below 70 mEq/L: Normal

50-60 mEq/L: Equivocal 70-90 mEq/L: Equivocal

Over 60 mEq/L: Abnormal Over 90 mEq/L: Abnormal

17