Transcript pancreatic-function-tests

D
Pancreatic function tests
FUNCTIONAL ANATOMY OF THE
PANCREAS

The functional unit of pancreas is acinus &
its draining ductule.

The duct epithelium extends into the lumen
of the acinus with centroacinar cell located
b/w ductal epithelium and the acinus.
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The centroacinar cell secretes ions & water.
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The acinus synthesizes,stores,secretes
digestive enzymes.
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On the basolateral membrane lies receptors for
hormones& neurotransmitters that stimulate
secretion of the enzymes.
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The duct epithelium consists of cuboidal cells
and rich in mitochondria for ion transport.
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The duct cells & centroacinar cells contain
carbonic anhydrase,to secrete bicarbonate.
Composition of exocrine secretions
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Inorganic constituents:
Water,sodium,chlorides,potassium,bicarbo
nate.
Water& ions deliver digestive enzymes to
intestinal lumen and help to neutralise
gastric acid.
Pancreatic fluid is colourless,clear,alkaline.
The total daily volume is 2.5 lts.
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Organic components:
The pancreas synthesize digestive
enzymes.
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They are proteolytic,amylolytic,lipolytic &
nuclease digestive enzymes.
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These enzymes are in inactive precursor
forms .
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Activation of these enzymes takes in lumen
of intestine where a brush border glyco
protein peptidases,enterokinases,activate
trypsinogen by removing a N-Terminal hexa
peptide fragment of molecule.
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The active trypsin catalyzes the activation
of other inactive proenzymes.

In addition to digestive enzymes the acinar
cells secrete Pancreatic Secretory Trypsin
Inhibitor(PSTI).
It inactivates trypsins that are
autocatalytically formed in the pancreas that
prevents pancreatitis
Functions of digestive enzymes
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Amylase:
Digests starch & glycogen in the diet.
The amylase hydrolyses 1,4-glycosidic
linkages at every other junction b/w
carbon 1& O2.
The hydrolytic products are maltose
,maltriose& alpha dextrins.
The brush border enzymes complete
hydrolysis to give glucose.
 Lipases:three
lipases
 lipase,phospholipaseA2,carboxylesterase.
 Most
important is salivary,pancreatic,gastric
lipase for fat digestion.
 Pancreatic
lipase digests a triglyceride to two
fatty acids & a monoglyceride.

PhospholipaseA2 catalyses the hydrolysis
of fatty acid ester linkage at carbon 2 of
phosphatidylcholine to form free fatty acid &
lysophosphadidylcholine.

Carboxylesterase cleaves cholesterol
esters ,fat soluble vitamin
esters,tri,di,monoglycerides.
Proteases :
Pancreas secrete variety of proteases that are
activated in the duodenum.
 The activated forms are
trypsin,chymotrypsin,&elastases.
 These endopeptidases cleave specific peptide
bonds adjacent to specific amino acids.
 Also present are
carboxypeptidases,exopeptidases.
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The combined action of proteases & pepsin
result in release of oligopeptides ,free
amino acids.
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These amino acids have effect on
stimulating pancreatic secretion,inhibiting
gastric secretion,regulating small bowel
motility causing satiety.
Tests for exocrine functions:

The first line laboratory tests include
estimation of serum levels of pancreatic
lipase & amylase.

It is easy to diagnose pancreatic
insufficiency in presence of clinical triad of
diabetes,pancreatic calcification &
steatorrhea.
 Most
pancreatic disease remain clinically silent until
90% of gland is destroyed.
 Early
recognition of pancreatic dysfunction may
improve the management of the patients disease and
his / her quality of life .
 The
pancreatic function tests are divided into Direct &
Indirect.
DIRECT INVASIVE INTUBATION TEST
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It requires oro duodenal tube that aspirates pancreatic
secretion from duodenum near Ampulla of Vater
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The stimulants used are secretin , cholecystokinin and
lundh test meal
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The collection period varies from 45 – 125 minutes
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Direct evaluation of pancreatic fluid may include
measurement of total volume , conc of HCO3- /
enzymes
 This
requires pancreatic stimulation by
secretin stimulation followed by CCK
stimulation
Lundh meal test

It assess the response of pancreas to endogenous
secretin and pancreozymin in response to test meal of
5% protein 6% fat 15% carbohydrate and 74% non
nutrient fibre.
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the conc of trypsin and volume of secretin are
measured in the duodenal aspirate in 10 – 20 minute
interval over a period of 2 hrs
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It is simple test , virtually abnormal in pancreatic
insufficiency
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Abnormal result occur when small bowel , liver and
biliary tree disease.
Advantages and disadvantages
 Chemical
and cytological evaluation are performed
on actual secretions
 Cytological
evaluation can establish the presence/
suspicion of neoplasm although precise localization
of primary organ of involvement is not possible
 Because
of advances in imaging techniques
stimulation tests are used less often
Secretin / CCK stimulation test
 Combined
stimulation of Secretin / CCK allows
simultaneous estimation of both HCO3 and trypsin.
 The
test is performed after 6 hr/over night fast .
 Pancreas
is stimulated by iv administration of
secretin 0.25 to 1U/kg followed by CCK
administration.
 The
aspiratescollected at 20,60,80 min interval.
 The
pH,fluid volume,enzyme activities,HCO3 conc
are determined.
 Decreased
pancreatic flow is associated with
pancreatic obstruction.
 Low
concentration of HCO3 and enzymes are associated with
cystic fibrosis,chronic pancreatitis,cysts,calcification and
edema.
Indirect Invasive tests
 ORAL
FUNCTIONAL TEST –
 Bentiromide
test
 Pancreolauryl
 Shilling
test
test
Bentiromide test
 Bentiromide
 It
is a compound attached to PABA
is hydrolysed by pancreatic chymotrypsin in the duodenum
 It
is useful to distinguish patients with pancreatic steatorrhea
from those with normal fat absorption
 Chymotrypsin
hydrolysis of bentiromide liberates PABA which
is absorbed in the proximal small bowel and conjugated in the
liver.
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The PABA conjugates are excreted in the urine .
Urine output of PABA reflects duodenal
chymotrypsin activity.
 Excretion of less than 50% of ingested dose in
6hrs indicates pancreatic insufficiency
 False results occur in intestinal mucosal , hepatic
or renal disease
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Pancreolauryl test
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A tablet containing fluorescein dilaurate is taken
on day 1 and urine is collected for 10 hours. On
day two, a tablet containing fluorescein alone is
given and urine collected again for 10 hours.

Fluorescein dilaurate is hydrolysed by cholesterol
ester hydrolase, present in pancreatic juice.
Fluorescein is absorbed by the intestine, conjugated in the liver, and
excreted in the urine where its fluorescence can be measured.
 Results
are expressed as the ratio of fluorescein excreted after
fluorescein dilaurate and after free fluorescein. A ratio < 20% is
considered abnormal.
 It
detects severe pancreatic insufficiency.
 It
is a rarely used test.
Schilling test
 Principle
–
 Oral
administration of radio active cobolt 57
labelled vitamin B12
 Followed
by IV cold B12 to wash out the
absorbed vitamin in urine
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Excretion of radio activity in urine is a measure
of absorption of vitamin B12 from intestine .
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Hence it is a function of duodenal pancreatic
enzyme activity.
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Chronic pancreatitis gives rise to abnormal
shilling test .
Blood determination test

A) Trypsinogen
proteolytic proenzyme produced exclusively in
the pancreas
 It is detected by radio immuno assay
 Elevated levels are seen in acute pancreatitis or
renal failure
 Decrease levels are seen in severe pancreatic
insufficiency , cystic fibrosis and type I DM
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Amylase
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Is produced and released from salivary glands ,
pancreas , intestine and Genito Urinary Tract
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is particuarly useful in diagnosis of acute
pancreatitis for which the sensitivity is 75 %
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It starts rising in the serum within few hrs of
onset of disease, reaches a peak in 24 hrs and
returns to normal in three to five days with
increased renal clearance
In healthy individuals amylase clearance parallearance
 But
in acute pancreatitis amylase clearance increases as opposed
to creatinine clearance
 Normal
amylase serum level is 50-120 IU/L
– persistent elevation of serum amylase activity
with no apparent clinical symptoms of pancreatic disease
 Macroamylasemia
 It is an early marker
 A rapid rise and fall in
serum amylase in patient with acute abdomen
suggests passage of stone through ampulla of vater
Amylase levels are raised in
Acute pancreatitis
Diabetic keto acidosis
 Burns
 Renal failure
 Perforated duodenal ulcer
 Malignany
 Gall stones
 Ovarian cysts and ruptured ectopics
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Urinary amylase
The increased renal clearance of amylase is
reflected in increase levels of amylase in urine
 Urinary amylase is more sensitive indicator
than serum amylase
 Determination of renal clearance of amylase
is in detecting minor or intermittent increase in
serum concentration of this enzyme

amylase clearance
urinary amylase
% ───────────── = ──────────
creatinine clearance
serum amylase
X
serum creatinine
──────────── x 100
urinary creatinine
Normal range: 1.0 -3.1%
Acute pancreatitis: 4.0-12%
Lipase
 Hydrolyses
neutral fat to fatty acids and
monoglycerides .
 In
acute pancreatitis lipase levels are very high ( 2 -5
times the normal amount ).
 There
is a rapid rise of lipase level in blood after attack
and persists for 7 – 14 days.
Therefore
lipase estimation has advantage over amylase
estimation
Elevated
lipase levels are also seen in peptic ulcer ,
malignancy, renal failureand salivary gland inflammation
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Lipase levels are also used in diagnosis
and follow up of cystic fibrosis ,coeliac
disease and crohnsdisease.
Low lipase levels indicate pancreatic
destruction and associated with DM
Lipase deficient people have high
cholesteryl triglycerides , high blood
pressure , difficulty losing weight and
varicose veins .
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Sensitivity of amylase and lipase test for
detection of acute pancreatitis is 91 and
94% respectively.
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Normal lipase levels: 50-175 IU/L.
TESTS FOR FAECAL FAT
It involves 72 hr fecal fat determination.
Individuals on lipid free diet excrete 1-4gm lipid in 24 hr
period.
Even with lipid rich diet, fecal fat will not exceed 7 gms in 24
hr period.
The pt is placed on 100gm/day fat diet and stool is collected
daily for 3 days.
Individual with normal pancreatic fn excrete < 7 % of total fat
ingested while in pancreatic insufficiency, pts excrete > 20 %
of fat.
CONTD
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Although steatorrhoea occurs in mucosal
malabsorption it is not as great as that encountered
in pancreatic insufficiency.
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Qualitative test :- Visualisation of fat droplets / free
fatty acids under the microscope using fat stains.
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Normal feces have 40-50 neutral lipid droplets/HPF.
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Steatorrhoea is characterised by increase in numb &
size of droplets.
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Quantitative:- Confirmatory test for Steatorrhoea.
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The pt is put on high fat diet atleast 2 days prior to
fecal collection & stools are collected for 72 hrs.
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The fecal fat is analysed by Titrimetric & Gravimetric
methods.
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Titrimetric Method involves saponification of fecal
lipids with hydroxide and then conversion of salts of
FA to FFA with acid treatment.
 Gravimetric
method:- involves extraction of
total fecal lipids in organic solvent followed
by their physical measurement by sensitive
balance.
Faecal elastase

FE is increasingly being used as a noninvasive first line test to diagnose exocrine
pancreatic insufficiency.
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Faecal Elastase is a proteolytic enzyme
secreted by the acinar cells of the
pancreas.
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Elastase-1 is not degraded during intestinal
transit, so the stool conc. reflects exocrine
pancreatic function.
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Values > 200 µg elastase/g stool indicate normal
exocrine pancreatic function.
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Values < 200 µg elastase/g stool indicate
exocrine pancreatic insufficiency.
Sweat electrolyte determination
Estimation of sweat and skin electrolytes is
helpful in the diagnosis of cystic fibrosis.
 Two to five fold increase in sweat
sodium,chloride are diagnostic.
 No other condition will cause increase of sweat
chloride,Na above 80 mEq/L.
 Sweat potassium is also increased but less
significant.
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Tests For MALABSORPTION

The Pancreatic Malabsorption has to be
differentiated from GI Malabsorption.
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Among the absorption tests Starch Tolerance & DXylose test provide useful information
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Starch Tolerance test:- Pancreatic Amylase
deficiency in intestine should compromise the
hydrolysis of carbohydrates and hence after oral
ingestion of starch.There is rise in Bl.Glucose,
which is lower than normal individuals.
Pts with Pancreatic Malabsorption show flatter STT
curve.
D-Xylose Test:- D-Xylose is valuable in
differientiating malabsorption
25gm of d-xylose in water is ingested orally &amount
excreted over 5hr period in urine is determined.
If amount excreted is <3gm% the diagnosis is mostly
enterogenous malabsorption.

Because pancreatic enzymes are not
required for absorption of xylose.
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Accuracy of this test depends on rate of
absorption & rate of excretion.
 Faecal
 In
nitrogen:
pancreatic disease with diminished
secretion of protein splitting enzymes the
faecal nitrogen may be increased
Fecal Chymotrypsin & Elastase 1:
Chymotrypsin in stool is an indirect test to
establish pancreatic insufficiency in pts with
Cystic Fibrosis.
 Measurement of pancratic elastase 1 in stool
using Monoclonal antibody against human
elastase 1 has received significant interest.
 But this test is not sensitive in detecting mild to
moderate disease.
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Other indirect tests that have been used are
Triglyceride & Cholestryl breath test , H2 & CO2
breath test, plasma measurement of pancreatic
polypeptide & Amino acids.
 Measurement of Leucine aminopeptidase is
elevated in Ca Pancreas.Other tumour markers
include CEA,AFP,Pancreatic onco fetal antigen.
 However these tests prove less sensitive than
other indirect tests.
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