GI Lab Medicine Flashcards
What lab result is greatly increased in the early phase of acute pancreatitis?
Amylase
Greatly increased (>3x ULN) in early phase of acute pancreatitis
Within 3‐6 hours of onset of abdominal pain
Tends to return to normal after 3‐5 days
What are two non-GI etiologies of increased amylase?
Current mumps infection, or salivary stones
What lab is more accurate than amylase for the diagnosis of acute pancreatitis?
Lipase
~98% specific if level is >3x ULN
~Also, remains elevated for up to 14 days, so useful for delay in seeking care
What are two non-GI etiologies of increased lipase?
DKA
HIV
Which is more specific and which is more sensitive, of amylase and lipase?
Amylase: more sensitive
Lipase: more specific
What is bilirubin?
Breakdown product of RBCs, specifically “heme”
Overproduction (hemolysis) or underexcretion (liver problem)
If you see a lot of indirect/unconjugated bilirubin, what does that tell you?
Increased bilirubin production -
hemolytic anemia, transfusion reaction
What is the most common cause of an “unimportant” increased indirect/unconjugated bilirubin?
Gilbert’s syndrome
If you see a lot of direct/conjugated bilirubin, what does that tell you?
Liver dysfunction:
~hepatitis cirrhosis
Biliary obstruction:
~gallstones, pancreatitis
Where does alkaline phosphatase originate?
bone, liver
How do you determine if an isolated elevated alkaline phosphatase is hepatic or bone origin?
GGT
~GGT elevated means alk phos elevation is from liver disease
~GGT normal means alk phos elevation is from bone
How can you help confirm an alcoholic liver etiology? (corresponding to acute alcohol use)
AST/ALT elevated in ratio of 2:1, elevated GGT
GI etiologies of elevated alkaline phosphatase
Obstruction – gallstone,
hepatic/pancreatic cancer
Non-GI etiologies of elevated alkaline phosphatase
Bone:
Paget’s disease, metastatic bone tumor, osteomalacia, rickets
Where does lactic acid dehydrogenase originate?
Intracellular enzyme widely distributed in all tissues of the body
What is the GI clinical significance of elevated LDH?
In GI setting, think:
Ischemic bowel
Liver disease (cirrhosis, alcoholism, acute viral hepatitis)
May be significantly elevated in hemolysis / accompany an increase in unconjugated bilirubin
Total protein may be increased in:
Marked dehydration
~hemoconcentration from vomiting, diarrhea
Total protein may be decreased in:
~chronic liver disease ~nephrotic syndrome ~IBD ~severe dietary protein deficiency ~malabsorption ~alcoholism ~acute burns
What is the source of albumin?
Synthesized by liver, so measurement can reflect the liver’s biosynthetic capacity
How is albumin level useful?
Consider chronic liver disease if below 3g/dL
Level indicates severity in chronic liver disease
In what liver conditions is albumin usually normal?
~acute viral hepatitis
~drug-related hepatotoxicity
~obstructive jaundice
What is the source of gastrin?
Hormone secreted by the antral G cells in stomach mucosa, stimulating gastric acid production
Follows circadian rhythm, fluctuates in relation to meals
Etiologies of increased gastrin levels
Hypo/Achlorhydria (most common)
Gastrinoma (Zollinger‐Ellison syndrome, levels >10x normal)
H. pylori is bad because it invades the intestinal mucosa.
T/F
FALSE
Generally does not invade gastroduodenal tissue
Renders the underlying mucosa more vulnerable to acid peptic damage
Host immune response to H. pylori incites an inflammatory reaction which further perpetuates tissue injury
What are the gold standard and the preferred tests for H. pylori?
gold standard: tissue biopsy
preferred: Urea Breath Testing (UBT)
What medications interfere with the results of a gastrin level test?
Must be off H2 blockers for 24 hours; off PPIs for 6 days
What is the procedure for a Urea Breath Test and how does it work?
Hydrolysis of urea into CO2 and ammonia by H. pylori
Patient drinks a labeled urea solution & blows into a tube
If H.pylori is present, the urea is hydrolyzed and labeled CO2 is detected in breath samples
What medications must be stopped before doing a Urea Breath Test?
Off antibiotics/bismuth for 4 weeks; antacids for 2 weeks
What is the gold standard for diagnosis of celiac disease?
small bowel biopsy
You do celiac antibody testing when the patient has not eaten gluten for 14 days.
T/F
FALSE
Test while patient is on gluten‐rich diet
If already gluten‐free, resume consumption of
gluten for 2‐12 weeks before testing
After gluten‐free diet is initiated, Ab levels remain elevated for 1‐12 months
Can test if recently went gluten‐free
What antibody is pathognomonic for celiac?
Presence of IgA EMA is pathognomonic for celiac
When would you order a stool culture?
When suspect bacterial etiology
Salmonella, Campylobacter, Shigella
When would you order a fecal lactoferrin?
Used most widely in assessing patients with IBD
What is the significance of fecal leukocytes?
Usually present in patients with stools containing blood and mucus / infection with invasive organisms
If positive, patients may merit more extensive diagnostic evaluation / possibly empiric antibiotic therapy
When would you order ova & parasite testing?
Suspect parasitic etiology
Giardia, Entamoeba histolytica, Cryptosporidium
What is the most common test for C.diff and how effective is it?
Most common test is assay for antigen in stool
High specificity (typically >95%)
Low sensitivity (60‐95%)
If negative result: repeat 1‐2 times
What is the gold standard test for C.diff? (not most common test, just gold standard test)
Gold standard is cell cytotoxicity assay
Detects toxin by its cytotoxic effect in cell cultures
Sensitivity = 94‐100%
Specificity = 99%
Lab dependent, high cost, delay 1‐3 days
With acute diarrhea, what criteria would lead you to do further testing rather than simply recommending supportive therapy?
- Severe illness: T>38.5C, abd pain, bloody, >6 stools/24h, dehydration
- Immunocompromised: AIDS, post-transplant
- Patient > 70 yrs of age
If you determine that further testing is necessary for acute diarrhea, what do you do?
- Fecal leukocytes
- Routine stool culture
- C.diff assay if recent hosp or abx
- O & P if:
~diarrhea > 10 days
~travel to endemic region
~community water-borne outbreak
~HIV infection or MSM
What are two etiologies of fecal fat?
celiac disease
pancreatic insufficiency
Dietary fat should be restricted before performing a fecal fat test.
T/F
FALSE.
Dietary fat should be at least 50–150 g/d for 2 days before collection
All stools should be collected for 72 hours and refrigerated
What are two etiologies of fecal occult blood?
~GI bleed (upper or lower)
~colon cancer
What can cause a false negative fecal occult blood test?
vitamin C
What is the purpose of SAAG testing?
To determine whether ascites is caused by portal hypertension.
A high SAAG (> 1.1 g/dL) indicates patient’s ascites is due to portal hypertension with 97% accuracy.
A low SAAG (< 1.1 g/dL ) indicates ascites not associated with increased portal pressure, e.g. TB, pancreatitis, nephrotic syndrome.
What is the test used to screen for immunity to Hepatitis B?
~look for a positive anti-HBsAg blood serum level
~this antibody appears in most individuals after clearance of HBsAg and after successful vaccinations
If a patient has both elevated GGT and MCV, what is most likely?
serious drinking problem
