Intro to GI Lab Tests

Question 1

CBC - White Blood Cell

Answer 1

• Increased with infections, pain, alcoholic hepatitis, or stress.
• Decreased with viral infections

Question 2

CBC - Platelets

Answer 2

• Decreased in cirrhosis

Question 3

CBC - Hemoglobin (Hgb) and Hematocrit (Hct)

Answer 3

• Decreased with GI bleeding (celiac, IBD, cancer)

Question 4

INR

Answer 4

• Elevated in liver disease

Question 5

Anemia

Answer 5

• Macrocytic - B12, folate deficiency (think malabsorption, ETOH)
• Microcytic - think Fe deficiency
• Consider iron studies: serum iron, iron binding capacity and ferritin

Question 6

Inflammatory Markers

Answer 6

• CRP, ESR
• can be useful in IBD

Question 7

Aminotransferases

Answer 7

• Important in production of amino acids
• Located in hepatocytes
• Markers of cell injury
• Inflammation = increased permeability that leads to leak
• ALT and AST

Question 8

ALT

Answer 8

• Alanine aminotransferase
• Normal Range: 1-45
• More specific for the liver

Question 9

AST

Answer 9

• Aspartate aminotransferase
• Normal Range: 7-42
• Less specific - seen in liver, muscle, kidney

Question 10

Alkaline Phosphatase

Answer 10

• Bile canicular membrane (also seen in bones, intestines, placenta)
• Increased in conditions like neoplastic, infiltrative liver disease, cholestasis (retention of bile acids in the liver) and partial or complete bile duct obstruction
• Also increased with bone regeneration or pregnancy

Question 11

Y-glutamyltransferase: GGT

Answer 11

• Hepatocyte membrane enzyme
• Helpful to discern if Alk Phos is elevated because of liver disease
  
  • Increase alk phos and normal GGT suggests nonhepatic cause. Order alkalin phos isoenzymes
• Increased with alcohol use (helps identify unreported use)

Question 12

Bilirubin

Answer 12

• Water-insoluble product of heme metabolism
• Conjugated in the hepatocytes (glucuronic acid) makes it water soluble, allowing excretion in bile.
• Serum level: direct (conjugated) or indirect (unconjugated)
• Overproduction of bilirubin: hemolysis, resorption hematoma. 20% or less conjugated
• Hepatic dysfunction or impaired bile flow. 20-80% conjugated

Question 13

Prothrombin Time (PT)

Answer 13

• Measure of activity of coagulation factors II, V, VII, and X
  
  • All are synthesized in the liver and all are vitamin K dependent

Question 14

Albumin

Answer 14

• Marker of liver protein synthesis
• Half-life = 21 days
• Decreases due to liver dysfunction, does not occur acutely
• Acute decrease is seen with sever systemic illness

Question 15

Amylase and Lipase

Answer 15

• Markers of pancreas inflammation
• Amylase rises quicker with pancreatitis
• Lipase remains elevated longer with pancreatitis

Question 16

Electrolytes

Answer 16

• Sodium, potassium, bicarbonate, chloride
• Vomiting is associated with hypochloremic metabolic alkalosis (reduced HCl)
• Diarrhea is associated with hypokalemia
• Dehydration results in hypernatremia

Question 17

Stool Tests

Answer 17

• Stool Cultures
• Clostridium difficile toxin
• Ova and parasites
• Fecal leukocytes