Liver Pseudofunction Tests

Hepatic insufficiency

the liver is unable to meet the demands of the body

WHat can cause decreased functional liver mass?

• infection/inflammation

  • distortion of architecture

• toxins

  • distortion of architecture

• necrosis

  • potential to regenerate

• metabolic disease

  • hepatocytes filled with lipid or glycogen

• PSS

  • small liver due to growth factors not reaching it

• neoplasia

• congenital liver disease

Cirrhosis

fibrosis with regenerative nodules

Acquired PSS

openings of intrahepatic and extrahepatic communication between portal and systemic vessels

What congenital diseases lead to decreased liver function?

• Congenital hepatic cysts - Persian cats and horses

• Copper hepatopathy - copper transport mutation

• Hepatoportal Microvascular dysplasia

  • C/S similar to PSS but with dysplastic microvasculature

C/S of hepatic insufficiency

• neurological

• ascites - transudate

• prolonged effects of drugs or anesthetics

What are the pseudofunction tests?

• hypoalbunemia

• hypoglycemia

• low BUN

• hypocholesterolemia

• Ammonia urate crystals or uroliths in urine

WHat is a pseudofunction test?

Tests on a general serum chemistry panel that, taken together, can indicate liver insufficiency / functional liver failure

True or False: Hypoalbunemia is not common in horses with chronic liver disease.

TRUE

WHy would you see decreased glucose with liver insufficiency?

Liver is responsible for glucose uptake and storage as glycogen after a meal and synthesis of glucose (gluconeogenesis); decreased synthesis

Why would you see decreased BUN with hepatic insufficiency?

decreased production from ammonia and protiens

You see _____cholesterolemia with cholestasis and _____cholesteroemia with hepatic insufficiency.

hyper; hypo

What are the non-hepatic reasons for the alterations discussed?

• Hypoalbuminemia

  • decreased intake

  • loss thru GI or kidneys

• Low BUN

  • decreased intake (low protein diet)

• Hypoglycemia

  • decreased intake

  • pancreatic tumors

  • insulin administration

What should you always do prior to a liver biopsy? Why?

coagulation testing because the liver makes coagulation and anticoagulation factors

What hematological changes are associated with liver disease?

• anemia

  • nromocytic, normochromic non-regenerative (chronic dz)

  • microcytic normochromic (PSS or functional iron deficiency)

• Acute severe intravascular hemolysis

  • fulminant liver failure (horses)

  • copper poisoning (sheep)

What are some abnormal RBC shapes you may see with liver insufficiency?

• Acanthocytes w/o anemia

• Acanthocytes with regenerative anemia

  • fragmentation injury or microangiopathic hemolysis

• Target cells

  • cholesterol and lipids added equally to inner and outer leaflets

What is the most specific test fr decreased functional mass?

Bile acids in enterohepatic circulation

When is total serum bile acids indicated?

for non-icteric dogs and cats suspected to have congenital or acquired PSS or hepatic insufficiency

What collection tubes should you use for bile acids?

red top or green top

When are the samples collected?

before eating a meal - fasting bile acids

2hrs after eatin a small meal - post-prandial

What is the purpose of the small meal in the bile acids test?

to cause cholecystokinin production/release and gall bladder contraction

Feeding too large of a meal can induce:

lipemia

What are the imitations of bile acid testing?

• no useful information for icteric patients

• significant hepatocellular injury/necrosis can cause impaired processing of bile acids even tho liver is functional

• cholestasis can regurg bile acids even thogh not a function problem

What can caue falsely low post prandial bile acids?

• meal does not cause gall bladder to empty

• delayed intestinal transit

• rapid intestinal transit

• malabsorption due to concurrent intestinal disease

What does it mean if fasting bile acids is higher than post prandial bile acids?

spontaneous gall bladder emptying before gving the meal

True ot False: Liver disease in horses has non-specific C/S.

TRUE

How many samples do you need to run bile acids in horses?

1 bc no gallbladder

A serum bile acid above ____ is abnormal in horses.

25

Ammonia is a byproduct of:

protein metabolism, catabolism of amino acids, nucleic acids, nitrogenous wastes

C/S of hyperammonemia

• hepatic encephalopathy

  • behavior changes

  • seizures

  • head-pressing

  • stupor

  • coma

  • death

What are the sample handling techniques for blood ammonia?

• fasting sample (8hrs)

• whole blood in EDTA or lithium heparin tube (NOT ammonium heparin)

• harvest plasma immediately

• assay within 1 hr or refrigerate for assay later

• DO NOT THAW during transportation to lab

What can cause a false increase in ammonia results?

• hemolysis or delayed separation result

• interferences (lipemia, hemolysis, icterus)

• contamination of the sample or analytic equipment

• ARTIFACT (most common)

What can cause a false decrease in ammonia levels?

• sample handling error

  • exposure to air

What liver diseases can cause increased plasma ammonia?

• PSS

• hepatic insufficiency

True or False: Increased ammonia is pathognomonic for liver disease.

FALSE - must be used with other informaton

What diseases cause increased ammonia levels that are not related to the liver?

• high protein meal

• recent strenuous exercise

• gut dysbiosis

• urea toxicity in cattle

• hyperammonemia in horses without liver disease

• inherited urea cycle disorder

How do you perform an ammonia tolerance test?

1. fast and collect baseline sample

2. administer ammonium chloride at 100mg/kg via stomach tube

3. collect sample 30 min later

Note: do not exceed 3g total dose

When is an ammonium tolererance test used?

in animals suspected of portosystemic shunt but fasting ammonia is not increased

When should an ammonia tolerance test not be performed?

in animals with fasting/resting Hyperammonemia. You may kill the patient