18: Enzymes

Leakage enzymes for muscle injury

CK and AST

CK

Creatine kinase

Source of CK

Muscle cell leakage enzyme

AST

Aspartate aminotransferase

Source of AST

Muscle and liver cell leakage enzyme

Unit of measurement for enzymes

International units (IU) per liter (IU/L)

How do we measure enzyme activity

Evaluating substrate conversion

When do we consider an increase in enzymatic activity significant

>2x RI

Leakage enzyme that is most specific for muscle injury

CK

Type of muscle injury that is commonly caused by ischemic necrosis

Rhabdomyolysis

RBC abnormality commonly associated with snake bites

Echinocytes

Clinicopathologic abnormality that WILL accompany hemoglobinuria

Anemia- if you have enough RBC lysis for it to show in the urine, you will have anemia

Why do you have to diurese a patient with severe muscle damage

To prevent pigment nephropathy from all the myoglobin

How do CK and AST enzyme kinetics differ

• CK peaks fast, has a shorter half life, and normalizes quickly

• AST peaks slower, has a longer half life, and takes a lot longer to normalize

You draw a blood sample 48 hours after some incident, and the CK is normal but the AST is elevated. Why is this not liver disease?

This could still be a muscle injury and the CK may have normalized already

Parameters looked at to evaluate liver injury or cholestasis

Liver enzymes

Parameters looked at to evaluate liver failure

Liver function tests → liver products

Cholestasis

Blockage of bile flow

Large animal leakage enzymes

• AST

• SDH

• SLDH

• LDH

Large animal leakage enzyme that is the best (liver specific)

SDH

Large animal leakage enzyme that elevates with liver and muscle damage

AST and LDH

Inducible liver enzymes

ALP and GGT

For which species is ALP most specific for cholestasis

Dogs and cats

For which species is GGT most specific for cholestasis

All species, but only good one for horses and cattle

T/F: the severity of enzyme elevation can be a prognostic indicator

False

Reasons other than cholestasis that will increase both ALP and GGT in all animals

Colostrum intake

Reasons other than cholestasis that will increase both ALP and GGT in dogs ONLY

Corticosteroids (endogenous or exogenous) and anticonvulsants

Reasons other than cholestasis that will increase ALP in all animals

• Osteoblastic activity

• Cancer

• Endocrine/metabolic conditions

Why is interpreting ALP in cats different

They have less ALP, so any increase is significant

Reasons other than cholestasis that will increase ALP in cats

Hyperthyroidism

Why is interpreting GGT in cats different

GGT is usually more sensitive for cholestasis except for when it is caused by hepatic lipidosis