Reviewing the chemistry panel: Liver cases (Proceedings)

The Serum Chemistry Profile

5 Components:

      1. Electrolytes / Acid-Base

      2. Kidney

      3. Glucose

      4. Proteins

      5. Muscle enzymes

      6. Liver parameters

Liver Components

      1. Enzymes

          • SDH

          • AST

          • GGT

          • SAP

      2. Functional components

          • BUN

          • Glucose

          • Albumin

          • Iv. Bilirubin

Enzymes

      Hepatocellular enzymes:

1. SDH

     • Short half-life

     • Cytosolic (means necrosis present)

     • Liver specific

2. AST

     • Intermediate half-life

     • Cytosolic (means necrosis present)

     • Not specific: also from muscle

Biliary:

1. GGT

          • Very long half-life (several days) and upregulated

          • Secreted (It means the ducts have been irritated/inflamed, Increase does not mean necrosis of cells)

          • Biliary-specific (nearly...also found in pancreatic ducts)

2. SAP (serum alkaline phosphatase)

          • Intermediate half-life

          • Secreted (Increase means cells are irritated, not necessarily necrotic)

          • Found in several other tissues:

          • SAP also from bone, placenta, inflammatory cells...

Clinical Relevance

          • SDH tells what is on-going (current status)

          • GGT stays increased for weeks after insult

          • SDH and GGT confer specificity

               o indicate liver/biliary disease

          • SDH and AST indicate hepatocellular necrosis

          • GGT and SAP indicate biliary disease

Functional Indicators in the Chem Panel

These analytes are made by the liver:

Liver dysfunction / failure:

          • BUN ↓ - except neonate

          • Glucose ↓ – late finding

          • Albumin ↓ – late finding; < 20 % of cases

          • Cholesterol ↓

Bilirubin

          • Indirect (unconjugated)

          • Direct (conjugated)

One or both increase with liver disease

Direct fraction = 25 % of the total BR strong evidence of biliary disease

General Guidelines in Interpretation

1. Relatively greater increases of biliary enzymes (GGT, SAP) over hepatocellular enzymes (SDH, AST) indicate primary biliary disease:

Examples include:

          • Cholangitis/cholangiohepatitis

          • Cholelithiasis or other biliary obstruction, including GI displacements

          • Pyrrolizidine Alkaloid Toxicity

          • Biliary tumors

2. Relatively greater increases of hepatocellular enzymes over biliary enzymes indicate primary hepatocyte disease:

Hepatitis/ cholangiohepatitis

Liver Toxicities

          • Theiler's disease (serum hepatitis) in adults

          • Tyzzer's disease in foals

          • Carcinomas

General Guidelines

3. Relatively equal increases in biliary and hepatocellular enzymes:

          • Variations of all of the above differential diagnoses

          • Gut disease – secondary to colic or colitis

          • Hyperlipemia

          • Other toxicities

Treatment Guidelines

Liver Disease

1. IV fluid therapy

Optimal crystalloids: Normosol R or Plasma-Lyte 148

          • Contain acetate and gluconate, no lactate which is primarily liver metabolized

          • Alkalinizing compared to 0.9% saline

          • Supplement fluids with potassium!

               o Aids in preventing hyperammonemia

               o 20 mEq/L KCl even if potassium normal

      PCV may remain elevated due to primary polycythemia

2. Nutritional Support

          • Dextrose in fluids: 0.5-2 mg/kg/min

               o Example: 1.5-5 % in 1 liter/h

          • B complex vitamins:

               o May be deficient

               › Aid in glucose metabolism

               › Neuroprotective

               › 1 cc per 100 lb in fluids/ day

          • Parenteral nutrition- be careful of excessive amino acids if hyperammonemic

          • If eating:

               o Beet pulp, grass hay and grain

               › BCAA

               › Be careful tubing horses with liver failure! – bloody nose

3. Avoid sedation, especially diazepam

4. Low dose flunixin meglumine (Banamine)

          • For endotoxemia

          • For inflammation

5. Plasma transfusion if coagulopathy present

6. Antioxidants - vitamin E, selenium

7. Treatment of hepatoencephalopathy:

     • Lactulose 0.2-0.25 ml/kg PO q 8 h

               o Decreases ammonia concentrations in gut and therefore plasma through ion trapping

          • If neurologic signs present:

               o Mannitol or DMSO

Conclusion

1. Increases in liver enzymes alone signify liver disease, not necessarily failure

          • GGT and SAP indicate primary biliary diseases

               o Cholangiohepatitis

               o Cholelithiasis

               o PA toxicity

          • SDH and AST indicate primary hepatocellular disease

               o Theiler's

               o Tyzzer's

               o Hepatitis

          • Increases in both

               o Any of above diseases

               o Secondary to GI disease

               o Hyperlipemia

Conclusion

2. Liver failure is suggested by

          • Low BUN, glucose, albumin; high BR

3. Remember colic and diarrhea cases can have secondary increases in liver enzymes

Colon displacements

          • Colon torsions

          • Enteritis