Pearls
- CBC changes that may be seen with hepatobiliary disease:
- Mild microcytosis with or without mild nonregenerative anemia and hypochromic RBCs may be seen with PSSs. The CBC findings can provide important clues.
- Cats with chronic liver disease may have significant red cell pathology in the form of unclassified poikilocytosis and echinoelliptocytes.
- Inflammatory leukograms may be seen in cholangiohepatitis and cholecystitis.
- Icteric plasma may be seen.
- Hypoproteinemia may be present if hepatic pathology results in hepatic dysfunction.
- Biochemical changes that may be seen with hepatobiliary disease:
- AST, ALT, SDH, and GLDH are leakage enzymes that can indicate hepatocellular injury. AST and occasionally ALT can also be released from myocytes, so it is useful to evaluate these in relation to CK, a muscle-specific enzyme. ALT is used in small animals; SDH, GLDH, or both replace ALT in large animals. There can be significant hepatocellular injury and increases in serum activity of these enzymes in the absence of histologic lesions. The degree of elevation does not indicate the extent of the lesion or the severity (i.e. the damage can be localized or diffuse, reversible or irreversible). Monitoring the enzyme activities over time can be very useful prognostically. For example, a dog with chronic hepatitis might have only a mild elevation in ALT activity, but if this persists for years, then a cirrhotic, dysfunctional liver may be the end result. Another animal could have a massive increase in ALT activity due to trauma or transient hypoxia associated with shock or blood loss. The enzyme activity may return to within the RI relatively quickly and the patient suffer no long term effects whatsoever.
- GGT and ALP are indicators of cholestasis. Both are used in small animals; only GGT is useful in large animals. Young animals have mild elevations in ALP activity due to the bone isoform; this subsides as growth slows and stops. States of increased bone turnover such as healing fracture, osteomyelitis, or osteosarcoma can also increase ALP release. GGT is absorbed from colostrum in many neonatal, nursing animals. High levels of endogenous or exogenous steroids can cause increased activities of ALT, ALP, and GGT in dogs. There may be mild enzyme increases in horses with equine PPID (see Chapter 10: Endocrine System).
- Bilirubin elevation often accompanies cholestatic liver disease. Hyperbilirubinemia is occasionally seen in anorexic horses, cattle, and cats and in animals with septicemia.
- Urea, glucose, cholesterol, and albumin concentrations can provide clues as to hepatic function. Low concentrations may accompany liver failure. Animals with PSSs may have no or only mild elevations in ALT, ALP, and GGT activity, but low urea, albumin +/- cholesterol +/- glucose.
- DON’T RULE OUT LIVER DISEASE IF HEPATIC ENZYMES ARE NORMAL.
- DON’T DIAGNOSE LIVER DISEASE BASED ON INCREASED HEPATIC ENZYME ACTIVITIES ALONE.
- Occasionally, both albumin and globulins are decreased in hepatic dysfunction resulting in a normal albumin to globulin ratio. Several of the globulins, other than immunoglobulins, are produced in the liver, and this is a possible explanation for this finding.
- Specific liver function tests are often done to confirm hepatic dysfunction. These include bile acids and ammonia tolerance tests.
- Increased bile acids may reflect cholestasis, portal vascular anomaly (such as a PSS), or decreased functional hepatic mass. There is no diagnostic value in performing bile acid testing in a hyperbilirubinemic patient.
- Some animals with liver disease are polyuric and polydipsic due to a low urea and loss of concentration gradient across the renal medulla. These animals may have hyposthenuria.
- Animals with hepatic shunts (congenital or acquired) may have ammonium urate crystals in their urine, indicating impaired urea synthesis and a need to excrete excess ammonia.
definition
Urine specific gravity <1.007, reflects dilution of the urine by the kidneys.
