Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (172 page)

These studies are of proven benefit in determining the proximate etiologies in the patient presenting with jaundice. With this approach, the clinician can confidently assign probabilities to the major categories that most frequently account for jaundice.

   The first step is to determine the total bilirubin and the bilirubin fractions. This allows the clinician to determine whether the problem is due to an excess production or impaired conjugation (indirect/unconjugated predominant) versus impaired excretion (direct/conjugated predominant).

   ALP elevations out of proportion to the hepatic transaminases would favor extrahepatic or intrahepatic cholestasis.

   Hepatic transaminase elevations out of proportion to the alkaline phosphatase favor hepatocellular etiologies.

   The CBC can be extremely useful. The most important points include the interpretation of or for

   Anemia (hemolysis, bleeding) (see Chapter
10
, Hematologic Disorders)

   Mean corpuscular volume (microcytosis suggests iron deficiency; round macrocytosis suggests chronic liver disease or ineffective erythropoiesis; GI malignancy)

   Thrombocytopenia (sequestration in portal hypertension, sepsis, autoimmune disease, bone marrow suppression [alcohol])

   Reticulocytosis (hemolysis) (see Chapter
10
, Hematologic Disorders)

   Urinalysis provides information about bilirubinuria and urobilinogen. In reality, data from urinalysis add little incremental benefit to the decisionmaking process.

   The presence of urobilinogen eliminates the possibility of complete biliary tract obstruction. That is, bile has entered the intestine, where it undergoes enterohepatic metabolism.

   The presence of bilirubinuria, on the other hand, suggests that conjugation is taking place.

   Coagulation studies are useful in two areas.