TESTS OF HEPATIC FUNCTION
Although the liver performs a great variety of presumably testable functions, it has proved difficult to devise a test that is simple, cheap, reproducible, and noninvasive and that accurately reflects hepatic capacity for all functions. Instead,currently available tests of liver function are indirect, static measurements of serum levels of compounds that are synthesized, metabolized, and/or excreted by the liver. In interpreting these tests, it is important to remember that the liver has a large reserve capacity, and therefore “function” tests may remain relatively normal until liver dysfunction is severe. Table 43-2 outlines the most available and useful liver function tests. The serum albumin level and prothrombin time both reflect the hepatic capacity for protein synthesis, although changes in these proteins are not specific for liver disease. The prothrombin time responds rapidly to altered hepatic function because the serum half-lives of Factors II and VII are short (hours). In contrast, the serum half-life of albumin is 14 to 20 days, and serum levels fall only with prolonged, severe liver dysfunction.
Serum bile acid levels, particularly when measured two hours after a meal, have proved to be the most sensitive test of liver disease, and this is due to the high efficiency with which the liver normally extracts bile acids from portal blood. Small changes in hepatic blood flow, portosystemic shunting, or liver function all result in a substantial elevation of serum bile acid levels, while terminal ileal dysfunction (e.g., Crohn’s disease] leads to fecal loss of bile acids and decreased serum levels. Although exquisitely sensitive, bile acid levels are nonspecific and fail to reflect accurately overall liver function.
The 14C-aminopyrine breath test was originally developed as a true test of liver function. It measures the rate at which the liver metabolizes 14C-labeled aminopyrine to 14C02, which is collected and measured in exhaled breath. This test is performed in some academic centers and may be useful in following the progression of liver disease in an individual patient.
- Clinical Manifestations
- Sickle Cell Anemia (SS)
- Vitamin Dresistant Rickets
- NONPENETRATING TRAUMA
- PERICARDIAL DISEASES - ACUTE PERICARDITIS
- DIFFUSE LUNG DISEASE OF UNKNOWN ETIOLOGY
- Blood Chemistries
- Determination of Kidney Anatomy and Renal Blood Flow
- CLINICAL SYMPTOMS OF ESOPHAGEAL DISEASE
- CIRCULATORY PHYSIOLOGY
- HEART BLOCK
- Diet
- DEFINITION
- Sigmoidoscopy and Colonoscopy
- PERICARDIAL EFFUSIOH
- NORMAL ABSORPTION
- Endocrine and Other Considerations
- CARDIAC PACEMAKERS
- Liver Failure
- Complications of Dialysis
- CLINICAL APPROACH TO LIVER DISEASE
- Resuscitation
- Bleeding Diatheses
- CHROMIC PANCREATITIS
- CLINICAL MANIFESTATIONS OF MALABSORPTION
- TREATMENT OF MALABSORPTION
- EFFECTORS OF THE RESPIRATORY SYSTEM
- CLINICAL MANIFESTATIONS OF ENDSTAGE RENAL DISEASE
- Minimal Change Nephropathy
- Liddle’s Syndrome
- Renal Venous Occlusion
- PHYSIOLOGY OF THE CORONARY CIRCULATION
- GENERAL MANAGEMENT OF MYOCARDIAL INFARCTION
- Upper GI Bleeding
- PULMOIIARY FUNCTION EVALUATION