Liver Function PDF

# LABORATORY MEASUREMENT OF AMMONIA - **Specimen:** Chilled heparinized EDTA arterial plasma - **Sample:** Centrifuged at 0-4°C within 20 minutes of collection and plasma is removed - **Avoid:** Cigarette smoking for several hours prior to test (can cause false increase) ## Methods: 1. **Chemica...

# LABORATORY MEASUREMENT OF AMMONIA - **Specimen:** Chilled heparinized EDTA arterial plasma - **Sample:** Centrifuged at 0-4°C within 20 minutes of collection and plasma is removed - **Avoid:** Cigarette smoking for several hours prior to test (can cause false increase) ## Methods: 1. **Chemical Methods** - **ISE - Potentiometry with gas sensing electrode:** Antibiotics: Monactin Nonactin - **Spectrophotometry:** Ammonia + bromphenol blue → blue dye - **Berthelot Reaction:** Uses phenol and sodium hypochlorite, (+) blue indophenol compound - **Nesslerization Reaction:** Utilizes diiodides (HgI2, KI + gumghatti), (+) yellow 2. **Enzymatic - GLD Method:** - Uses diiodides (HgI2, KI + gumghatti) - Decrease in absorbance of NADPH at 340nm # LIVER FUNCTION ## LIVER ANATOMY AND PHYSIOLOGY - **Largest internal organ** - **Serves as gatekeeper of the body** **Complex organ responsible for many metabolic functions:** - **Reddish brown** and located under the diaphragm, in the right upper quadrant of the abdomen - **Has abundant blood supply:** - Receiving approximately **1500ml/min** from two major vessels: - **Hepatic Artery** (Branch of the aorta that provides most of the oxygen requirement, contributes 20% of the blood supply) - **Portal Vein:** Drains the gastrointestinal tract and spleen (transports materials from the intestines to the liver, drains from general circulation) - **Metabolic activity of the liver:** Takes place in the parenchymal cells (constitute 80% of the organ mass): - The liver also contains **Kupffer cells** (reticuloendothelial) and **stellate cells** (major cell type responsible for fibrosis) - **Total loss of liver functions** leads to death due to **hypoglycemia** within 24 hours **Each liver lobule:** Composed of six-sided functional unit **Components of the liver lobule:** 1. Branches of hepatic portal vein and hepatic artery 2. **Central Vein** 3. **Sinusoids** 4. Hepatocytes & Kupffer cells 5. **Bile canaliculi** 6. **Bile ducts** # LIVER FUNCTIONS ## A. DETOXIFICATION - **First Pass Effect:** Everything absorbed by the body passes through the liver. - **Phagocytosis by Kupffer cells** - **Metabolism and excretion:** Drugs & foreign compounds - **Production of Urea:** From ammonia. Conjugated bilirubin. - **Other molecules** that are less toxic than their parent compounds ## B. SECRETION / EXCRETION - Metabolism (conjugation and excretion of bilirubin). - Synthesis of bile salts and bile acids (breaks down fats). ## C. SYNTHESIS / METABOLISM 1. **Carbohydrates:** Glucose converted to glycogen, stored in the liver and later reconverted to glucose as necessary. Liver failures cause hypoglycemia within 24 hours. 2. **Fats:** Endogenous triglycerides, phospholipids, and cholesterol. 3. **Lipoproteins:** High- and low-density lipoproteins 4. **Ketone Bodies:** By-product of gluconeogenesis 5. **Proteins:** - Albumin (12g/day) - Majority of alpha and beta globulins - All blood clotting factors except FVII (synthesized by vascular endothelium) 6. **Hormones:** - Transamination (AST, ALT), Deamination - Somatomedin (mediates the activity of growth hormone) and angiotensin ## D. STORAGE - Fat-soluble and water-soluble vitamins, glycogen, and iron ## BILIRUBIN - Forms a complex with albumin for transport to the liver. - Conjugated in the endoplasmic reticulum with 2 molecules of glucuronic acid to form bilirubin diglucuronide (conjugated bilirubin or B2). - The reaction is catalyzed by UDP Glucuronyl Transferase (UDGPT) | | Total bilirubin | Conjugated bilirubin | Unconjugated bilirubin | |------------|----------------|----------------------|-------------------------| | **RV:** | 0.2-1.0 mg/dL | 0.0-0.2 mg/dL | 0.2-0.8 mg/dL | | **µmol/L:** | 3 - 17 µmol/L | 0 - 3 µmol/L | 3 - 14 µmol/L | **BILIRUBIN 1** - Unconjugated bilirubin - Water-insoluble - Non-polar - Indirect reacting - Hemobilirubin - Free bilirubin/Unbound - Pre-hepatic - Not in urine - High affinity for brain tissue **BILIRUBIN 2** - Conjugated bilirubin - Water-soluble - Polar - Directly reacting - Cholebilirubin - Bound - Post hepatic / Obstructive - Present - Low affinity for brain tissue # LIVER DISORDERS - **The most common disease processes affecting the liver are:** - **Hepatitis:** Damage to and destruction of liver cells; may be acute or chronic or a combination of both. - **Cirrhosis:** A process in which death of liver cells with regeneration leads to fibrosis, scarring and destruction of the normal liver architecture. - **Primary biliary cirrhosis:** Progressive autoimmune disease characterized by destruction of intrahepatic bile ducts, presence of antimitochondrial antibodies in the plasma. - **Tumors:** Both primary, but more frequently, secondary. For example, metastases from cancers of the large bowel, stomach, and bronchus. ## JAUNDICE / ICTERUS - **Yellowish pigmentation of the skin, mucous membrane and sclera of the eyes due to hyperbilirubinemia.** - **Not apparent until bilirubin exceeds 3.0 – 5.0 mg/dL (overt jaundice)** ## CLASSES OF JAUNDICE ### Pre-Hepatic: Hemolytic / Retention Jaundice - **Causes:** - Excessive destruction of RBCs - Free bilirubin is elevated due to HDN or erythroblastosis fetalis and malaria - Hepatic uptake is decreased: Prolonged fasting and intake of drugs. ### Hepatic - **Causes:** - Severe damage to the hepatocytes due to microorganisms or alcohol - Starvation and certain medications - Hepatitis and cirrhosis - Parasitism (Fasciola hepatica) ### Bilirubin Conjunction Decreased: - **Physiological neonatal jaundice** - **Gilbert’s Disease** - **Crigler-Najjar syndrome** - UDGPT is only 30% functional - Defect in the transport protein ligandin - **Lucey-Driscoll syndrome** - UDGPT deficiency - **Conjugation deficit** - Circulating inhibitor of conjugation ### Impairment of Hepatic Excretion (Acquired Disorders) - **Dubin-Johnson Syndrome** - **Excretion deficit** - Presence of delta bilirubin, dark stained granules (lipofuscin) in liver biopsy. - **Rotor Syndrome** - Uptake/Transport deficit - Reduced/defective ligandin - Possibly viral in origin ### Post-Hepatic: Regurgitative / Obstructive / Cholestatic Jaundice - **Causes:** - Obstruction of the biliary flow - Intra-hepatic cholestasis - Obstruction of the extra-hepatic biliary tree - Cholelithiasis, or gallstones - Strictures, spasms, atresia and microorganisms - Cancer of the head of the pancreas - Ascaris lumbricoides infection ### Neonatal Jaundice - **Buildup of unconjugated bilirubin.** - **Noted 2-3 days of neonatal life, rarely rises greater than 5 mg/day (peaks at 4-5 days) - **Most common cause is HDN** - **Poorly developed blood brain barrier allowing B1 to cause damage to central nervous system - Kernicterus (B1 > 20 mg/dL)** - **Treatment:** Photo therapy | | Total Bilirubin | B1 | B2 | Urine Bilirubin | Urine Urobilinogen | Stool | |------------|----------------|-----|-----|----------------|--------------------|-------| | **Pre-Hepatic** | ↑ | ↑ | N | - | - | Brown | | **Hepatic** | ↑ | ↑ | ↑/N | Variable | N | Pale/Brown | | **Post-Hepatic** | ↑ | N | ↑ | + | N | Clay | - **Reye's Syndrome:** Hepatic destruction following recovery from viral infection and aspirin ingestion in children, wherein the patient develops neurologic abnormalities due to accumulation of *ammonia* in the CNS. - **Non-inflammatory hepatic encephalopathy and fatty liver degeneration** ## BILIRUBIN DETERMINATION - **Specimen:** Fasting serum - Protect from light (light decreases bilirubin by 30-50% per hour) - Avoid hemolysis (falsely decreased) - Lipemia (falsely increased) - **Principle:** Van den Berg reaction - diazotization of bilirubin to produce azobilirubin ## Diazo reagent: - 0.1% Sulfanilie acid + HCl - 0.5% Sodium nitrite - **Unconjugated bilirubin (B1):** Reacts with Diazo reagent with an accelerator. - **Conjugated bilirubin (B2):** Reacts directly with Diazo reagent. - **Delta bilirubin:** B2 bound to albumin and behaves like conjugated. ## Types: - **Direct Method:** No coupling accelerator; only direct bilirubin is determined, B2 reacts with the reagent. - **Indirect Method:** A coupling accelerator is added to make both B1 and B2 react with the reagent **Preferred Spec:** Serum (plasma, protein interferences) | | Evelyn-Malloy | Jendrassik-Grof | |------------------|--------------------------------------------------|---------------------------------------| | **Accelerator** | 50% Methanol | Caffeine-Benzoate | | **Stopper** | - | Ascorbic acid | | **pH** | Acidic | Alkaline tartrate / Sodium acetate buffer | | **End Color** | Red-Purple | Pink - Blue | | **Absorbance Peak** | 560nm | 600 nm | - **More Sensitive** - **Reference Method:** Derived from Evelyn-Malloy