Chapter 16-1.pdf

Chapter 16 Introduction to laboratory diagnostics Laboratory Tests  Laboratory tests assist healthcare providers in evaluating client health and making informed decisions.  Tests can be ordered for screening, evaluation of drug effectiveness, diagnosis confirmation, or rul...

Chapter 16 Introduction to laboratory diagnostics Laboratory Tests  Laboratory tests assist healthcare providers in evaluating client health and making informed decisions.  Tests can be ordered for screening, evaluation of drug effectiveness, diagnosis confirmation, or ruling out clinical issues.  Lab results influence clinical decision-making and client care plans.  Comprehending laboratory terminology is essential for safe and efficient care. Normal Ranges vs. Reference Ranges  Normal ranges are determined by analyzing results from a large group of healthy individuals.  Ranges can vary depending on factors like age and gender.  For example, males have a higher hemoglobin level than females. Critical Values  Critical values represent dangerously abnormal results requiring immediate action to prevent life-threatening situations. Post-Test Considerations  Post-test assessments may be necessary depending on the results obtained. 16-1. CHEMISTRY TESTS  Chemistry Tests  Chemistry tests measure chemical components in bodily fluids and tissues to identify abnormalities.  Blood and urine are commonly used specimens. * All lab values are shown in SI format. To ensure accuracy and to maintain optimal level of care for individuals receiving any lab tests or specimen collection, please refer to your workplace policies and procedures manual or contact the laboratory. Ammonia (AMM, NH3) Normal Range 6–47 mcmol/L Indications Used to diagnose severe liver diseases. Test Explanation Measures the amount of ammonia in the blood. Ammonia in the body is created by the breakdown of protein. The liver converts ammonia to urea, which is excreted as urine in the kidneys. Blood Tube: Green Purpose Check liver function. Check success of treatment for severe liver disease (e.g., cirrhosis). Check levels in a person receiving total parenteral nutrition. Interfering Factors Smoking. Eating high-protein or low-protein diet. Drugs that increase blood ammonia (e.g., Loop diuretics, narcotics, thiazides, alcohol). Drugs that decrease blood ammonia (e.g., broad spectrum  antibiotics, levodopa, potassium salts) Strenuous exercise before test. Results and Lower Higher Significance Essential or Liver disease (cirrhosis or malignant hepatitis) hypertension Reye syndrome Heart failure Kidney failure Severe bleeding from stomach or intestines Bilirubin Reference Range Bilirubin is a tetrapyrrole and a breakdown product of heme catabolism. Most bilirubin (70%-90%) is derived from hemoglobin degradation and, to a lesser extent, from other hemo proteins. In the serum, bilirubin is usually measured as both direct bilirubin (DBil) and total-value bilirubin (TBil). Direct bilirubin correlates with conjugated bilirubin but tends to overestimate actual conjugated bilirubin, as it includes both the conjugated bilirubin and bilirubin covalently bound to albumin (delta-bilirubin). Indirect bilirubin correlates with unconjugated bilirubin but tends to underestimate unconjugated bilirubin, as a portion of the unconjugated bilirubin reacts with diazosulfanilic acid, producing azobilirubin, which is measured as direct bilirubin. Normal findings Adult/elderly/child:  Total bilirubin: 0.3-1.0 mg/dL or 5.1-17 μmol/L (SI units)  Indirect bilirubin: 0.2-0.8 mg/dL or 3.4-12.0 μmol/L (SI units)  Direct bilirubin: 0.1-0.3 mg/dL or 1.7-5.1 μmol/L (SI units) Newborn:  Total bilirubin: 1.0-12.0 mg/dL or 17.1-205 μmol/L (SI units) Possible critical values Total bilirubin :  Adult: >12 mg/dL  Newborn: >15 mg/dL Interpretation Elevated bilirubin levels (>2.5-3 mg/dL) cause jaundice and can be classified into different anatomical sites of pathology: prehepatic (increased bilirubin production), hepatic (liver dysfunction), or posthepatic (duct obstruction). Another way of approaching hyperbilirubinemia is to divide it into two general categories: unconjugated hyperbilirubinemia and conjugated hyperbilirubinemia. The prevalence of hyperbilirubinemia varies depending on the cause. Conjugated hyperbilirubinemia is common in individuals with hepatocellular injuries and biliary obstruction and is also common in persons with sepsis. Some of the inherited diseases associated with conjugated hyperbilirubinemia are estimated to affect 4%-13% of the US population, while Dubin-Johnson syndrome (DJS) is rare except in Iranian Jews, in whom the prevalence is about 1 in 1300. Unconjugated hyperbilirubinemia is common in newborns and is likely related to a higher hematocrit (50%-60%) with increased cell turnover (the average lifespan of a red cell is about 85 days in the neonate) combined with decreased uridine diphosphoglucuronate glucuronosyltransferase (UGT) activity. One study found that up to 6.1% of neonates had unconjugated bilirubin levels higher than 12.9 mg/dL. Breastfeeding was more common in neonates with higher levels of unconjugated hyperbilirubin. Causes of unconjugated and conjugated hyperbilirubinemia are discussed below. Unconjugated hyperbilirubinemia Increased bilirubin production via hemolysis and dyserythropoiesis Increased destruction of red blood cells (hemolysis) can increase the production of unconjugated bilirubin. Ineffective erythropoiesis is another cause of increased unconjugated bilirubin production that involves rapid hemoglobin turnover and destruction of a fraction of developing erythroid cells within the bone marrow. The percentage of bilirubin production from this mechanism can reach 70% in dyserythropoiesis disorders such as thalassemia major, megaloblastic anemia, congenital erythropoietic porphyria, and lead poisoning. If the production of unconjugated bilirubin is prolonged, it can precipitate bilirubin salts, leading to the formation of gallstones. Treatment is aimed at managing the underlying disease process. Decreased hepatic clearance Decreased hepatic clearance may be caused by congestive heart failure, cirrhosis/portosystemic shunts, and/or certain drugs. Impaired delivery of bilirubin to the liver in conditions such as congestive heart failure or in patients with portosystemic shunts can decrease the hepatic bilirubin uptake by the liver. Occasionally, cirrhosis can cause unconjugated hyperbilirubinemia, as hepatic fibrosis leads to capillarization of the sinusoids, causing decreased bilirubin uptake by hepatocytes. Treatment includes treating the underlying condition. Drugs such as rifamycin, rifampin, probenecid, flavaspidic acid, and bunamiodyl inhibit bilirubin uptake, which can be reversed upon cessation of these drugs. Defective bilirubin conjugation Inherited disorders associated with defective bilirubin conjugation include Crigler-Najjar syndrome types I and II and Gilbert syndrome. Ethinyl estradiol and hyperthyroidism are also associated with defective bilirubin conjugation. Crigler-Najjar syndrome is a very rare autosomal-recessive disorder caused by an alteration of the coding region of the gene responsible for producing bilirubin-UGT, which normally conjugates bilirubin. This results in the production of an abnormal protein, which can cause a complete or near loss of function (type I) or a very low level of function (type II). Individuals with type I Crigler-Najjar syndrome usually present with very high levels of unconjugated hyperbilirubin at birth, resulting in kernicterus. Treatment involves emergent plasma exchange to treat kernicterus followed by regular phototherapy. If left  untreated, type I is fatal by about age two years. Patients with type II may not require any therapy or may be treated with phenobarbital, which can induce the expression of UGT. Patients with type I do not respond to phenobarbital, as the mutation is a loss-of-function mutation. Gilbert syndrome has also decreased UGT activity (typically 10%-33% of normal), but results from a mutation in the promoter region and therefore decreased levels of a normal protein are produced. Gilbert syndrome is completely benign and has no effect on life expectancy. Therefore, management is centered on reassurance, and no medical therapy is indicated. Multifactorial etiologies Chronic hepatitis is also associated with unconjugated hyperbilirubinemia. Conjugated hyperbilirubinemia Hepatitis Hepatitis (viral, alcoholic, autoimmune) is associated with conjugated hyperbilirubinemia Liver infiltration The following diseases may lead to liver infiltration, potentially resulting in conjugated hyperbilirubinemia:  Amyloidosis  Lymphoma  Sarcoidosis  Tuberculosis Biliary obstruction Biliary obstruction may be caused by the following:  Malignancies (cholangiocarcinoma, pancreatic cancer)  Chronic pancreatitis (pseudocysts, stricture)  Acute pancreatitis  Primary sclerosing cholangitis (PSC; discussed further below)  Choledocholithiasis  Postsurgical biliary strictures  Choledochal cysts (discussed further below)  Biliary atresia  PSC is characterized by progressive inflammation and scarring of the bile ducts. It is thought to be autoimmune in nature and is often associated with inflammatory bowel disease (IBD; ulcerative colitis or Crohn colitis). The disease course is independent of that of IBD. Treatment is mainly supportive. PSC is associated with an increased risk for cholangiocarcinoma. Liver transplant is the treatment used when PSC results in end-stage liver disease. Congenital cystic dilations of the bile duct are typically associated with intermittent abdominal pain, jaundice, and right upper quadrant mass. These are important to recognize owing to the risk of malignancy. Treatment is mostly surgical depending on the type of choledochal cysts. Infections Infections associated with conjugated hyperbilirubinemia include the following:  CMV  Parasitic infections  Cholangitis  Cholecystitis Inherited disorders DJS is an autosomal-recessive disease characterized by a mutation in the gene responsible for the human canalicular multispecific organic anion transporter (cMOAT) protein, also known as the multidrug resistance protein 2 (MRP2). This mutation results in the impaired transport of nonbile salt organic anions across the canalicular membrane of the hepatocyte, resulting in conjugated hyperbilirubinemia Rotor syndrome is very similar to DJS. It is also autosomal recessive, although the exact genetic defect has yet to be determined. Like DJS, Rotor syndrome is benign and requires no specific therapy. DJS can be differentiated from Rotor syndrome in that DJS is characterized by normal urinary levels of coproporphyrin, as opposed to Rotor syndrome, which is characterized by high levels. Additionally, DJS is associated with black pigmentation of the liver, whereas Rotor syndrome is not. Primary biliary cirrhosis Primary biliary cirrhosis is an autoimmune disease of the liver involving progressive destruction of small intrahepatic ducts. It is much more common in females and usually  presents with pruritus, fatigue, and jaundice. It results in end-stage liver disease. Treatment with ursodiol slows the disease progression. Like PSC, liver transplantation is the treatment of choice whenever cirrhosis sets in. Benign recurrent intrahepatic cholestasis Benign recurrent intrahepatic cholestasis (BRIC) is a rare autosomal-recessive or sporadic disorder with recurrent episodes of intense pruritus and jaundice that resolves spontaneously without significant liver damage. AIDS cholangiopathy AIDS cholangiopathy is a syndrome of biliary obstruction thought to result from infection- induced strictures of the biliary tract. The most common organism associated with AIDS cholangiopathy is Cryptosporidium parvum, although other organisms have also been implicated. Total parenteral nutrition The etiology of total parenteral nutrition (TPN)–induced cholestasis is not completely understood and is likely multifactorial, involving excessive calories with deficiencies in micronutrients and possibly bacterial translocation from the gut. Wilson disease Wilson disease is an autosomal-recessive disease involving copper deposition in multiple tissues, including the brain and liver. Symptoms usually present by about age20 years, although cases in older people have been described. The ceruloplasmin levels are usually reduced. Cupper chelation is used for treatment. Drugs Many drugs can cause liver injury that results in hyperbilirubinemia associated with elevated liver enzymes. Isolated elevated bilirubin levels caused by drugs is much less common, but some drugs are known to do this, as follows:  Isoniazid  Chlorpromazine  Erythromycin  Anabolic steroids Other Other causes of conjugated hyperbilirubinemia include the following:  Sepsis  Shock  Hemochromatosis Collection and Panels Bilirubin testing involves withdrawal of 0.5 mL of plasma (green-top [heparin] tube) or 0.7 mL of serum (red-top tube or gold-top 7-mL SST tube). Description Bilirubin is a tetrapyrrole and a breakdown product of heme catabolism. Most bilirubin (70%-90%) is derived from hemoglobin degradation and, to a lesser extent, from other hemo proteins. In its unconjugated form, bilirubin is water-insoluble and binds avidly to tissues such as brain, sclera, and mucous membranes. This is minimized by its binding to albumin in the plasma, which keeps it confined to the vascular space. The glomerular apparatus in the kidneys does not filter it. In the liver, the albumin-bilirubin complex dissociates, and it is taken up by the hepatocytes. It is conjugated via uridine diphosphoglucuronate glucuronosyltransferase (UGT) into its water-soluble form. Overproduction of bilirubin (hemolysis) or defects in uptake and conjugation can result in unconjugated hyperbilirubinemia. Bilirubin diglucuronide is the predominant conjugated form (80%-85%). Conjugated bilirubin is excreted into bile and delivered to the small intestine. Medical conditions and drugs that interfere with the excretion result in conjugated hyperbilirubinemia. Intestinal bacteria convert bilirubin into several urobilinogens. A portion of the urobilinogens are then reabsorbed by the intestine and circulated back to the liver in a process called enterohepatic circulation. A small portion of urobilinogen is excreted from the body through the urine, while most is excreted in the stool. They give urine and stool their characteristic yellow and brown colors, respectively. In the event of absent urobilinogens in the stool and urine, the feces turn clay in color and the urine assumes a dark discoloration. For more information concerning hyperbilirubinemia, see Unconjugated Hyperbilirubinemia and/or Conjugated Hyperbilirubinemia.  Indications/Applications Bilirubin testing is indicated upon signs of abnormal liver function. Signs include the following:  Jaundice  History of alcoholism  Suspected drug toxicity  Exposure to hepatitis viruses Bilirubin testing is also performed in newborns with jaundice. Bilirubin testing is typically performed along with other laboratory tests, such as alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase. Considerations Jaundice is the most common symptom of hyperbilirubinemia and is typically seen once total bilirubin levels approach 2-3 mg/dL. The earliest anatomic sites where jaundice can be seen are under the tongue and in the sclera (scleral icterus). Asymptomatic jaundice is common in ineffective erythropoiesis or hemolysis. In Gilbert syndrome, unconjugated bilirubin levels are mildly elevated at baseline but increase in the state of illness, physical or emotional stress, and in fasting. Dark urine is a primary presentation of conjugated hyperbilirubinemia, but not unconjugated hyperbilirubinemia, as it is water-insoluble and thus not excreted in the urine. Signs of ascites, splenomegaly, spider angiomata, and gynecomastia are typical of chronic liver disease. The presentation of neurological symptoms can indicate alcohol use. Tumors and an enlarged gallbladder may be evident as palpable abdominal masses. Several physical clues may suggest certain disorders, such as Kayser-Fleischer ring in Wilson disease or hyperpigmentation in hemochromatosis. Amylase (AMY) Normal Serum Amylase Urine Amylase Range