Capstone 51-70 Chemistry

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Capstone 51-70 Chemistry
2015-01-27 13:26:58
clinical chemistry

Capstone chemistry questions
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  1. Name three substances that are elevated in the blood with renal disease
    BUN (Blood Urea Nitrogen), creatinine, and uric acid
  2. What is urea?
    The end product of protein metabolism. It is synthesized in the liver from ammonia and carbon dioxide.
  3. What is the reference range for BUN?
    10-20 mg/dl
  4. Azotemia
    Refers to elevated levels of urea in the blood
  5. Why should tubes containing fluoride or citrate not be used when collecting blood for urea if analysis will be by the urease method?
    Fluoride and citrate inhibit urease.
  6. What is the formula for converting BUN to urea?
    Urea=BUN x 2.14
  7. Where is 98% of the body's creatine located?
    In muscles
  8. What is creatinine?
    The anhydride of creatine. Creatinine is formed from creatine by splitting out of water
  9. What reaction is used to measure creatinine?
    The Jaffe reaction using alkaline picrate. It is a nonspecific, but still clinically useful, method.
  10. What is the reference range for creatinine?
    0.5-1.5 mg/dl
  11. What is the significance of the BUN:creatinine ratio?
    It helps to determine the cause of an increased BUN. The normal ratio is approximately 10:1. Higher ratios are due to non-renal causes, such as a high protein diet, increased rate of protein catabolism, or decreased renal blood flow. With these conditions the BUN increased more than the creatinine. With renal disease, the BUN and creatinine increase proportionately.
  12. Calculate the BUN:creatinine ratio for a patient whose BUN is 45 mg/dl and whose creatinine is 2.1 mg/dl

    The normal ratio is 12-20. A ratio greater than 20 is suggestive of preener azotemia.
  13. What is the least variable nitrogenous constituent of blood?
    Creatinine, because it is related to muscle mass and is not affected by diet.
  14. What is an estimated glomerular filtration rate (GFR)?
    A calculation value based on serum creatinine and the patient's age, sex, and race. The National Kidney Disease Education Program (NKDEP) encourages reporting the estimated GFR along with the serum creatinine because it is a more sensitive indicator of kidney disease. At the time, the practice has not been widely adopted by clinical laboratories.
  15. What is uric acid?
    The end product of purine metabolism. The purines are adenosine and guanine, components of nucleic acids. Uric acid is increased with gout, renal disease, and conditions where there is high cellular turnover, such as leukemia.
  16. What reagent is commonly used to measure uric acid?
    Uricase. The preservative sodium fluoride must not be used to collect the blood sample because it destroys uricase. 
  17. What is the reference range for uric acid?
    3.0-7.0 mg/dl
  18. What may result from high levels of uric acid?
    Urate crystals may preciptate in joints and tissue. 
  19. Why must the pH of urine for a uric acid determination be adjusted to 7.5-8?
    To prevent precipitation of uric acid. Uric acid precipitates at acid pH.
  20. Where is ammonia formed?
    Mainly in the intestines from deamination of amino acids. It is converted to urea by the liver. 
  21. What is the reference range for ammonia?
    20-60 ug/dl
  22. When is ammonia elevated?
    With hepatic failure and Reye's syndrome. High levels are neurotoxic
  23. What is Reye's Syndrome?
    An acute, often fatal encephalopathy and fatty degeneration of the liver, seen primarily in children. It is associated with the use of aspirin in children with viral infections.
  24. What are two technical difficulties in preforming blood ammonia determinations?
    Levels increase rapidly after drawing, so the specimen must be placed on ice and the plasma separated from the cells promptly. Ammonia contamination from detergents, water, and smoke must be avoided. 
  25. Which amino acid is increased in the blood of patients with phenylketonuria (PKU)?
    Phenylalanine. PKU is due to a deficiency of the enzyme phenylalanine hydroxyls which catalyzes the conversion of phenylalanine to tyrosine. If untreated, PKU leads to mental retardation. The Guthrie bacterial inhibition assay is used for screening. HPLC is the reference method. 
  26. What may result if blood for PKU is drawn before 24 hours of age?
    False negatives.
  27. Which amino acids are increased in maple syrup urine disease (MSUD)?
    Leucine, isoleucine, and valine. The urine has a burnt sugar odor. MSUD leads to mental retardation and sometimes death. Many states require newborn screening. A modified Guthrie test is commonly used. MSUD can be treated by dietary modification if diagnosed early.
  28. What is bilirubin?
    The degradation product of heme. It is produced in the reticuloendothelial cells following breakdown of RBCs. 
  29. Which protein transports bilirubin in the blood?
  30. Name the two types of bilirubin.
    Direct and indirect. Indirect or unconjugated bilirubin in bilirubin en route to the liver. Once it goes through the liver it is known as direct bilirubin, conjugated bilirubin, or bilirubin diglucuronide.
  31. Explain what happens to bilirubin in the liver.
    It is conjugated with glucuronic acid by the enzyme uridyldiphosphate glucuronyl transferase (UDPG-T). Following conjugation, direct bilirubin is excreted into the intestine via the bile duct and is reduced by bacteria to urobilinogen. Urobilinogen is oxidized to urobilin and gives the normal color to stools. 
  32. What is the significance of clay-colored or light stools?
    It is a sign of obstruction of the bile duct. Urobilin is not being produced because bilirubin is not reaching the intestines. 
  33. Which substances related to bilirubin metabolism are normally found in the urine?
    Only urobilinogen. Bilirubin should not be present in urine.
  34. What urine abnormality is seen with complete obstruction of the biliary tract?
    Decreased urobilinogen.
  35. Which bilirubin fractions are analyzed in the laboratory?
    Total and direct. The indirect level is calculated by subtracting direct from total.
  36. Compare the solubility of direct and indirect bilirubin.
    Direct bilirubin is soluble in water; indirect bilirubin is not. Both are soluble in alcohol.
  37. Which form of bilirubin can be excreted in the urine?
    Only direct bilirubin.
  38. What common method for determination of bilirubin levels?
    Diazotization with sulfanilic acid. Bilirubin reacts with diazotized sulfanilic acid to produce azobilirubin.
  39. Name several accelerators that are used in the total bilirubin reaction.
    Alcohol or caffeine-benzoate-acetate can be used to make the indirect bilirubin soluble.
  40. Name a source of error that can decrease the level of bilirubin in a specimen 
    Exposure to light. Hemolysis will also cause a decreased level by the Jendrassik-Grof method.
  41. What is the normal range for total bilirubin in an adult?
    0.2-1.0 mg/dl. Conjugated (direct) bilirubin is <0.2 mg/dl.
  42. How do normal values for bilirubin in a newborn compare to those in an adult?
    Levels are higher in the newborn. The total bilirubin in a 3-5 day old full-term infant is 4-6 mg/dl; for a premature infant, 10-12 mg/dl
  43. What would cause an increase in total bilirubin with a normal concentration of direct bilirubin?
    Prehepatic jaundice, for example, hemolytic transfusion reaction, hemolytic anemia, or hemolytic disease of the newborn. 
  44. What causes physiologic jaundice of the newborn?
    Bilirubin metabolism in impaired because the newborn's immature liver doesn't produce the enzyme required for bilirubin conjugation. Phototherapy is used to reduce the level of bilirubin.
  45. In hemolytic disease of the newborn, which bilirubin fraction is elevated and why?
    Indirect due to excessive breakdown of RBCs by maternal antibody.
  46. What is the risk to the newborn from a high level of indirect bilirubin?
    Unconjugated bilirubin (indirect) has a high affinity for brain tissue and causes necrosis (kernicterus). Without appropriate treatment, mental retardation, hearing deficits, or cereral palsy may result.
  47. At what level of bilirubin would an exchange transfusion be indicated in a neonate?
    Each institution establishes its own criteria, but an exchange transfusion is usually performed when the unconjugated bilirubin reaches 20 mg/dl.
  48. What method is used to determine neonatal bilirubin?
    Direct spectrophotometry at 454 nm. This method can't be used for patients over one month of age because of interfering lipochromes, such as carotene. 
  49. Name two conditions in which direct bilirubin is elevated.
    Hepatic and posthepatic jaundice.
  50. What are the typical lab findings in post hepatic jaundice?
    Increased total bilirubin, increased direct bilirubin, decreased urine urobilinogen, and clay-colored stools.
  51. Which disorder results in the highest levels of conjugated bilirubin?
    Obstructive liver disease.
  52. What type of method is used for most hormone assays?
  53. What is the precursor in the biosynthesis of all steroid hormones?
  54. List several steroid hormones.
    Cortisol, aldosterone, estrogen, testosterone, progesterone.
  55. Which endocrine gland releases tropic hormones that regulate other endocrine glands?
    The anterior pituitary
  56. Where is follicle-stimulating hormone (FSH) produced and what is its main action?
    It is produced in the anterior pituitary. It stimulates production of sperm and eggs. There is a sharp increase in FSH just before ovulation. 
  57. Where is growth hormone (GH) produced and what is its main action?
    It is produced in the anterior pituitary. It stimulates protein synthesis and cell growth and division. 
  58. Where is thyroid-stimulating hormone (TSH) produced and what is its main action?
    It is produced in the anterior pituitary. It stimulates the thyroid to produce T3 and T4. It is also known as thyrotropin. 
  59. Where is adrenocorticotropic hormone (ACTH) produced and what is its main action?
    It is produced in the anterior pituitary. It stimulates the adrenal cortex to produce corticosteroids. ACTH exhibits diurnal variation. Levels are highest in early morning and lower in late afternoon. 
  60. Where is anti-diurectic hormone (ADH) produced and what is its main action?
    It is produced in the hypothalamus and stored in the posterior pituitary. It regulates reabsorption of water from the distal convoluted tubules. ADH is decreased in diabetes insidious, leading to the excretion of an increased volume of dilute urine. 
  61. Where is cortisol produced and what is its main action?
    It is produced in the adrenal cortex. It regulates carbohydrate, fat, and protein metabolism, water and electrolyte balance, and suppresses inflammatory and allergic reactions. Cortisol levels are regulated by ACTH and show diurnal variation. Levels in the evening are approximately 2/3 of morning levels. Cortisol is increased in Cushing's syndrome and decreased in Addison's disease. 
  62. What is Addison's disease?
    Adrenal insufficiency, characterized by decreased cortisol and increased ACTH.
  63. What is Cushing's syndrome?
    The signs and symptoms associated with elevated cortisol levels. Cushing's syndrome may be due to tumors of the pituitary (Cushing's disease), tumors of the adrenal glands, ectopic ACTH-secreting tumors, or administration of glucocorticoids or ACTH. 
  64. What do 17-ketosteroids and 17-hydroxycorticosteroids measure?
    Adrenal cortical function
  65. Interpret this patient's plasma cortisol results:
    8 AM: 30ug/dl (reference range 5-23ug/dl)
    4 PM: 32 ug/dl (reference range 3-16ug/dl)
    The patient has hypercortisolism and no diurnal variation. Hypercortisolism is referred to as Cushing's syndrome. One cause of Cushing's syndrome is Cushing's disease, the result of an ACTH-roducing pituitary adenoma. Other causes of Cushing's syndrome are tumors of the adrenal glands, ectopic ACTH-screening tumors, and administration of glucocorticoids or ACTH. 
  66. What is aldosterone produced and what is its main action?
    It is produced in the adrenal cortex. It increases retention of Na+ and excretion of Kand H
  67. What are catecholamines?
    The hormones secreted by the adrenal medulla--epinephrine, norepinephrine, and dopamine. Their metabolite is vanillylmandelic acid (VMA). 
  68. What is a pheochromocytoma?
    A tumor of the adrenal medulla that produces large amounts of catecholamines and causes hypertension. It can be diagnosed by urinary metanephrines, VMA, and plasma catecholamines. 
  69. What substances can cause a false positive VMA?
    Bananas, vanilla, and some drugs. Because of the interfering factors in the VMA test, urinary metanephrines is considered the best screening test for pheochromocytoma
  70. Where is progesterone produced and what is its main action?
    It is produced in the ovaries. It prepares the uterus for pregnancy and stimulates lactation. 
  71. What is the major estrogen produced by the ovaries?
    Estradiol (E2). Estrogens are involved in the development of the female reproductive organs and secondary sex characteristics, regulation of the menstrual cycle, and maintenance of pregnancy 
  72. Which hormones are used to assess fetal well-being?
    Estriol, progesterone and it metabolite, pregnanediol.
  73. Which hormone is used to detect pregnancy?
    Human chorionic gonadotropin (HCG). It is secreted by the placenta. HCG doubles approximately every 2 days during the first trimester, then slowly declines in the second and third trimester. HCG can also be used to detect and monitor cancers of the ovaries, testes, and placenta. The beta subunit is measured to increase the specificity of the test. The alpha subunits are identical to those of LH and FSH
  74. Which hormone can be measured by a home testing kit to determine the time of ovulation?
    Luteinizing hormone (LH), secreted by the anterior pituitary. There is a sharp peak just before ovulation.
  75. Why are estrogen and progesterone receptor assays performed?
    To establish a prognosis for patients with great cancer. 
  76. Where is thyroxine (T4) produced and what is its main action?
    It is produced in the thyroid and controls metabolic rate, growth and development, and sexual maturation. Triiodothyronine (T3) is formed primarily form deiodination of T4 by tissues. 
  77. Which is the physiologically active form of T4?
    Free T4 (FT4). Most T4 is bound to thyroxine binding globulin (TBG), the main carrier protein for T4 and T3. 
  78. What is the recommended screening test for thyroid function?
    Recent improvements in sensitivity have made TSH the most important indicator of primary hyperthyroidism and hypothyroidism. With hypothyroidsm, TSH may be increased before clinical symptoms. A normal TSH usually excludes a diagnosis of primary thyroid dysfunction. 
  79. What further thyroid testing is recommended when the TSH is abnormal?
    Free T4
  80. What further thyroid testing is recommended when the TSH is low and the free T4 is low or normal?
    A total T3 to test for T3 thyrotoxicosis. T3 thyrotoxicosis is hyperthyroidism with elevated T3 and normal T4 and free T4. 
  81. How can primary hypothyroidism be different from secondary hypothyroidism?
    By TSH. Primary hypothyroidism is disorder of the thyroid gland. TSH increases as the pituitary tries to stimulate the thyroid to produce more T3 and T4. Secondary hypothyroidism is a pituitary disorder. TSH levels are low. 
  82. Discuss the use of the total T4 and T3 uptake.
    When free T4 testing was beyond the capabilities of most clinical labs, total T4 and T3 uptake were performed in order to calculate the free thyroxine index (FT4I) or T7, an estimate of free T4. Today, free T4 assays are readily available and provide a more accurate picture of the patient's thyroid status than status than total T4 and total T3, which are affected by abnormal concentrations of binding proteins, such as TBG. 
  83. What lab findings are typical of primary hypothyroidism?
    High TSH and low T4. T3 levels are not routinely performed. Although T3 is decreased in patients who are severely hypothyroid, it is with in the reference range in 15-30% of hypothyroid patients.
  84. What screening is done for neonatal hypothyroidism?
    All 50 states require newborn screening for hypothyroidism to eliminate severe mental retardation associated with thyroid hormone deficiency. Measurement of T4 or TSH or a combination of test is performed using dry blood spots or cord blood. 
  85. What lab findings are typical of hyperthyroidism?
    TSH is low and free T4 in high. In over 90% of patients with hyperthyroidism, both serum T3 and T4 levels are increased, with the increase in T3 greater than the increase in T4; however, only free T4 is routinely measured. 
  86. What is Grave's Disease?
    An autoimmune disease that is the most common type of hyperthyroidism in the U.S. Thyroid stimulating hormone receptor antibodies (TRab) are present in the serum. 
  87. Where is parathyroid hormone (PTH) produced and what is its main action?
    It is produced in the parathyroid glands. It increases serum calcium and decreases phosphates. PTH is increased in primary hyperparathyroidism and decreased in hypoparathyroidism. 
  88. What is actually measured when serotonin is ordered?
    5-HIAA, the urinary metabolite of serotonin. Increased levels occur with argentaffinoma, a tumor of the GI tract. Bananas,walnuts, pineapples, plums, eggplants, and avocados cause false positive 5-HIAA
  89. Where is glucagon produced and what is its main action?
    It is produced in the alpha cells of the pancreas. It increases glucose levels.
  90. What are electrolytes?
    Substances that carry an electric current when dissolved in water. Anions are negatively charged and cations are positively charged. 
  91. What are the major electrolytes?
    Sodium, potassium, chloride, and bicarbonate.
  92. What is the Law of Electric Neutrality?
    The number of cations in the body must equal the number of anions. If a cation increases, either another cation must decrease or an anion must increase to maintain electric neutrality.