Capstone 51-70 Chemistry

BUN (Blood Urea Nitrogen), creatinine, and uric acid

The end product of protein metabolism. It is synthesized in the liver from ammonia and carbon dioxide.

10-20 mg/dl

Refers to elevated levels of urea in the blood

Fluoride and citrate inhibit urease.

Urea=BUN x 2.14

In muscles

The anhydride of creatine. Creatinine is formed from creatine by splitting out of water

The Jaffe reaction using alkaline picrate. It is a nonspecific, but still clinically useful, method.

0.5-1.5 mg/dl

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.

45/2.1=21.4

The normal ratio is 12-20. A ratio greater than 20 is suggestive of preener azotemia.

Creatinine, because it is related to muscle mass and is not affected by diet.

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.

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.

Uricase. The preservative sodium fluoride must not be used to collect the blood sample because it destroys uricase. 

3.0-7.0 mg/dl

Urate crystals may preciptate in joints and tissue. 

To prevent precipitation of uric acid. Uric acid precipitates at acid pH.

Mainly in the intestines from deamination of amino acids. It is converted to urea by the liver. 

20-60 ug/dl

With hepatic failure and Reye's syndrome. High levels are neurotoxic

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.

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. 

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. 

False negatives.

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.

The degradation product of heme. It is produced in the reticuloendothelial cells following breakdown of RBCs. 

Albumin

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.

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. 

It is a sign of obstruction of the bile duct. Urobilin is not being produced because bilirubin is not reaching the intestines. 

Only urobilinogen. Bilirubin should not be present in urine.

Decreased urobilinogen.

Total and direct. The indirect level is calculated by subtracting direct from total.

Direct bilirubin is soluble in water; indirect bilirubin is not. Both are soluble in alcohol.

Only direct bilirubin.

Diazotization with sulfanilic acid. Bilirubin reacts with diazotized sulfanilic acid to produce azobilirubin.

Alcohol or caffeine-benzoate-acetate can be used to make the indirect bilirubin soluble.

Exposure to light. Hemolysis will also cause a decreased level by the Jendrassik-Grof method.

0.2-1.0 mg/dl. Conjugated (direct) bilirubin is <0.2 mg/dl.

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

Prehepatic jaundice, for example, hemolytic transfusion reaction, hemolytic anemia, or hemolytic disease 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.

Indirect due to excessive breakdown of RBCs by maternal antibody.

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.

Each institution establishes its own criteria, but an exchange transfusion is usually performed when the unconjugated bilirubin reaches 20 mg/dl.

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. 

Hepatic and posthepatic jaundice.

Increased total bilirubin, increased direct bilirubin, decreased urine urobilinogen, and clay-colored stools.

Obstructive liver disease.

Immunoassays

Cholesterol

Cortisol, aldosterone, estrogen, testosterone, progesterone.

The anterior pituitary

It is produced in the anterior pituitary. It stimulates production of sperm and eggs. There is a sharp increase in FSH just before ovulation. 

It is produced in the anterior pituitary. It stimulates protein synthesis and cell growth and division. 

It is produced in the anterior pituitary. It stimulates the thyroid to produce T3 and T4. It is also known as thyrotropin. 

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. 

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. 

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. 

Adrenal insufficiency, characterized by decreased cortisol and increased ACTH.

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. 

Adrenal cortical function

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. 

It is produced in the adrenal cortex. It increases retention of Na⁺ and excretion of K⁺ and H⁺ 

The hormones secreted by the adrenal medulla--epinephrine, norepinephrine, and dopamine. Their metabolite is vanillylmandelic acid (VMA). 

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. 

Bananas, vanilla, and some drugs. Because of the interfering factors in the VMA test, urinary metanephrines is considered the best screening test for pheochromocytoma

It is produced in the ovaries. It prepares the uterus for pregnancy and stimulates lactation. 

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 

Estriol, progesterone and it metabolite, pregnanediol.

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

Luteinizing hormone (LH), secreted by the anterior pituitary. There is a sharp peak just before ovulation.

To establish a prognosis for patients with great cancer. 

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. 

Free T4 (FT4). Most T4 is bound to thyroxine binding globulin (TBG), the main carrier protein for T4 and T3. 

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. 

Free T4

A total T3 to test for T3 thyrotoxicosis. T3 thyrotoxicosis is hyperthyroidism with elevated T3 and normal T4 and free T4. 

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. 

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. 

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.

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. 

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. 

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. 

It is produced in the parathyroid glands. It increases serum calcium and decreases phosphates. PTH is increased in primary hyperparathyroidism and decreased in hypoparathyroidism. 

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

It is produced in the alpha cells of the pancreas. It increases glucose levels.

Substances that carry an electric current when dissolved in water. Anions are negatively charged and cations are positively charged. 

Sodium, potassium, chloride, and bicarbonate.

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.