Lab. 12 & 13 Renal Function Tests PDF

1 Lab. 12 & 13 Renal function tests Kidney structure Anatomy The kidneys are bean-shaped organs. In humans, the kidneys are located in the posterior part of the abdominal cavity. There are two, one on each side; the right kidney sits just below the diaph ragm and posterior to the liver, the left be...

1 Lab. 12 & 13 Renal function tests Kidney structure Anatomy The kidneys are bean-shaped organs. In humans, the kidneys are located in the posterior part of the abdominal cavity. There are two, one on each side; the right kidney sits just below the diaph ragm and posterior to the liver, the left below the diaphragm and posterior to the spleen. Above each kidneythere is an adrenal gland (also called the suprarenal gland). The asymmetry within the abdominal cavitycaused by the liver results in the right kidney being slightly lower than the left one. Kidney function Excretory function  The kidneys produce and excrete urine, which rids the body of the end products of metabolism  Elimination of certain foreign toxic substances and drugs before or after they are metabolizedin the liver. Regulatory function The primary role of the kidneys is to maintain the homeostatic balance of bodily fluids by filtering and secreting metabolites and minerals from the blood.  Electrolyte homeostasis Kidneys acts to regulate plasma volume by regulating water and electrolyte balance so any significant rise or drop in plasma osmolality is detected by the hypothalamus, which causes the pituitary gland to secrete antidiuretic hormone, resulting in water reabsorption by the kidney andan increase in urine concentration.  Blood pressure regulation Kidney plays a role in blood pressure regulation by regulation of Sodium ions through the secretion of renin hormone which acts on angiotensinogen to produce angiotensin-I which converted in the lung to angiotensin-II that stimulate aldosterone secretion (increasing sodium reabsorption) and constrict blood vessels, this rise blood pressure by increasing the blood volume and increasing the vascular peripheral resistance. Endocrine function The kidneys synthesize hormones such as:  Erythropoietin Erythropoietin is a glycoprotein hormone produced by specialized cells in the kidneys and it regulates the production of red blood cells (RBCs) in the marrow.  2  Renin Renin is produced within juxtaglomerular cells after processing and cleavage of protein, which is produced in the liver. The primary stimuli for renin release are the reduction of renal perfusion pressure and hyponatremia.  Active vitamin D  Vitamin D can either be ingested with food or made from 7- dehdrocholesterol by the action of ultraviolet light. The liver converts cholecalciferol ( vitamin D) into 25-hydroxycholecalciferol and the proximal tubule cells of the kidney convert 25-hydroxycholecalciferol into 1, 25- dihydroxycholecalciferol. This is the active form of vitamin D. Renal function tests Why renal function tests are required?  Determine whether the kidneys are functioning normally.  Monitor the progress of kidney disease.  Monitor the kidney function of people who take medications that can cause kidney damage.  Monitor the effectiveness of dialysis and other treatments related to failure  Ordered in cases of high blood pressure to assess kidney function Blood urea  Overview Ammonia is produced in the liver when protein is broken into its component parts (amino acids) and metabolized. The nitrogen combines with other molecules in the liver to form the waste product urea. The urea is then released into the bloodstream and carried to the kidneys, where it is filtered out of the blood and excreted in the urine. Since this is an ongoing process, there is usually a small but stable amount of urea in the blood. The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions occurring in many animals that produces urea (NH2 )2CO from ammonia (NH3 ).  Sample Serum or plasma Note: Do not eat a lot of meat or other protein in the 24 hours before having a blood urea nitrogen (BUN) test (fasting is recommended).  Normal: 15 – 45 mg/dl Note:  3 BUN levels in very young babies are about 2/3 of the levels found in healthy young adults, while levels in adults over 60 years of age are slightly higher than youngeradults.  Interpretation: Azotemia is another word that refers to high levels of urea, but is used primarily when the abnormality is not yet so severe as to produce symptoms. Uremia is a term used to describe the illness accompanying kidney failure (also called renal failure) Serum creatinine  Overview Creatine is synthesized in the liver, pancreas, and kidneys from the amino acids arginine,glycine, and methionine. Creatine is transported through the circulatory system to muscle where it is converted to phosphocreatine and acts as an energy reservoir much like ATP. Creatinine is a waste product produced in your muscles from the breakdown of creatine (Creatinine is formed by the hydrolysis of creatine). Almost all creatinine is excreted by the kidneys, so blood levels are a good measure of how well your kidneys are working. Why it is done? Determine whether the kidneys are functioning normally. Serum creatinine is a more specific and sensitive indicator of renal disease than BUN why? Production of creatinine depends on an individual's muscle mass, which usually fluctuates very little. With normal kidney function, then, the amount of creatinine in the blood remains relatively constant and normal. For this reason, and because creatinine is affected very little by liver function, an elevated blood creatinine is a more sensitive indication of impaired kidney function than the BUN Disadvantage of creatinine Unfortunately, serum creatinine is very insensitive to even substantial declines in glomerular filtration rate. Glomerular filtration rate may be reduced by up to 50% before serum creatinine becomes elevated.  Sample Serum or plasma Stability in serum: Creatinine in serum is stable for twenty-four (24) hours at refrigerated temperatures (2 - 8°C) and several months when frozen (-20° C).  4  Normal: Male: 0.7–1.3 mg/dl female: 0.6–1.1 mg/dl Note: The quantity produced depends on the size of the person and their muscle mass. For this reason, creatinine concentrations will be slightly higher in men than in women and children.  Interpretation: Causes of high creatinine Prerenal causes  Caused by a decrease in cardiac output, resulting in inadequate blood supply to the kidneys as in heart disease, dehydration, excessive blood loss that causes shock  Caused by Muscle disease such as acromegaly or myasthenia gravis Renal causes  Impaired kidney function; 50% loss of renal function is needed to increase serum creatinine from 1.0 to 2.0 mg/dL; therefore the test is not sensitive for mild to moderate renal injury  Creatinine levels increase more slowly than blood urea nitrogen (BUN) levels, so an increase in creatinine usually indicates chronic kidney problems. Postrenal causes  As in postrenal azotemia Causes of low creatinine Low levels of creatinine are not common and are not usually a cause for concern. Low blood creatinine levels can indicate:  A diet very low in protein.  A decrease in muscle mass caused by a disease, such as muscular dystrophy.  Pregnancy can also cause low blood creatinine levels. Creatinine Clearance  The measurement of accurate renal function is vital for the routine care of patients. Determining the renal function status can predict kidney disease progression and prevent toxic drug levels in the body.  The glomerular filtration rate (GFR) describes the flow rate of filtered fluid through the kidneys. The gold standard measurement of GFR involves the injection of inulin and its clearance by the kidneys.  5  However, the use of inulin is invasive, time-consuming, and an expensive procedure. Alternatively, the biochemical marker creatinine found in serum and urine is commonly used in the estimation of GFR.  Creatinine clearance (CrCl) is the volume of blood plasma cleared of creatinine per unit time. It is a rapid and cost-effective method for the measurement of renal function. Both CrCl and GFR can be measured using the comparative values of creatinine in blood and urine.