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27 Cards in this Set
- Front
- Back
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Urea
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-made by liver as a means of disposing of ammonia
-excreted in urine- filter through glomerulus and reabsorpbed in proximal tubule -BUN (bl urea nitrogen) = measurement of the nitrogen portion of urea -serum elevation indicator of renal disease |
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BUN
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-blood sample: 5 mL serum
-RR: adult- 5-20 mg/gL; elderly 8-23 -uremia = toxic amt of BUN -azotemia = increased level of all nitrogenous compounds |
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Causes of uremia
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1. inc protein metabolism: excesive dietary protein, stress, GI bleeding
2. impaired kidney function: pre-renal uremia (prob before blo flow gets to kidney) (60-70%), renal uremia, post-renal uremia |
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pre-renal uremia
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-mechanism occurs prior to filtration of blood by glomerulus
1. decreased blood flow to kidneys: SHOCK, DEHYDRATION, CHF, HEMORRHAGE 2. glomerular P and perfusion changes to medications: NSAIDS, ACE inhibitors -urine sediment relatively normal |
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Renal uremia
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-secondary to disease or toxicity of glomerulus, renal microvasculature or renal tubules
1. glomerulonephritis 2. pyelonephritis 3. acute tubular necrosis 4. chronic interstitial nephritis 5. nephrotoxic meds -abnl urine sediment |
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post renal uremia
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-Occurs secondary to obstruction of 1. lower urinary tract
2. Enlarged prostate 3. Hydronephrotic kidneys 4.Ureteral obstruction 5. Renal calculi 6. Tumors -urine sediment relatively nml unless concurrent infection |
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low levels of BUN other reasons
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-inc plasma vol: 1. late preg, 2. overhydration
3. severe liver disease 4. lack of protein |
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Creatinine
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-End product in metabolism of creatine
-Proportional to muscle mass -Removed from circulation by kidneys |
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creatinine etc.
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-Produced and excreted relatively unaltered at fairly constant rate by glomerular filtration
--Minimally affected by diet and blood flow --Good estimate of glomerular filtration function -More sensitive and specific than BUN for testing renal function -May take 50-60% renal function impairment to see change in creatinine |
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creatinine reference ranges
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Adult male: .6-1.3 mg/dlL
adult female: .5-1 child: .5-1 |
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why would you see an elevated serum creatinine
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1. Renal disease
2. Meat rich diet 3. Very large muscle mass 4. Muscle disorders 5. Aging 6. Medications (ascorbic acid, cephalosporins, trimethoprim-sulfamethoxazole (Bactrim), nephrotoxic chemotherapy agents) |
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decreased serum creatinine
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1. Short stature
2. Small muscle mass 3. Liver disease 4. Inadequate protein diet 5. Elevated serum bilirubin or glucose |
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creatinine clearance
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-Reflects ability of kidneys to clear the plasma of a substance (creatinine)
-Reflects overall level of glomerular functioning |
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CC=
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U creat (mg/dL) x U vol (mL)/ #min/ (plasma creat) x (1.73/BSA)
RR: male: 14-26 mg/kg/day female: 11- 20 mg/kg/day |
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CC specimesn 24 hours urine sample
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1. Discard first urine and note time
2. Collect all remaining urine for 24 hours 3.Include last voided specimen 4.Refrigerate specimen 5.Avoid vigorous exercise, coffee, tea, meats 6. Encourage fluid intake 7.Label with time frame and patient name -plasma creatinine specimen: midpoint of time frame is best |
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bedside estimation of CC
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(140 - age in yrs) (wt in kg) / (72 x (serum creatinine))
(multiple result by .85 for women with lean body mass) -Should only use for patients 20-80 years old with stable renal function and no edema or obesity |
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decreased creatinine clearance
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1. Nephrotoxicity 2. Aging
3. Renal insufficiency/failure Shock Hypovolemia Congestive heart failure Acute glomerulonephritis Acute tubular necrosis Pyelonephritis 4. unreliable in proteinuria and advanced renal failure |
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other reasons for a decreased and increased creatinine clearance
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1. decreased: incomplete urine specimen, bacterial contamination
2. increased: exercise, pregnancy |
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Summary of indications for ordering a BUN and creatinine
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1. Estimate kidney function
2. Monitor severity of kidney disease 3. Monitor treatment of kidney disease 4. Determine if severe dehydration is present 5. Newly diagnosed high blood pressure or diabetes 6. Follow up abnormal urinalysis 7. Any medical problem serious enough to admit patient to hospital |
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Other tests of renal function
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BUN: creatinine ratio
1. Helps distinguish causes of azotemia 2. Reference value ~10:1 3. Values over 10:1 and especially over 20:1 are associated with PRE-RENAL causes of azotemia |
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Fractional excretion of sodium (FEna)
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-estimates ability of renal tubules to concentrate or dilute glomerular filtrate
FEna = (urine NA) x (serum creatinine) / [(serum Na) x (urine creatinine)] values < 1% indicate prerenal azotemia > 1-2% indicate acute tubular injury |
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fractional excretion of sodium: factors to consider
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-pts taking diuretics may have prerenal azotemia but FEna may be increased by diuretic induced Na excretion
- chronic renal insufficiency pts with prerenal azotemia are unable to reabsorb enough Na and FEna may be >1% |
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Uric acid
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-end product of purine metabolism
-produced in liver and primarily filtered through kidneys (70%) -daily serum levels highly variable -test specimen - 5mL serum or plasma |
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uric acid test indications
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1. suspected renal failure
2. follow up pts on chemo or radiation therapy 3. suspected gout or uric acid nephropathy |
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uric acid reference ranges
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adult male: 4.0- 8.5 mg/dL
adult female: 2.7 - 7.3 mg/ dL children: 2.0 - 5.5 mg/dL |
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elevated uric acid (hyperuricemia)
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1. renal failure
2. increased breakdown of nucleoproteins (chemotherapeutic agents, leukemia, lymphoma etc) 3. uric acid crystal and stones deposition (gout and renal stones) 4. stress, exercise 5. purine rich diets 6. thiazide diuretics and low dose aspirin |
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decreased uric acid result
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1. severe liver disease
2. low purine diet 3. allopurinol, probenacid, steroids, large doses of aspirin |
