Quiz 1: Renal Function Flashcards Preview

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Flashcards in Quiz 1: Renal Function Deck (25)
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Renal Function in Acid/Base Balance

Bicarbonate ions & H+ ions are produced within the tubules as a result of carbonic anhydrase
• H2O + CO2 to H2CO3 to H+ + HCO3-


Glomerular filtrate

Glomerular filtrate is a plasma filtrate where glucose and protein are reabsorbed
• filtration influenced by: cellular structure, hydrostatic pressure, under feedback of Aldosterone/Renin system, number of functioning nephrons



Skeletal muscle dehydration product which is excreted into circulation at a relatively constant rate proportional to the amount of muscle mass and regulated by kidney function
Increased serum Creatinine indicates Renal Disease/Failure


Uric Acid

From breakdown of purines, most is reabsorbed in proximal tubule
Increased in Gout, Renal Failure, Leukemia, and Chemotherapy



Blood Urea Nitrogen
• Greatly affected by renal function and perfusion
• Abnormal levels due to decreased renal blood flow from: CHF, shock, dehydration, hemorrhage
• “Azotemia”: high BUN
• “Uremia”: azotemia with renal failure


Clearance Tests

• Measures the rate at which the kidneys remove a substance within a timed interval
• Endogenous vs. Exogenous
Endogenous examples: urea, creatinine, originating or produced within the individual
Exogenous examples: inulin, radioisotopes, para amino hippurate (PAH) test


Exogenous Clearance Tests

Originating or produced outside, drugs administered to patients, & methods may cause adverse reactions.
•Insulin: introduced into patient via IV/oral then voided for measurement
• Radioisotopes: Show nuc med renogram
• PAH: para amino hippurate: injected via IV, cleared rapidly by kidneys within half hour. Measured in urine, measurement of renal secretion


Creatinine Clearance Test

• Clearance = (U x V) / P : urinary creatinine x total volume divided by Plasma creatinine
Corrected Cr Cl = Cr Cl X 1.73 / BSA
• greatest source of error is in the collection of the ENTIRE specimen
• Correction for ht/wt by using nomograms
• Avoid measurements in early renal and muscle- wasting diseases


Clinical Implications of Uric Acid Testing

• Hyperuricemia: Gout, Chemotherapy, Menopause, Renal disease, Lesch-Nyhan syndrome: genetic deficiency of enzyme needed for synthesis of purines
• Hypouricemia: less common, Over treatment of cancer therapy due to liver damage


Renal Tubular Reabsorption Tests

• Assessment of renal concentration and dilution ability of renal tubules
Tested by:
1) specific gravity
• refractometer
• urinometer
2) osmolality
• freezing point depression (Value increases in proportion to the increase of solutes regardless of the type- equally influenced by large and small molecules, refers to the number of moles of solute / per kilogram of solvent, one mole of solute / one liter solvent = one osmole)
• vapor depression (volatile solutes can interfere)



Can be detected if specific gravity is measured throughout the day
Hallmark of renal failure - Kidneys lack the ability to concentrate or dilute urine so that the blood filtrate remains unchanged and respond to the body’s hydration status


Glomerular Filtration Rate (GFR)

Best overall index of kidney function in health and disease.
Normal GFR varies according to age, sex, and body size; in young adults it is approximately 120-130ml/min/1.73 m2 and declines with age.


List Renal Tests

3.Uric Acid
4.Creatinine Clearance


Non-Protein Nitrogens

Urea, Creatinine, Uric Acid, Ammonia



Urea, Creatinine, Uric Acid, Ammonia increased in the plasma during renal impairment


Creatinine Clearance Equation

[Urine Creatinine/Serum Creatinine] x [Vl 24hr urine/Time elapsed (usually 24hr)]
Expressed in mL/min
Correction for Body Surface Area: Clearance x [1.73/area]


Jaffe Reaction

Classic Method of Creatinine Clearance Measurement
Creatinine reacts with picric acid in alkaline sln that is measured spectrophotometrically
Interferents include Glucose, Aceotoacetate, and Ascorbic Acid


BUN Measurement

Kinetic Method: Urease hydrolyzes urea into ammonia that can be measured with ISE or spectrophotometrically
Chemical Method: Diacetyl and Urea combine to give a diazine derivative that is yellow in color


BUN/Creatinine Ratio

Normally about 10:1 and 20:1


Uric Acid measurement

Uric Acid reduces phosphotungstic acid to tungsten blue measured spectrophotometrically



Product of deamination of Amino Acids normally metabolized by Liver into Urea
High levels are toxic to CNS, found in Advanced Liver Disease (Reye's Syndrome, Cirrhosis, Viral Hepatitis) and Impaired Renal function


Causes of Falsely Elevate Ammonia Levels

Failure to test in timely manner or place on ice during transport, poor venipuncture, incomplete collection tube filling



Major Nitrogen containing compound in blood from protein catabolism in the Liver then excreted by Kidneys
Abnormal levels may be due to prerenal, renal, or postrenal disorders
Increased: Renal failure, glomerular nephritis, urinary tract obstruction, congestive heart failure, dehydration, increased protein catabolism
Decreased: Severe Liver disease, vomiting/diarrhea


Converting BUN to Urea

BUN x 2.14 = Urea


Ammonia Measurement

Alpha-ketoglutarate, ammonia, and glutamate dehydrogenase react to form Glutamate and NADP+