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Final Exam
Renal Function Tests
47
Science
Graduate
04/11/2013

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Term
basic urinalysis
Definition
The most common test for assessing renal function
Term
Basic Urinalysis assesses (5)
Definition
pH – Acidity/Alkalinity
Specific gravity (concentrating ability)
Protein Concentration – Initial indicator of disease
Nitrite Concentration – Bacterial Infection
Blood
Term
6 things to evaluate when a significant disease is suspected
Definition
Renal Blood flow
Glomerular filtration rates
Clearance capabilities
Tubular reabsorption capabilities
Tubular secretion capabilities
Term
Glomerular Filtration Tests
Definition
The standard test for measuring filtering capacity of the kidney is the clearance test.
Term
Clearance tests measure the rate of what?
Definition
rate at which the kidneys are capable of removing a filterable substance from the blood
Term
Important factors in clearance tests (5)
Definition
Substance must neither be reabsorbed or secreted by the kidney tubules
Substance must be stable during the collection period ( usually 24 hrs)
Consistency of the plasma level
Substance’s availability to the body
Test availability
Term
The clearance of a substance (definition)
Definition
volume of plasma from which that substance is completely cleared by the kidney per unit of time
Term
Does every substance in the blood have a unique clearance rate?
Definition
Yes
Term
Units of clearance rate?
Definition
volume/plasma / time
Term
Why is Inulin used for clearance tests?
Definition
Not a normal body substance requires constant infusion throughout the test period (exogenous procedure)
Term
Inulin
Definition
Polymer of fructose that is extremely stable and not reabsorbed or secreted by the tubules
Term
Why is inulin clearance test not used often
Definition
suitable endogenous procedure is available
Term
Creatinine Clearance Test.
Definition
This test evaluates how efficiently the kidneys clear a substance called creatinine from the blood.
Term
Creatinine
Definition
a waste product of muscle energy metabolism, is produced at a constant rate that is proportional to the muscle mass of the individual
Term
Why is craetinine clearance specific for kidney function?
Definition
Because the body does not recycle it, all of the creatinine filtered by the kidneys in a given amount of time is excreted in the urine
Term
Why kind of urine sample is the creatinine clearance test performed on?
Definition
timed urine specimen--a cumulative sample collected over a two to twenty-four hour period. Determination of the blood creatinine level is also required to calculate the urine clearance.
Term
Disadvantages to Creatinine test (5)
Definition
Some creatinine is secreted by the tubules and secretion increases as blood levels rise
Chromogens in blood plasma react with the chemical analysis
Creatinine breakdown by bacteria if specimens are kept at room temperature
Heavy meat diet during collection period may influence results if plasma levles are drawn prior to the urine collection period
Inaccurate in patients with muscle wasting diseases
Term
Urea
Definition
waste product that is created by protein metabolism and excreted in the urine.
Term
requirements of the urea clearance test?
Definition
The urea clearance test requires a blood sample to measure the amount of urea in the bloodstream and two urine specimens, collected one hour apart, to determine the amount of urea that is filtered, or cleared, by the kidneys into the urine.
Term
Clearance Tests Calculations, Standard formula
Definition
C= UV/PT

C = ml. plasma cleared per minute
U = urine concentration
P= Plasma concentration
V= Volume
T = collection period (mins)
Term
Normal GFR
Definition
120-125mls/min
Term
Corrected Clearance formula
Definition
C = UV/PT X 1.73 Square Meters/Patient Surface Area
Term
GFR is dependent on
Definition
functional capacity of the nephrons not by the number of functioning nephrons
Term
Is creatinine clearance a good detection for early renal disease?
Definition
no
Term
uses of the creatinine clearance test? (3)
Definition
Determine extent of nephron damage in known renal disease
Monitor effectiveness of treatment in preventing further nephron damage
Feasibility of administering medications that may be toxic in cases of reduced GFR
Term
First functional change in renal disease
Definition
Loss of tubular reabsorption capabilities
Term
concentration tests
Definition
address the reabsorption of salts and water
Term
urine concentration is largely determined by
Definition
body’s hydrational status.
Term
Patients with normal concentrating abilities should have a specific gravity of _____ when deprived of fluids for 16 hours
Definition
1.025
Term
Osmolality
Definition
– depends on the number of particles present in solution
Term
beta2 microglobulin
Definition
Good correlation between the GFR and the plasma levels of beta2 microglobulin has been demonstrated.
Term
What is Beta2 microglobulin
Definition
Molecule dissociates from the human leukocyte antigens at a constant rate and is rapidly cleared from the plasma.
Term
Increased levels of beta2 microglobulin has been shown to be a more sensitive indicator of
Definition
decreased GFR than the creatinine clearance
Term
When is the beta2 microglobulin not reliable?
Definition
Test is not reliable in patients with malignancy or immunological disorders
Term
Clinical Significance of Tubular Reabsorption Tests
Definition
Evaluates renal concentrating abilities
Monitoring the course of renal disease
Monitoring fluid and electrolyte therapies
Differential diagnosis of hypernatremia and hyponatremia and polyuria
Evaluating secretion of and renal response to ADH
Term
Tubular Secretion and Renal Blood Flow
Definition
Tests to measure tubular secretion of nonfiltered substances and renal blood flow are closely related in as much as total renal blood flow through the nephron must be measured by a substance that is secreted rather than filtered through the glomerulus.
Term
Abnomalities in Tubular Secretion and Renal Blood Flow tests
Definition
related to either impaired secretion or inadequate presentation of the substance to the capillaries
Term
most common Tubular Secretion and Renal Blood Flow tests
Definition
PAH – para aminohippuric acid test
PSP – phenolsulfonphthalein test
Term
Para Amino Hippurate Test principle
Definition
Principles are the same as the clearance test however the substance must be removed from the plasma in the peritubular capillaries rather than at the glomerulus
Term
Why does PAH fulfill the criteria for a clearance test?
Definition
It is a high MW substance that binds loosely to plasma proteins and is completely removed in the peritubular capillaries.
Term
How to ensure accurate PAH results?
Definition
The quantity of PAH infused must be monitored
Term
PAH clearance is a method used to measure
Definition
renal plasma flow, which, in turn, is a measure of renal function.
Term
Renal Perfusion flow calculation
Definition
RPF = U(pah)/P(pah) x v

P(pah)= PAH in aterial blood
U(pah) = PAH in urine
V = urine flow
Term
eRPF almost equals RPF because
Definition
the renal extraction ratio of PAH almost equals 1
Term
The renal extraction ratio of PAH in a normal individual is
Definition
0.92
Term
What do you need to take into account when measures RPF with PAH?
Definition
, this method usually underestimates RPF by approximately 10%.
Term
Why is it okay for the PAH test to be inaccurate?
Definition
considering the ease with which eRPF is measured
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