TESTS TO MEASURE KIDNEY
FUNCTION, DAMAGE AND DETECT
ABNORMALITIES
Dr. Parin Hedayati
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An Introduction to the Urinary System
Produces urine
Transports urine
towards bladder
Temporarily store
urine
Conducts urine
to exterior
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• Healthy kidneys remove wastes and excess fluid
from the blood.
• Blood and urine tests show how well the kidneys are
doing their job.
• Urine tests can show how quickly body wastes are
being removed and whether the kidneys are leaking
abnormal amounts of protein.
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The Function of Urinary System
A) Excretion & Elimination:
removal of organic wastes products
from body fluids (urea, creatinine,
uric acid)
B) Homeostatic regulation:
Water -Salt Balance
Acid - base Balance
C) Enocrine function:
Hormones
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Kidney – basic data
• Urine excreted daily in adults:about 1.5L
• Kidneys only recieve 1% of total body weight
• The renal blood flow= 20% of cardiac output
• Plasma renal flow= PRF about 600 mL/Min./1.73
M2
• Reflects two processes
• Ultrafiltration (GFR): 180 L/day
• Reabsorption: >99% of the amount filtered
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Kidney Function
•A plumbers view
Input
Arterial
Filter
Processor
Output
Venous
Output
Urine
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How do you know it’s broken?
• Decreased urine
production
Input
Arterial
• Clinical symptoms
Filter
• Tests
Processor
Output
Venous
Output
Urine
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Where can it break?
Pre-renal
Input
Arterial
Renal
(intrarenal)
Filter
Processor
Output
Venous
Output
Urine
Post-renal
(obstruction)
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Causes of kidney functional disorders
• Pre-renal e.g. decreased
intravascular volum
• Renal e.g. acute tubular
necrosis
• Postrenal e.g. ureteral
obstruction
Why Test Renal Function?
• To identify renal dysfunction.
• To diagnose renal disease.
• To monitor disease progress.
• To monitor response to treatment.
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When should you assess renal function?
 Older age
 Family history of CKD
 Decreased renal mass
 Low birth weight
 Diabetes Mellitus (DM)
 Hypertension (HTN)
 Autoimmune disease
 Systemic infections
 Urinary tract infections (UTI)
 Nephrolithiasis
 Obstruction to the lower urinary tract
 Drug toxicity
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Biochemical Tests of Renal Function
 Measurement of GFR
 Clearance tests
 Plasma creatinine
 Renal tubular function tests




Osmolality measurements
Specific proteinurea
Glycouria
Aminoaciduria
 Urinalysis
 Appearance
 Specific gravity and osmolality
 pH
 osmolality
 Glucose
 Protein
 Urinary sediments
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Biochemical Tests of Renal Function
Measurement of GFR
Clearance tests
Plasma creatinine
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Measurement of glomerular filtration rate
 GFR can be estimated by measuring the urinary excretion of a
substance that is completely filtered from the blood by the
glomeruli and it is not secreted, reabsorbed or metabolized by the
renal tubules.
(Uinulin  V)
GFR =
Pinulin
 Clearance is defined as the (hypothetical) quantity of blood or
plasma completely cleared of a substance per unit of time.
 Inulin
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Biochemical Tests of Renal Function
Measurement of GFR
Clearance tests
Plasma creatinine
Urea, uric acid and β2-microglobulin
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• The normal value for GFR is 90 or above.
• A GFR below 60 is a sign that the kidneys are not working
properly.
• A GFR below 15 indicates that a treatment for kidney failure,
such as dialysis or a kidney transplant, will be needed.
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Creatinine
 1 to 2% of muscle creatine spontaneously converts to
creatinine daily and released into body fluids at a constant
rate.
 Endogenous creatinine produced is proportional to muscle
mass, it is a function of total muscle mass the production
varies with age and sex
 Dietary fluctuations of creatinine intake cause only minor
variation in daily creatinine excretion of the same person.
 Creatinine released into body fluids at a constant rate and its
plasma levels maintained within narrow limits  Creatinine
clearance may be measured as an indicator of GFR.
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Creatinine clearance and clinical utility
 The most frequently used clearance test is based on the
measurement of creatinine.
 Small quantity of creatinine is reabsorbed by the tubules and
other quantities are actively secreted by the renal tubules  So
creatinine clearance is approximately 7% greater than inulin
clearance.
 The difference is not significant when GFR is normal but when
the GFR is low (less 10 ml/min), tubular secretion makes the
major contribution to creatinine excretion and the creatinine
clearance significantly overestimates the GFR.
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Creatinine clearance clinical utility
An estimate of the GFR can be calculated from the creatinine content
of a 24-hour urine collection, and the plasma concentration within this
period.
Creatinine clearance in adults is normally about of 120 ml/min,
The accurate measurement of creatinine clearance is difficult, especially in
outpatients, since it is necessary to obtain a complete and accurately timed
sample of urine
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Use of Formulae to Predict Clearance
• Formulae have been derived to predict Creatinine
Clearance from Plasma creatinine.
• Plasma creatinine derived from muscle mass which is
related to body mass, age, sex.
• Cockcroft & Gault Formula
CC =K [(140-Age) x weight(Kg))] / serum Creatinine (mg/dL)
k = 1 for males & 0.85 for females
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Plasma Urea
Urea is the major nitrogen-containing metabolic product of protein
catabolism in humans,
 Its elimination in the urine represents the major route for
nitrogen excretion.
 More than 90% of urea is excreted through the kidneys, with
losses through the GIT and skin
 Urea is filtered freely by the glomeruli
 Urea production is increased by a high protein intake and it is
decreased in patients with a low protein intake or in patients with
liver disease.
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Plasma Urea
 Many renal diseases with various glomerular, tubular, interstitial or vascular damage
can cause an increase in plasma urea concentration.
 The reference interval for serum BUN of healthy adults is 5-39 mg/dl. Plasma
concentrations also tend to be slightly higher in males than females. High protein diet
causes significant increases in plasma urea concentrations and urinary excretion.
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 Measurement of plasma creatinine provides a more accurate
assessment than urea because there are many factors that affect
urea level.
 Nonrenal factors can affect the urea level (normal adults is level
5-39 mg/dl) like:
 Mild dehydration,
 high protein diet,
 increased protein catabolism, muscle wasting as in
starvation,
 reabsorption of blood proteins after a GIT haemorrhage,
 treatment with cortisol or its synthetic analogous
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Urinalysis
• Appearance - blood, colour, turbidity.
• Specific gravity - sticks measure ionic particles only, not glucose.
• pH - normally acidic, except after a meal.
• Glucose - the presence of glucose in urine may indicate increased
blood glucose, or tubular disorder.
• Proteinuria - the presence of protein in the urine may be caused by
glomerular leak, raised serum low-molecular weight proteins, Bence
Jones' proteins, myoglobulin, or protein of renal origin.
• Microscopy - urinary tract infection will show polymorphs with no
casts; acute glomerulonephritis will show cells and casts;
chronic glomerulonephritis shows little sediment.
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Imaging Tests
• Ultrasound
• This test uses sound waves to get a picture of the kidney. It
may be used to look for abnormalities in size or position of
the kidneys or for obstructions such as stones or tumors.
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• CT Scan
• This imaging technique uses contrast dye to picture the
kidneys. It may also be used to look for structural
abnormalities and the presence of obstructions.
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kidney Biopsy
• A biopsy may be done occasionally for one of the following
reasons:
1. to identify a specific disease process and determine
whether it will respond to treatment
2. to evaluate the amount of damage that has occurred in
the kidney
3. to find out why a kidney transplant may not be doing well
A kidney biopsy is performed by using a thin needle with a
sharp cutting edge to slice small pieces of kidney tissue for
examination under a microscope.
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Urine Tests
• Some urine tests require only a couple of tablespoonfuls of
urine. But some tests require collection of all urine produced
for a full 24 hours. A 24-hour urine test shows how much
urine your kidneys produce in one day. The test also can give
an accurate measurement of how much protein leaks from
the kidney into the urine in one day.
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MICROALBUMINURIA
• This is a more sensitive dipstick test, which can
detect a tiny amount of protein called albumin in
the urine.
• People who have an increased risk of developing
kidney disease, such as those with diabetes or high
blood pressure, should have this test if their
standard dipstick test for proteinuria is negative.
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Albuminuria-to-creatinine ratio (ACR).
• Albuminuria occurs when there are higher amounts of a type of
protein called albumin in the urine, It is a common marker of kidney
damage. The ratio of albumin-to-creatinine is recommended as the
best method to determine albuminuria.
• All patients with CKD should be tested for albuminuria at least
annually.
• You should also get tested if you are at risk for kidney disease (have
diabetes, high blood pressure, or family history of diabetes, high
blood pressure or kidney failure).
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