RENAL FUNCTION TEST
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DR. S. SHEKHAR
ASSOC. PROFESSOR
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DEPT. OF BIOCHEMISTRY
FUNCTIONS OF KIDNEY
1. Maintenance of homeostasis:
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The kidneys are responsible for the regulation of water,electrolyte & acid-base balance in the body.
2. Excretion of metabolic waste products:
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The end products of protein & nucleic acid metabolismare eliminated from the body. These include urea,
creatinine, creatine, uric acid, sulfate & phosphate
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3. Retention of substances vital to body:The kidneys reabsorb & retain several substances of
biochemical importance in the body e.g. glucose,
amino acids etc
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4. Hormonal functions:A. Erythropoietin:
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A peptide hormone, stimulates haemoglobin synthesisand formation of erythrocytes.
B. 1,25-Dihydroxycholecalciferol (calcitriol):
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The active form of vitamin D is finally produced in thekidney. It regulates calcium absorption from the gut.
C. Renin:
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A proteolytic enzyme liberated by kidney, stimulatesthe formation of angiotensin II which, in turn, leads to
aldosterone production.
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Angiotensin II & aldosterone hormones involved in
the regulation of electrolyte balance.
URINE FORMATION
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? Nephron is the functional unit of kidney.
? Each kidney is composed of approximately one million
nephrons.
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? Nephron, consists of a Bowman's capsule (with blood
capillaries), proximal convoluted tubule (PCT), loop of
Henle, distal convoluted tubule (DCT) & collecting
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tubule.? About 1200 ml of blood (650 ml plasma) passes through
the kidneys, every minute.
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? About 120-125 ml is filtered per minute by the
kidneys & this is referred to as glomerular filtration
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rate (GFR).? With a normal GFR (120-125 ml/min), the glomerular
filtrate formed in an adult is about 175-180 litres/day,
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out of which only 1.5 litres is excreted as urine.? More than 99% of the glomerular filtrate is
reabsorbed by the kidneys.
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? Urine formation basically involves two steps
glomerular filtration & tubular reabsorption.
Glomerular filtration
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? This is a passive process that results in the
formation of ultra filtrate of blood.
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? All the (unbound) constituents of plasma, with amolecular weight < 68,000, are passed into the
filtrate.
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? The glomerular filtrate is almost similar incomposition to plasma except proteins and cell.
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Tubular reabsorption? The renal tubules (PCT, DCT & collecting
tubules) retain water & most of the soluble
constituents of the glomerular filtrate by
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reabsorption.? This may occur either by passive or active
process.
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Renal threshold? There are certain substances in the blood whose
excretion in urine is dependent on their concentration.
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? Such substances are referred to as threshold substances.
? At the normal concentration in the blood, they are
completely reabsorbed by the kidneys.
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? But when their blood levels are elevated beyond the
normal range exceeding the tubular reabsorption capacity
the excesss is excreted in urine.
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? The renal threshold of a substance is defined as its
concentration in blood (or plasma) beyond which it is
excreted into urine.
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vThe renal threshold for
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Glucose --------180 mg/dl
Ketone bodies--- -3 mg/dl
Calcium ----------10 mg/dl
Bicarbonate ------ 30 mEq/l
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vTubular maximum (Tm):? The maximum reabsorptive capacity of the
renal tubules to absorb a particular substance.
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? Tubular maximum for glucose is 375 mg/minINDICATION
1. Detection of renal damage
2. Assessment of extent of renal damage
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3. Monitoring the progression of renal damage /disease
4. Monitoring and adjusting the dose of
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potentially renal toxic drugs
5. Before giving renal excretory contrast in some
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diagnostic procedureCLASSIFICATION
I. GLOMERULAR FILTRATION CAPACITY TEST
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I. Clearance testsII. Serum urea
III. Serum creatinine
II. GLOMERULAR
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FILTRATION
BARRIER
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INTEGRITY TESTA. Proteinuria
B. Hematuria
C. Urine protein electrophoresis
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III. TUBULAR FUNCTION TESTS
A. Reabsorption test
B. Renal concentration test/ water deprivation test
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C. OsmolalityD. Specific Gravity
E. Urine dilution test
F. Sodium Excretion Test
G.Ammonium Chloride loading test or urinary
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acidification test
IV. COMPLETE URINE ANALYSIS
I. GLOMERULAR FILTRATION CAPACITY TEST
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? It measures the total filtration occuring at glomerulus.
? These indicates the percentage, or fraction of the total
nephron that are functioning.
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A decrease in 50% filtration capacity
indicates that about half of the total nephrons have
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lost their function.
1. RENAL CLEARANCE TESTS
? To assess the rate of glomerular filtration & renal
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blood flow.
? "The renal clearance of a substance is defined as the
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volume of plasma from which the substance iscompletely cleared by the kidneys per minute."
? This depend on
- plasma conc. of the substance & it's
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excretary rate
- GFR
- Renal plasma flow
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Renal Clearance Tests? The GFR (Normal = 120 ml/minute )
? Usually equal to clearance of that substance and is
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calculated by the following equationU x V
C =
P
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Where, C = Clearance of the substance (ml/mt)U = Conc.of substance in urine (mg/L)
P = Conc.of substance in plasma (mg/L)
V = Vol.of the urine passed per minute
Renal metabolic
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Clearance Value
Example
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changeVs GFR
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Substance only
Clearance = GFR
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Inulinfiltered
( No reabsorbtion
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No secretion)
Substance filtered
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Clearance < GFRUrea
and reabsorbed
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Substance filtered
Clearance > GFR
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Creatinineand secreted
A. Urea clearance test
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? Urea is the end product of protein metabolism.? After filtered by the glomeruli, it is partially
reabsorbed by the renal tubules.
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? So, Urea clearance is less than the GFR & it is
influenced by the protein content of the diet.
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? Urea clearance is not as sensitive as creatinineclearance.
Urea clearance test
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? Urea clearance is defined as the volume (ml) of plasmathat would be completely cleared of urea per minute.
? If the output of urine is more than 2 ml per minute.
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[ V > 2ml/min]
This is referred to as maximum urea clearance & the
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normal value is around 75 ml/min
? It is calculated by the formula:
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U X VCm =
P
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? Cm=Maximum urea clearance.
? U = Urea concentration in urine (mg/dl).
? V = Urine excreted per minute in ml.
? P = Urea concentration in plasma.
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Standard urea clearance
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? The urea clearance drastically changes when the
volume of urine is less than 2 ml/min.
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[ V < 2ml/min]
? This is known as standard urea clearance (C) & the
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normal value is around 54 ml/min
? Standard urea clearance is calculated by a modified
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formulaU X V
Cs =
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P
? A urea clearance value below 75 % of the normal
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indicates renal damage.? Usually blood urea level start rising only when
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the clearance value falls below 50% of thenormal.
? Urea clearance values may not always coincide
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with blood urea level.? Urea is reabsorbed by the renal tubule and
hence tubular function affects urea clearance.
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? Normal level of blood urea: 20-40 mg/dl
B. Creatinine clearance test
? Creatinine is an excretory product derived from
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creatine phosphate in muscle.
? The excretion of creatinine is rather constant &
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is not influenced by body metabolism ordietary factors.
? Creatinine is filtered by the glomeruli & only
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marginally secreted by the tubules.
? Creatinine clearance may be defined as the
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volume (ml) of plasma that would becompletely cleared of creatinine per minute.
Procedure:
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? In the traditional method, creatinine content of a 24 hr
urine collection & the plasma concentration in this
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period are estimated.
? The creatinine clearance (C) can be calculated as
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follows:U X V
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Ccr = P
U = Urine concentration of creatinine.
V = Urine output in ml/min (24 hr urine volume
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divided by 24 x 60)P = Concentration of creatinine.
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? The normal range of creatinine clearance is
around 120-145 ml/min.
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? A decrease in creatinine clearance ( <75% ofnormal ) indicate a decrease GFR reflecting
renal damage.
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? It is helpful in the early detection of functionalimpairment of kidney and also for monitoring
the patients with renal insufficiency
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? In older people, the clearance is decreased.Creatinine clearance test as a GFR marker
Advantages
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Disdvantages1. It is not affected by diet or 1. Secreted by tubule, so
exercise
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clearance > GFR
2. Extrarenal factors will rarely
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interfere.2. Overestimate GFR by
10-20 ml/min
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3. Conversion of creatine
phosphate to creatinine is 3. Very early stages of
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spontaneous, non-enzymatic.decrease in GFR (50-70
4. As the production is
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ml/min) may not be
continuous, the blood level
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identified by creatininewill not fluctuate. Blood
clearance (creatinine
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may be collected at any time.
blind area).
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Relation between GFR AND Plasma Creatinine
C. Inulin Clearance Test
? Method of choice when accurate determination
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of GFR is required.
? Inulin is polysacharide of Fructose.
? Freely filtered by glomerulus not reabsorbed not
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secreted or metabolically altered by the renal
tubule.
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? Normal value : 120 ml/mt.? Disadvantages :need for its
IV adminstration
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technically difficulty of
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analysis
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D. Cystatin C as a filtration marker? It is a LMW nonglycosylated protein produced at a
constant rate by all nucleated cells in the body,
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? Freely filtered by the glomeruli, and totally reabsorbed
by the renal tubules.
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? It is not secreted, by the tubules. Thus, its plasma level isdetermined by GFR.
? Normal adults have circulating level of approx. 1mg/l.
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? This is better indicator of renal function as compared tocreatinine in early stages of GFR impairment as it is
independent of age,gender,body composition & muscle
mass.
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E. Estimated GFR (eGFR)? A simpler technique of estimating creatinine
clearance and there by GFR is by using serum
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creatinine level.? This would eliminate the need for timed urine
collections.
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? A commonly used formula is Cockcroft-Gault
equation.
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? Ccr = (140 ? age in years) ? weight in Kg (0.85 infemales)/72 ? Pcr in mg/dL
? The factor 0.85 is used in females assuming that they
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have 15% less muscle mass.
MDRD (Modification of Diet in Renal Disease) Formula
? This equation directly estimates GFR.
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? The estimated GFR (eGFR) (mL/min/1.73m2)eGFR = 186 ? (Creatinine/88.4) -1.154 ? (Age) ?0.203 ?
0.742 (if female)
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? Estimates GFR adjusted for body surface area.
? Designed for use with laboratory creatinine test.
? Is more accurate than creatinine clearance measured from
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24-hour urine collections or estimated by the Cockcroft-Gault formula.
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GRADING OF CHRONIC KIDNEY DISEASE2. Serum urea
? Urea is major nitrogenous end product of protein and
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amino acid catabolism, produced by liver and distributedthroughout intracellular and extracellular fluid.
? Urea is freely filtered by the glomeruli
? 40-70% of it is passively absorbed by diffusion into
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renal tubules depending upon urine flow rate.
? The reference interval - 10-40 mg/dl
? High protein diet causes significant increases in plasma
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urea concentrations
? Many renal diseases with
various glomerular, tubular,
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interstitial or vascular damage can cause an increase
in plasma urea concentration
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? Nonrenal factors can affect the urea levela) Mild dehydration,
b) high protein diet,
c) increased protein catabolism,
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d) muscle wasting as in starvation,e) reabsorption of blood proteins after a GIT
haemorrhage,
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f) treatment with cortisol or its syntheticanalogous
? States associated with
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elevated levels of urea in blood are
referred to as uremia or azotemia
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? Causes of plasma urea elevations:
Prerenal: renal hypoperfusion
Renal: acute tubular necrosis
Postrenal: obstruction of urinary flow
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? Parallel determination of urea and creatinine isperformed to differentiate between pre-renal and post-
renal azotemia
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? Pre-renal azotemia leads to increased urea levels, whilecreatinine values remain within the reference range.
? In post-renal azotemias both urea and creatinine levels
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rise, but creatinine in a smaller extent
BLOOD UREA NITROGEN (BUN)
? Sometimes, blood urea level is expressed as blood urea
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nitrogen (BUN)
? BUN is the nitrogen content of urea present in blood
? Molecular weight of urea is 60 in which the
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contribution of nitrogen atoms is 28
? Therefore, BUN equals blood urea multiplied by 28/60
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i.e. nearly 0.47? The normal range of BUN is 10-20 mg/dl
? A rise in nitrogen content of blood is called azotaemia
Serum creatinine
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? Creatinine is a breakdown product of creatine
phosphate in muscle, and is usually produced at a
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fairly constant rate by the body depending on musclemass
? Creatinine is filtered but not reabsorbed in kidney.
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? A small amount of creatinine is secreted into tubulesand its secretion is increased with the increasing level
of plasma creatinine.
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? Normal range is 0.8-1.3 mg/dl in men and 0.6-1 mg/dl
in women
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? Not increased above normal until GFR<50 ml/min .Increased serum creatinine
? Impaired renal function
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vDrugs:? Anabolic steroid users
? Probenecid
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? Vary large muscle mass:
? Cimetidine
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body builders,? Triamterene
acromegaly patients
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? Trimethoprim
? Rhabdomyolysis/crush
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? Amilorideinjury
? Athletes taking oral
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creatine
Determination of serum creatinine gives a useful
indication of the degree of renal failure
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II. GLOMERULAR FILTRATION BARRIERINTEGRITY TEST
Glomerulus acts as a selective filter of the blood passing
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through its capillaries
A. PROTEINURIA
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? Proteinuria is the first sign of glomerular injurybefore any decrease in GFR.
? The glomeruli of kidney are not permeable to
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substances with molecular weight more than 69,000
& plasma proteins are absent in normal urine
PROTEINURIA
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? When glomeruli are damaged or diseased, they becomemore permeable & plasma proteins may appear in urine.
? The smaller molecules of albumin pass through damaged
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glomeruli more readily.
? Albuminuria is always pathological
If total protein excretion > 150 mg/day
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Or
Albumin excretion > 30 mg/day
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Indicative of glomerular damageMICRO-ALBUMINURIA
? It
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isalso
called
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minimal
albuminuria
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orpaucialbuminuria.
? It is an early indicator of onset of nephropathy due to
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microvascular glomerular damage.
? Micro albuminuria is an early indication of nephropathy
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in patients with diabetes mellitus & hypertension.? It is identified, when small quantity of albumin (30-300
mg/day) is seen in urine.
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? It is also expressed as albumin creatinine ratio. Albumin
creatinine ratio ? 30-300mg albumin /gm of creatinine
URINARY PROTEIN ELECTROPHORESIS
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? Urine protein electrophoresis separates the proteins
according to charge and allows classification of the type
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of renal injury.? Protein patterns are interpreted and classified as
glomerular, tubular, or mixed patterns
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In minimal glomerular damage
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Low molecular weight protein such as albumin,1- AT, and transferrin are excreted
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In severe glomerular damageother proteins having high molecular weight
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like immunoglobulin are excreted into urineTUBULAR PROTEINURIA occurs when the renal tubules
cannot reabsorb low molecular weight proteins
Tubular
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proteinuria
is ? This
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proteinpattern
associated with
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reveals protein bands in
? Drug toxicity
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thei.
aminoglycosides,
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? alpha 2 region (alpha 2
ii. cephalosporins,
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microglobulin,retinol
binding protein), and
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iii. Cyclosporine
? one band in the beta 2
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?Pyelonephritis,
region
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(beta
2
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?Interstitial nephritis,
microglobulin)
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?
Renal vascular disease,
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and?
Transplant rejection.
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Overflow proteinuria? It is caused by high plasma protein
concentrations that exceed the reabsorptive
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capacity of the tubules.? Common examples include Bence-Jones
Proteins
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(multiple
myeloma)
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andmyoglobinuria.
? In hemolytic conditions, hemoglobin can
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appear in urine (hemoglobinuria)
B. HEMATURIA
? An earliest sign of glomerular damage before the
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overt decrease in GFR.
? Intact glomerulus does not allow the passage of RBC.
When severe glomerular damage
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RBC leakage occurs
? Detection of microscopic hematuria or RBC casts
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confirm glomerular damageTUBULAR FUNCTION TEST
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? These tests are based on tubular reabsorption andsecretion function of kidneys.
? The tubular epithelial cells of nephrons are highly
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specialized structure, which selectively reabsorb
water and some substances and secrete other.
1. Specific gravity of urine
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? The simplest test of tubular function is the measurement ofspecific gravity of urine by a urinometer.
? Normal 1.015-1.025
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? This is an indication of osmolality.? Incase of proteinuria S.G. elevated.
? Earliest manifestation of renal disease may be difficulty in
concentrating the urine.
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? Sp.gr.-- excessive water intake, ch.nephritis, Diabetes
Insipidus
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? Sp.gr.-- diabetes mellitus, nephrosis, Ch.Renal failure.? Fixed sp.gr. at 1.010 isosthenuria -- earliest
manifestation of tubular disease / chronic renal failure.
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? A defect in concentrating capacity is termed
hyposthenuria.
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? The inability to excrete the waste products may becounterbalanced by large urine output.
? Thus the earliest manifestation of the renal disease
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may be difficulty in concentrating urine.
2. Urine Osmolality
? Osmolality of urine varies from 50 mosm/kg in
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condition of excessive fluid intake to 1200 mosm/kg in
low fluid intake.
? Random urine sample = 850-900 mosm/kg.
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? It is found that the urine (without any protein or highmolecular weight substance) with an osmolality of 800
mosm/kg has a specific gravity of 1.020
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? Therefore, measurement of urine osmolality will alsohelp to assess tubular function
? Plasma osmolality is 285-295 mOsm/kg.
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3. WATER DEPRIVATION TEST OR URINECONCENTRATION TEST
? 99% of water of glomerular filtrate is reabsorbed during
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its passasge through different segment of renal tubule.
Fluid intake is withheld overnight preferably 18 hours
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osmolality of 1st urine sample in the morningIf osmolality > 850 mosmol/kg , Sp.Gv- 1.022
Renal concentrating ability is normal/good
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? In low ADH activity ( hypothalmic / pituitary
disorder) or nephrogenic diabetes insipidus (lack of
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response to ADH)Osmolality is low and rarely exceeds 300 mosm/kg
(Sp. Gr. 1.010)
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4. Urine dilution test? A normal kidney produce a dilute urine following excessive
water intake.
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After an overnight fast and fluid deprivation
Bladder is emptied at 7 am and water load (1200 ml over
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the next 30 min) is givenHourly urine samples are collected for next four hours
The specific gravity of at least one sample should fall to
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1.003 and osmolality to 50 mOsm/kg
? Normal person will excrete all the water load with in
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4 hours
? Kidneys which are severely damaged cannot excrete a
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urine of lower specific gravity than 1.010 or a volumeabove 400 ml in this time.
? This test is more sensitive and less harmful than
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concentration test? The test should not be done if there is oedema or renal
failure; water intoxication may result
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5. Ammonium chloride loading test orUrinary Acidification test
? It is indicated in unexplained hyperchloremic
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metabolic acidosis
? Acidification defects may occur due to generalized
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tubular defects or due to genetically determineddefects in ion pumps
? Enteric coated capsules containing ammonium
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chloride at a dose of 0.1 g / kg body wt is given? In the liver, NH3 is converted to urea and HCl is
produced which is excreted by kidney.
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? Urine is collected hourly from 2 to 8 hours after
ingestion.
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? At least one sample should have a pH of 5.3
? In type I distal renal tubular acidosis, urinary pH
rarely falls below 6 and never falls below 5.3.
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? Liver disease is a contraindication to perform this
test.
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FRACTIONAL EXCRETION OF SODIUM
It is a measure of
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the percentage ofsodium that gets
excreted in the urine
over
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thetotal
filtered sodium by
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the kidneyURINE ANALYSIS
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URINE ANALYSIS