Download MBBS Renal Function Test Lecture PPT

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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 metabolism

are 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 synthesis

and formation of erythrocytes.

B. 1,25-Dihydroxycholecalciferol (calcitriol):

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The active form of vitamin D is finally produced in the

kidney. It regulates calcium absorption from the gut.

C. Renin:

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A proteolytic enzyme liberated by kidney, stimulates

the 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 a

molecular weight < 68,000, are passed into the
filtrate.

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? The glomerular filtrate is almost similar in

composition 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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v



The 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/min
INDICATION

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 procedure
CLASSIFICATION

I. GLOMERULAR FILTRATION CAPACITY TEST

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I. Clearance tests
II. Serum urea
III. Serum creatinine

II. GLOMERULAR

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FILTRATION

BARRIER

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INTEGRITY TEST

A. 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. Osmolality
D. 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 is
completely 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 equation

U 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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change



Vs GFR

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Substance only

Clearance = GFR

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Inulin

filtered

( No reabsorbtion

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No secretion)

Substance filtered

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Clearance < GFR

Urea

and reabsorbed

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Substance filtered

Clearance > GFR

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Creatinine

and 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 creatinine

clearance.
Urea clearance test

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? Urea clearance is defined as the volume (ml) of plasma

that 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 V

Cm =

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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formula

U 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 the
normal.

? 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 or

dietary 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 be

completely 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% of

normal ) indicate a decrease GFR reflecting
renal damage.

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? It is helpful in the early detection of functional

impairment 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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Disdvantages

1. 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 creatinine

will 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 is

determined by GFR.

? Normal adults have circulating level of approx. 1mg/l.

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? This is better indicator of renal function as compared to

creatinine 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 in

females)/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 DISEASE
2. Serum urea

? Urea is major nitrogenous end product of protein and

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amino acid catabolism, produced by liver and distributed
throughout 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 level

a) 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 synthetic

analogous
? 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 is

performed to differentiate between pre-renal and post-
renal azotemia

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? Pre-renal azotemia leads to increased urea levels, while

creatinine 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 muscle

mass

? Creatinine is filtered but not reabsorbed in kidney.

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? A small amount of creatinine is secreted into tubules

and 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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? Amiloride

injury

? 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 BARRIER

INTEGRITY 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 injury

before 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 become

more 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 damage
MICRO-ALBUMINURIA

? It

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is

also

called

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minimal

albuminuria

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or

paucialbuminuria.

? 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 damage


other proteins having high molecular weight

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like immunoglobulin are excreted into urine
TUBULAR PROTEINURIA occurs when the renal tubules
cannot reabsorb low molecular weight proteins

Tubular

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proteinuria

is ? This

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protein

pattern

associated with

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reveals protein bands in

? Drug toxicity

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the

i.

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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and

myoglobinuria.

? 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 damage


TUBULAR FUNCTION TEST

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? These tests are based on tubular reabsorption and

secretion 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 of

specific 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 be

counterbalanced 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 high

molecular 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 also

help to assess tubular function

? Plasma osmolality is 285-295 mOsm/kg.

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3. WATER DEPRIVATION TEST OR URINE

CONCENTRATION 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 morning

If 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 given

Hourly 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 volume
above 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 or

Urinary 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 determined
defects 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 of
sodium that gets
excreted in the urine
over

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the

total

filtered sodium by

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the kidney


URINE ANALYSIS

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URINE ANALYSIS