RFT

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• Renal Function Tests

M.PRASAD NAIDU Msc Medical Biochemistry, Ph.D
Research scholar.
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• Kidney Functions
• 1. Urine formation
• 2. Regulation of fluid and electrolyte balance
• 3. Regulation of acid-base balance
• 4. Excretion of waste products of nitrogen
  metabolism
• 5. Hormonal function
• 6. Protein conservation

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• Urine formation
• Normal glomerular filtration rate (GFR) is
  approximately 125ml/min.
• About 190 liters of glomerular filtrate is
  formed daily(24Hours).
• Most of it is reabsorbed(99) except 1 to 1.5
  liters excreted as urine.

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• In PCT
• 60 to 80 of glomerular filtrate is reabsorbed.
• Na , Cl- , K , HCO3- , glucose, amino
  acids are reabsorbed.
• 90 of H is secreted.
• Renal threshold for glucose 180mg/dl.
• TMG - 350 mg/minute
• Renal threshold for bicarbonate 30mequ/L.

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• Passive reabsorption of water, urea, chloride
  also occurs.
• Tubular secretion Potassium, H ions , ammonia
  , uric acid, drugs.

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• Loop of Henle Concentration of Urine
• DCT
• Aldosterone increases sodium reabsorption and
  excretion of potassium.
• Ammonia is secreted in the DCT buffers H
  ions secreted as ammonium ions.
• ADH acts on DCT increases reabsorption of
  water.

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• Excretion of Waste Products
• The End products of protein and nucleic acid
  metabolism like urea, creatinine , sulphate ,
  uric acid, phosphate are excreted by the kidney.
• Retention of useful compounds
• Glucose, aminoacids, sodium etc are reabsorbed

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• Protein Conservation
• Normal urine contains lt 200mg of protein / 24
  hour urine.
• Most of the filtered proteins are reabsorbed by
  PCT.
• Note Albumin excretion lt 20mg/24hours urine.

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• Hormonal Functions
• Erythropoietin A peptide hormone
• stimulates hemoglobin synthesis and formation of
  erythrocytes.
• Calcitriol - (1,25 DHCC)
• Active form of vitamin D

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• Renin
• A Proteolytic enzyme secreted by kidney
• Which converts angiotensinogen to angiotensin
  II.
• Which in turn increases the secretion of
  aldosterone

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• Tests for Glomerular Function
• Clearance Tests
• Clearance may be defined as volume of plasma in
  ml which contains the amount of substance which
  is excreted in urine in 1minute.
• UV U Substance in urine mg/100ml
• P P Substance in plasma
  mg/100ml
• V Volume of urine ml/mt

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• normal Caluculation
• eg Urea UV X 100 X 1.73
• P 75 BS
• Inulin clearance 125 ml/mt (110 135)
• Urea clearance 75 ml/mt (60 90)
• Creatinine clearance 120 ml/mt (110 130)

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• Inulin clearance 125ml/mt
• Inulin is a plant polysaccharide contain
  fructose.
• Inulin has to be given I.V to perform the test.
• Inulin clearance test is called gold standard.
• Theoretically most ideal test because it is not
  secreted into the renal tubule and it is not
  reabsorbed by the renal tubules.
• Inulin is excreted as such through urine.

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• But the test is cumbersome, needs I.V
  administration of inulin.
• Imp This test is not used routinely.

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• Urea clearance 75ml/mt
• Urea is the end product of protein metabolism.
• after being filtered by the glomeruli, it is
  partially reabsorbed by the renal tubules.
• Its clearance is lt GFR.
• It is also influenced by dietary protein
  content.
• Blood urea levels tend to increase only when
  urea clearance value falls below 50 normal
• Not an Ideal test.

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• Creatinine Clearance Test 120ml/mt
• Most commonly done test
• Creatinine is a waste product derived from
  creatine ( present in muscle).
• Creatinine formation and excretion mainly
  depends upon muscle mass.
• Not influenced by dietary factors.
• The value of creatinine clearance is very close
  to GFR.

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• Procedure
• In the traditional test 24 hour urine is
  collected and creatinine concentration estimated
  both in urine and serum and clearance is
  calculated.
• Modified Procedure
• Urine is collected for 1 hour after giving
  water.
• Volume of urine is noted.
• Serum creatinine and urine creatinine are
  estimated and clearance is calculated.

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• The creatinine clearance is lower in women(less
  muscle mass).
• Normal serum creatinine levels 0.7 to 1.4mg/dl.
• Serum creatinine levels increase beyond the
  normal range only when more than 50 of
  Glomerular Function is lost.

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Renal tubular Function Tests
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Normal urine specific gravity -1.015 to
1.025. SPECIFIC GRAVITY is tested by
URINOMETER. Specific gravity increased in
diabetesmellitus, excessive persipration. Specifi
c gravity decreased in diabetes insipidus
,excessive water intake , chronic
nephritis.
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The simplest test for tubular function is the
measurement of the specific gravity of
urine. Specific gravity depends on concentration
of solutes . Osmolality depends on number of
osmotically active molecules.
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• Osmolality
• The concentration of a solution expressed as the
  total number of solute particle per kilogram.
• Osmolarity
• the concentration of a solution expressed as the
  total number of solute particles per liter.

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In moderate forms of kidney damage , blood level
of urea and creatinine may be within normal
limits. The inability to excrete the waste
products may be counterbalanced by large urine
output. Thus ,the earliest manifestation of renal
disease may be DIFFICULTY IN CONCENTRATING THE
URINE.
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Concentration tests Principle based on the
ability of the kidneys to concentrate urine, and
based on measuring specific gravity of urine.
Simple bedside procedure . Easy to perform
Tests are conducted either under conditions of
restricted fluid intake or
By inhibiting diuresis by injection of ADH.
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Procedure for concentration tests Patient is not
allowed to take food or water after a meal at
6pm. Next day at 7am bladder is emptied and
specimen is discarded. A second specimen is
collected at 8 am and specific gravity is
measured. Adequate renal function specific
gravity 1.022 and osmolality exceeds850
mosm/kg. In renal tubular disease urine shows a
fixed specific gravity around 1.010 (300mosm/kg)
as the tubules loose their concentrating capacity.
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ADH test ( concentration test) Effectiveness of
ADH decreases with IMPAIRED tubular
function. Procedure 5 units of ADH injected.
Hourly samples of urine collected for next 24
hrs and tested for specific gravity. At least one
sample should have a specific gravity MORE THAN
1.020 and osmolality 800mosm/kg.
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Measurement of osmolality Normally urine
osmolality varies from 80 mosm/kg to 1200 mosm/kg
. Normal plasma osmolality is 285 300
mosm/kg. Simultaneous measurements of plasma and
urine osmolality and calculation of ratio of
urine /plasma is more useful. Normally the ratio
varies from 3 4.5 . Osmolality is measured with
an osmometer.
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Urine Dilution tests Principle the ability of
the kidneys to eliminate water is tested by
measuring the urinary output after ingestion of a
large volume of water. Procedure Patient is not
allowed to take water after midnight. Bladder is
emptied at 7 am. Water load is given -1200ml over
next 30 minutes. Urine samples are collected
hourly over next four hrs.
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Volume , specific gravity and osmolality of each
sample measured . A noraml person will EXCRETE
ALMOST ALL THE WATER LOAD WITHIN FOURS HOURS and
specific gravity of at least ONE SAMPLE SHOULD
FALL to 1.003 and osmolality to 50 mosm/kg . The
test is MORE SENSITIVE .
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Urine volume,appearance ,odour , colour Urine
specific gravity Urine pH Urine osmolality Blood
urea Serum creatinine Clearance tests
creatinine clearancesss Abnormal constituents
proteins, blood , reducing sugars , ketone bodies
, bilesalts and
bile pigments.
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• Test for Tubular Function PSP test (Phenol
  sulfo phthalein)
• Give 600ml of water.
• Inject 6mg of dye I.V.
• Urine 15 mt 35 excreted
• In 2 hours 70 of dye eliminated through urine.
• This test indicates secretary function of
  tubules.
• Less than 50 of dye elimination in 2 hours.
• Indicated tubular defect.

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• Tubular function test
• PAH clearance 700ml/mt

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• Glomerular filtration rate(GFR)
• The rate in milliliters per minute at which
  plasma substances are filtered through the
  glomeruli into thel proximal tubule.
• Renal threshold
• The plasma concentration of a substance above
  which it will be present in urine.
• Specify gravity
• The ratio of the weight in grams per milliliter
  of a body fluid compared with water.

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• Titratable acid
• The combination of hydrogen ion with phosphate
  present in final urine.
• Urine
• The aqueous liquid and dissolved substances
  excreted by the kidney.

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THANK YOU