UROGENITAL SYSTEM

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UROGENITAL SYSTEM Biochemical Investigations of
Urogenital Diseases MBBS Year-2 Lecture 26
September 2002 830 - 930 am Dr. Sidney Tam Hon
Clinical Professor Department of Pathology The
University of Hong Kong
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The KIDNEY has 3 major functions

• Regulation of water, electrolyte and acid-base
  balance
• Excretion of waste products of intermediary
  metabolism, e.g., urea, creatinine, uric acid,
  phosphate, sulphate and organic acids
• Production and elaboration of hormones, e.g.,
  renin, erythropoietin, 1,25 dihydrocholecalciferol
  

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Renal Blood Flow (RBF) 20 Cardiac
Output 1200 mL/min Glomerular Filtrate
Rate 125 mL/min (Filtration Fraction 10) 18
L/day Urine Formation 1 mL/min 1.5 L/day
99 H2O in glomerular ultrafiltrate reabsorbed by
the kidney 65 occurs in the proximal renal
tubules accompanied by Na and Cl- reabsorption
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Obligatory Water Loss Urea, SO42-, PO42-
other waste products of metabolism 550
mOsm/day Maximal Urinary Concentration
attainable 1400 mOsm/L Therefore
550 mOsm/day Minimal Volume of Urine Water
----------------------- ? 400 mL/day
1400 mOsm/L Azotaemia is inevitable with daily
U.O. lt 400 mL
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Assessment of Glomerular Function

• The capacity of the kidneys to filter plasma at
  the glomeruli can be assessed by measuring the
  Creatinine Clearance, which approximates to the
  GFR
• Plasma Creatinine concentration is an insensitive
  index of renal function, as it may not appear to
  be elevated until the GFR has fallen by 50
• Once the plasma Creatinine concentration is
  elevated, changes in its level reflect changes in
  GFR

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Glomerular Filtration Rate (GFR) 1

• GFR is the volume of glomerular filtrate (an
  ultrafiltrate of plasma) produced by both kidneys
  (110 - 140 mL/min in adults).
• Maintenance of a normal GFR depends on an
  adequate number of nephrons with intact
  glomerular function and a normal renal perfusion
• Destruction of nephrons or reduced renal blood
  flow lead to a fall in GFR resulting in the
  retention of metabolic wastes, reflected by
  raised Creatinine and Urea levels in plasma

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Glomerular Filtration Rate (GFR) 2

• Measuring the concentration of a substance which
  is freely filtered by glomeruli but not
  reabsorbed nor secreted by the tubules (e.g.,
  inulin) in a timed collection of urine and a
  concomitant plasma sample enables the estimation
  of GFR
• Creatinine Creatinine (CrCl) approximates to GFR,
  and is commonly used in most clinical settings in
  lieu of other more accurate but cumbersome
  assessments of GFR, e.g., inulin clearance,
  99Tc-DTPA scintigraphy, 51Cr-EDTA clearance.

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Clearance Clearance as an estimation of GFR
Creatinine Clearance (Cr Cl) is calculated as
follows Ucr x V Cr Cl
---------------- Pcr Ucr Urine
concentration of Creatinine Pcr Plasma
concentration Creatinine V Volume of urine
produced over a fixed period (usually a
24-hour collection) Creatinine Clearance is
usually expressed in mL/min
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CREATININE CLEARANCE (Cr Cl) (Cockcroft Gault,
1976) (140 - Age) x Body
Weight Cr Cl ( mL / min ) -------------------
---------------------- x 0.85 (for female)
814 x Plasma Creatinine
Age Year Body Weight Kg Plasma
Creatinine conc mmol / L Correlates with
measured values of GFR provided that i. Plasma
creatinine is not within normal
range ii. Renal impairment is not
severe iii. No inhibition of tubular secretion
of creatinine by medications
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Plasma CREATININE and UREA

• Plasma concentrations of Creatinine and Urea are
  used as convenient but rather insensitive
  measures of glomerular function - their levels
  may remain within reference ranges in the
  presence of a significant reduction of GFR
• CREATININE
• Creatinine is an end product of muscle metabolism
  that is released into circulation at a relatively
  constant rate
• Creatinine is freely filtered by glomeruli and
  not reabsorbed by renal tubules, but there is
  some tubular secretion the degree of which
  increases with rising plasma levels - Creatinine
  Clearance over estimates GFR

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UREA Waste product of Amino Acid
metabolism Excretory Load dependent on amino
acid and protein Intake as well as Net Body
Protein Metabolism Filtered freely by the
Glomeruli and Diffuse back into the Renal Tubules
by a Passive process Clearance dependent on
Urine Flow Rate
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Plasma UREA is a poor indicator of GFR
because 1. ? production (low protein intake) can
lower the plasma urea sufficiently to enable a
normal plasma level to be associated with
significant renal insufficiency 2. GFR has to
drop 40 before the plasma urea begins to
rise 3. ? production (eg. high protein intake)
in the face of minor degrees of renal impairment
can result in disproportionately high plasma
urea
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Conditions Affecting UREA Independent of GFR

? UREA ? UREA High Protein Diet Liver
Disease Gastrointestinal Bleeding Malnutrition
Tissue Trauma Glucocorticoids
Tetracycline
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Conditions Affecting CREATININE Independent of
GFR
Condition Mechanism Spurious or True
Elevation Ketoacidosis Non creatinine
chromogen Cefoxitin, Cephalothin Non creatinine
chromogen Ingested cooked meat Gastrointestinal
absorption of creatinine Drugs (aspirin,
cimetidine Inhibition of tubular creatinine
secretion trimethoprim, amiloride triamterene,
spironolactone) Decrease Increasing
age Physiological ? in muscle mass Cachexia Path
ological ? in muscle mass
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Although Plasma CREATININE directly reflects
GFR, it is not always a good indicator of this
parameter because 1. Plasma level is dependent
on muscle mass 2. Creatinine secretion by the
proximal tubule increases as GFR decreases some
drugs (eg. cimetidine) interfere with this
secretion 3. Various substances interfere with
the Jaffe Reaction (commonly employed) assay
causing positive and negative bias (eg.
acetoacetate, cephalothin, bilirubin) 4. Dietary
factors e.g., roasted meat contain significant
amount of creatinine and ingestion of these can
raise the plasma level temporarily
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Assessment of Renal Tubular Function

• Renal tubules are involved in the formation of a
  concentrated urine and handling of acid load that
  is normally produced from the intermediary
  metabolism of the body
• Abnormality of the renal tubules can be detected
  by
• Osmolality measurements in plasma and urine,
  water deprivation test
• Inability to handle an acid load (acid-loading
  test)
• Specific proteinuria and tubular enzymes
• Presence of abnormal aminoaciduria and other
  compounds normally reabsorbed by the renal
  tubules (e.g., Fanconi syndrome)

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Urine and Plasma Osmolality

• Normal kidney can produce urine at a wide range
  of concentrations with osmolality between 50 -
  1400 mmol/kg
• As renal tubules lose their ability to absorb
  water and retain or secrete other substances,
  urine begins to resemble the plasma ultrafiltrate
• Because of the variation in urinary concentration
  with hydration and volume, a random Urine
  Osmolality (Uosm) has little diagnostic value
  unless correlated with the clinical state
• In patient suspected of diabetes insipidus, an
  overnight urine osmolality gt 600 mmol/kg or gt 2 x
  concomitant plasma Osmolality practically
  excludes the diagnosis

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Renal Tubular Acidosis (RTA)
A group of diverse disorders in which the kidney
is unable to acidify the urine normally The
tubular defects may be acquired or
hereditary Biochemically characterized
hyperchloraemic metabolic acidosis with a normal
anion gap and often a low plasma potassium level
a urine pH gt 5.3 in the presence of metabolic
acidosis Type 1 defective H ion secretion in
the distal tubule Type 2 reduced capacity of the
proximal tubule to conserve bicarbonate An Acid
Loading Test may be required to establish the
diagnosis
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Acute Renal Failure (ARF)
Definition Acute renal failure (ARF) is a
syndrome characterized by rapid (hours to weeks)
decline in glomerular filtration rate (GFR) and
retention of nitrogenous waste products such as
blood urea nitrogen and creatinine. Brenner
Rector, The Kidney, 6th ed
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Acute Renal Failure (ARF) These may be classified
according to aetiology as Pre-renal (impaired
renal perfusion), and resulting in pre-renal
azotaemia - a rapidly reversible form of ARF.
Post-renal (obstruction to urinary flow), and
resulting in post-renal azotaemia - also a
rapidly reversible form of ARF. Intrinsic renal
(structural damage to the kidney), and resulting
in acute intrinsic renal failure - a form of ARF
which is not rapidly reversible and may even be
progressive. Both pre- and post-renal causes of
ARF have the potential for causing structural
damage to the kidney if left untreated.
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CAUSES OF ACUTE INTRINSIC RENAL FAILURE 1. Acute
Tubular Necrosis Post-ischaemic,
Nephrotoxic 2. Acute Interstitial Nephritis Drug
Hypersensitivity Infection 3. Gram -ve
Sepsis 4. Postpartum Haemorrhage 5. Renal Artery
Occlusion (bilateral) 6. Acute Glomerulonephritis
70 of ATN have more than one underlying
causes Some ATN patients, particularly those
with nephrotoxic injury, are non-oliguric
initially
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Acute tubular necrosis (ATN) a potentially (but
not rapidly) reversible form of acute renal
failure involving structural damage to the
tubules and a consequential reduction in
glomerular filtration rate (GFR). Recovery
usually takes several weeks even when the cause
is removed.
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• ARF Biochemical Investigations
• P - Creatinine (muscle)
• P - Urea (protein catabolism)
• P - Osmolality
• P - K (life threatening if substantially
  increased)
• U - Na
• U - Creatinine
• U - Urea
• U - Osmolality
• Creatinine Clearance (CrCl)
• U - Sediment
• Also tests for decreased effective circulating
  volume,
• e.g. haematocrit

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Differentiation between PRA and ATN Pre-Renal
Acute Tubular Laboratory Test
Azotaemia Necrosis P- Urea / Creatinine
ratio gt 60 lt 40 Ur Sodium (mmol/L) lt 20 gt
40 Ur Osmolality (mmol/kg) gt 500 lt 350 Ur / P
Creatinine ratio gt 40 lt 20 Fractional excretion
of lt 1 gt 2 filtered Sodium (FENa) Urine
Sediment Normal or Brown occasional
granular granular casts casts, cellular
debris
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FRACTIONAL EXCRETION Fractional Excretion of a
substance X (Fex) is that portion of the total
amount filtered by the glomeruli which is
finally excreted in the urine Ux . Pcr FEx
-------------- x 100 Px . Ucr
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Fractional Excretion of Sodium
FENa Na excreted / Na filtered clearence
for Na / clearence for creatinine
U-Na x U-volume / P-Na x time or
-------------------------------------------------
- U-Creat x U-volume / P-Creat x time
U-Na x P-Creatinine or
------------------------------------------
P-Na x U-Creatinine FENa 100 x
FENa
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ACUTE RENAL FAILURE BIOCHEMICAL CHANGES IN PLASMA
Increased Decreased POTASSIUM (K) SODIUM
(Na) HYDROGEN ION (H) BICARBONATE
(HCO3-) PHOSPHATE (PO42-) CALCIUM
(Ca2) UREA CREATININE (Cr) MAGNESIUM
(Mg2) URATE
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PLASMA BIOCHEMICAL CHANGES IN PROGRESSIVE RENAL
FAILURE
GFR (mL/min) Analyte Increased 60 120 Nil 30
60 Creatinine Urea 20 30 K, H, (? HCO3-) 10
20 Urate PO42-
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• Clinical Example
• A 71-year-old man presented with dizziness and
• melaena from a bleeding peptic ulcer.
• Plasma Reference range
• Na 140 mmol/L 135 - 145
• K 5.1 mmol/L 3.5 - 4.8
• Urea 23.9 mmol/L 3.0 - 8.0
• Creatinine 156 umol/L 60 - 120
• HCO3- 19 mmol/L 22 - 32
• Urine
• Na 17 mmol/L
• Creatinine 9350 umol/L 10000 - 20000
• Osmolality 785 mmol/kg 50 - 1200

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Clinical Example
P-Urea / Creatinine ratio 153 Urine
Osmolality 785 U / P-Creatinine ratio
60 FENa 0.23
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Clinical Example
Diagnosis Mild pre-renal azotaemia due to acute
blood loss.
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PROTEINUIRA (1)

• Filtration through the glomerular membrane is
  dependent on molecular size with a cutoff between
  20 - 40 A, corresponding to a protein molecular
  mass about 30 - 70 kDa
• Negatively charged molecules have lower
  permeability
• Small proteins like ?2-microglobulin (13.5 kDa)
  and Lyzozyme (11.5 kDa) are freely filtered but
  they are almost completely reabsorbed in the
  proximal tubules
• Normal daily excretion lt 150 mg about 40 - 50
  is Albumin (67 kDa)

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PROTEINURIA (2)
Measurement of Urine Protein

• Specimen
• Timed collection 24-hour, 12-hour overnight,
  4-hour
• Urine Protein / Creatinine ratio with random
  sample

• Dipstick methods for Urine Protein
• Most sensitive to albumin
• Poor method for detecting tubular proteinuria

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PROTEINURIA Classification

• 1. Overload Proteinuria
• Bence Jones (multiple myeloma)
• Myoglobin (crush injury, rhabdomylosis)
• Haemoglobin

• 2. Tubular Proteinuria
• Mostly low MW proteins (not albumin)
• e.g., Fanconis, Wilson, pyelonephritis,
  cystinosis, heavy metal toxicity (Cd, Pb, Hg),
  galactosaemia

• 3. Glomerular Proteinuria
• Mostly albumin at first, but larger proteins
  appear as glomerular membrane selectivity is lost
  as disease progresses

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Other Causes of Proteinuria

• Orthostatic proteinuria Protein excretion varies
  with posture, increasing on standing. Orthostatic
  proteinuria present in about 10 - 20 healthy
  subjects at prolonged upright posture remits if
  the subject remains recumbent
• Transient Proteinuria Mild to moderate
  proteinuria may be found in systemic illnesses
  apparently not related to the kidneys, e.g., high
  fever, congestive heart failure, and seizures.
  Transient proteinuria may also be found in
  healthy athletes after strenuous exercise and
  often in urinary tract infection.

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Nephrotic Syndrome
Proteinuria gt 3.5 gm/day/1.73 m2 Associated with
hypoalbuminaemia, hyperlipoproteinaemia and
oedema. Where protein loss is relatively
selective for small molecules, larger proteins
such as ?2-macroglobulin are increased in the
plasma Glomerular diseases due to e.g., diabetes,
systemic lupus erythematosis, glomerulonephritis
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RENAL CALCULI (1)
Investigation of patients with renal calculus
formation is of value because the majority of
these patients will have further episodes of
stone formation, which is often the final common
path for several disorders Biochemical analysis
of renal calculi is thus important in detecting
the underlying causes of stone formation
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RENAL CALCULI (2)

• Types of Stones
• Calcium phosphate/carbonate may be a consequence
  of primary hyperparathyroidism or renal tubular
  acidosis
• Magnesium, ammonium and phosphate often
  associated with urinary tract infections
• Calcium oxalate commonest, aetiology often
  obscure often associated with idiopathic
  hypercalciuria, intermittent hyperoxaluria, low
  urinary citrate, or rarely primary hyperoxaluria
• Uric acid may be a consequence of hyperuricaemia
• Cystine very rare, associated with cystinuria

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RENAL CALCULI Investigation

• Chemical analysis of the calculus
• Blood biochemical profile looking in particular
  at calcium, phosphate, bicarbonate, creatinine
  and alkaline phosphatase
• Determination of pH and amino acids, microscopy,
  culture on a random early morning urine specimen
• 2 or more 24-hour urine collected while patients
  are on their usual diet, looking at volume,
  creatinine, calcium, phosphate, oxalate, urate
  and citrate
• PTH level and acid loading test for selected
  patients (e.g., suspected primary
  hyperparathyroidism, RTA)

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Prostate Specific Antigen (PSA) - (1)

• Approved by FDA as a tumour marker for carcinoma
  of prostate
• A protease
• Localised to prostatic ductal cells
• Barely detectable in female
• Liquefies coagulum of seminal fluid
• Enzymatically active PSA forms stable complexes
  in blood with antichymotrypsin (PSA-ACT) and
  ?2-macroglobulin (PSA-A2M)
• Enzymatically inactive PSA remains as free form
  (fPSA)

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Prostate Specific Antigen (PSA) - (2)

• Free PSA (fPSA)
• 30 kDa, 10 - 40 of total in plasma
• of fPSA decreases in patients with CA prostate
  as total PSA level increases

• Total PSA
• Upper cutoff usually taken at 4 ng/mL
• Probability of carcinoma generally parallel the
  blood levels
• Probability of carcinoma increases further with
  lower Free / Total PSA ratio
• Total PSA serial measurement is adequate for
  monitoring of disease progression / recurrence
  after treatment

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Thank You!
Dr. Sidney Tam