Transcript No Slide Title

UROGENITAL SYSTEM
Biochemical Investigations of
Urogenital Diseases
MBBS Year-2 Lecture
26 September 2002
8:30 - 9:30 am
Dr. Sidney Tam
Hon Clinical Professor
Department of Pathology
The University of Hong Kong
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
Renal Blood Flow (RBF)
1200 mL/min
~ 20% Cardiac Output
Glomerular Filtrate Rate
18 L/day
125 mL/min (Filtration Fraction ~ 10%)
Urine Formation
~ 1.5 L/day
1 mL/min
~ 99% H2O in glomerular ultrafiltrate reabsorbed by the kidney
~ 65% occurs in the proximal renal tubules accompanied by Na+ and
Cl- reabsorption
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. < 400 mL
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
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
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.
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
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:
Body Weight:
Plasma Creatinine conc:
Year
Kg
mmol / L
Correlates with measured values of GFR provided that:
i.
ii.
iii.
Plasma [creatinine] is not within normal range
Renal impairment is not severe
No inhibition of tubular secretion of creatinine by medications
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
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
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]
Conditions Affecting [UREA]
Independent of GFR
 UREA
 UREA
* High Protein Diet
* Liver Disease
* Gastrointestinal Bleeding
* Malnutrition
* Tissue Trauma
* Glucocorticoids
* Tetracycline
Conditions Affecting [CREATININE]
Independent of GFR
Condition
Mechanism
Spurious or True Elevation:
*
*
*
*
Ketoacidosis
Cefoxitin, Cephalothin
Ingested cooked meat
Drugs (aspirin, cimetidine
Non creatinine chromogen
Non creatinine chromogen
Gastrointestinal absorption of creatinine
Inhibition of tubular creatinine secretion
trimethoprim, amiloride
triamterene, spironolactone)
Decrease:
* Increasing age
* Cachexia
Physiological  in muscle mass
Pathological  in muscle mass
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
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)
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 > 600 mmol/kg or > 2 x concomitant
plasma Osmolality practically excludes the diagnosis
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 > 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
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
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.
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
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.
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
Differentiation between PRA and ATN
Laboratory Test
Pre-Renal
Azotaemia
Acute Tubular
Necrosis
P- Urea / Creatinine ratio
> 60
Ur Sodium (mmol/L)
< 20
Ur Osmolality (mmol/kg)
> 500
Ur / P Creatinine ratio
> 40
Fractional excretion of
< 1%
filtered Sodium % (%FENa)
< 40
> 40
< 350
< 20
> 2%
Urine Sediment
Brown
granular
casts, cellular
debris
Normal or
occasional
granular casts
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
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 ]
or
U-Na x P-Creatinine
-----------------------------------------P-Na x U-Creatinine
% FENa = 100% x FENa
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
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-
Clinical Example
A 71-year-old man presented with dizziness and
melaena from a bleeding peptic ulcer.
Plasma :
Na+
K+
Urea
Creatinine
HCO3-
Reference range
140
5.1
23.9
156
19
mmol/L
mmol/L
mmol/L
umol/L
mmol/L
135 - 145
3.5 - 4.8
3.0 - 8.0
60 - 120
22 - 32
Urine :
Na+
Creatinine
Osmolality
17
mmol/L
9350 umol/L
785 mmol/kg
10000 - 20000
50 - 1200
Clinical Example
P-Urea / Creatinine ratio
= 153
Urine Osmolality
= 785
U / P-Creatinine ratio
= 60
% FENa
= 0.23
Clinical Example
Diagnosis:
Mild pre-renal azotaemia due to
acute blood loss.
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 < 150 mg; about 40 - 50% is
Albumin (67 kDa)
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
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., Fanconi’s, 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
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.
Nephrotic Syndrome
Proteinuria > 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
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
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
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)
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 2macroglobulin (PSA-A2M)
• Enzymatically inactive PSA remains as free form (fPSA)
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
Thank
You!
Dr. Sidney Tam