Kidney Function Tests Flashcards
Tests for GFR
Clearance:
-Inulin clearance
-Creatinine clearance
-Urea clearance
Phenolsulfonphthalein dye test
GFR
Cystatin C
GFR
Tests for Renal Blood Flow
BUN
Creatinine
Uric acid
Tests Measuring Tubular Function
Excretion:
Concentration:
-Para-amino hippurate test (Diodrast test)
-Phenolsulfonphthalein dye test
-Specific gravity
-Osmolality
Decreases by 1.0 mL/min/year after age 20-30 years
GFR
of glomerular filtrate is produced daily
150 L
Reference method for GFR
Inulin clearance
Best alternative method
Creatinine clearance
Measure of the completeness of a 24-hour urine collection
Creatinine clearance
Creatinine clearance Excretion:
1.2-1.5 g creatinine/day
Demonstrate progression of renal disease or response to therapy
Urea clearance
Low MW protease inhibitor
Cystatin C
Filtered > Not secreted > Completely reabsorbed (PCT)
Cystatin C
Indirect estimates of GFR
Cystatin C
Its presence in urine denotes damage to PCT
Cystatin C
Synthesized from Ornithine or Kreb’s Henseleit cycle
BUN
First metabolite to elevate in kidney diseases
BUN
Better indicator of nitrogen intake and state of hydration
BUN
BUN > Urea (mg/dL)
2.14
Inhibit urease
Fluoride or citrate
Enhance color development (BUN mtd)
Thiosemicarbazide
Ferric ions
Yellow diazine derivative
Diacetyl monoxime method
BUN: Routinely used
Urease method
: prepared from jack beans
Urease
Urea —(Urease)–>
NH4 + Berthelot reagent (Measure ammonia)
Coupled urease
Glutamate dehydrogenase method
UV enzymatic method
Coupled urease
BUN: Reference method
Isotope dilution mass spectrometry
For research purposes
Isotope dilution mass spectrometry
NPN
45% Urea
20% Amino acid
20% Uric acid
5% Creatinine
1-2% Creatine
0.2% Ammonia
Creatinine: Derived from
alpha-methyl guanidoacetic acid
Produced by 3 amino acids (methionine, arginine, lysine)
Creatinine
Most commonly used to monitor renal function
Creatinine
Enzymatic methods (Creatinine)
Creatinine Aminohydrolase – CK method
Creatinase-Hydrogen Peroxide method – benzoquinonemine dye (red)
Creatininase (a.k.a. creatinine aminohydrolase)
Formation of red tautomer of creatinine picrate
Direct Jaffe method
Interferences (Direct Jaffe) Falsely increased:
Ascorbate
Glucose
Uric acid
Alpha-keto acids
(+) Red orange tautomer
Folin Wu Method
True measure of creatinine
Lloyd’s or Fuller’s Earth method
Sensitive and specific
Lloyd’s or Fuller’s Earth method
Uses adsorbent to remove interferences (UA, Hgb, Bili)
Lloyd’s or Fuller’s Earth method
Lloyd’s reagent
Sodium aluminum silicate
Fuller’s earth reagent
Aluminum magnesium silicate
Jaffe reagent (Alk. picrate)
Satd. picric acid + 10% NaOH
Popular, inexpensive, rapid and easy to perform
Kinetic Jaffe method
Requires automated equipment
Kinetic Jaffe method
Elevated urea and creatinine in blood
Azotemia
Decreased GFR but normal renal function
Pre-renal azotemia
Dehydration, shock, CHF
Pre-renal azotemia
Increased: BUN
Normal: Creatinine
Pre-renal azotemia
True renal disease
Renal azotemia
GFR Striking BUN level but slowly rising creatinine value
Renal azotemia
BUN = >100 mg/dL
Creatinine = >20 mg/dL
Uric acid = >12 mg/dL
Renal azotemia
Urinary tract obstruction
Post renal azotemia
Decreased GFR
Pre and Post renal azotemia
Nephrolithiasis, cancer or tumors of GUT
Post renal azotemia
Creatinine = normal or slightly increased
Post renal azotemia
Marked elevation of urea, accompanied by acidemia and electrolyte imbalance
Uremia
(K+ elevation) of renal failure
Uremia
Normocytic, normochromic anemia
Uremia
Uremic frost (dirty skin)
Uremia
Edema
Uremia
Foul breath
Uremia
Urine-like sweat
Uremia
From purine (adenine and guanine) catabolism
Uric acid
Uric acid Excretion:
1g/day
-Gout
Hyperuricemia
-Increased nuclear metabolism
Hyperuricemia
-Chronic renal disease
Hyperuricemia
-Lesch-Nyhan syndrome (HGPRT deficiency)
Hyperuricemia
Fanconi’s syndrome
Hypouricemia
Wilson’s disease
Hypouricemia
Hodgkin’s disease
Hypouricemia
Stable for 3 days
Methods (Uric acid)
Potassium oxalate cannot be used
Methods (Uric acid)
Methods (Uric acid) Major interferences:
Ascorbate and bilirubin
Phosphotungstic acid mtd:
Uric acid + Phosphotungstic acid —(NaCN/NaCO3)–> Tungsten blue + Allantoin
NaCN
Folin
Newton
Brown
Benedict
NaCO3
Archibald
Henry
Caraway
Incubation period after the addition of an alkali to inactivate non-uric acid reactants
Lagphase
UREA: Simplest and most specific method
Uricase method
URIC ACID: Candidate reference method
Uricase method
Uricase method
Uric acid (Absorbance at 293nm) —[Uricase]–> Allantoin (No absorbance)
Decrease in absorbance α uric acid concentration
Uricase method
Measures renal plasma flow
Para-amino hippurate test
Reference method for tubular function
Para-amino hippurate test
Measures excretion of dye proportional to renal tubular mass
Phenolsulfonphthalein dye test
6 mg of PSP is administered IV
Phenolsulfonphthalein dye test
Collecting tubules and loops of Henle
Concentration tests
Concentration tests Specimen:
1st morning urine
Specific gravity
Affected by [?]
SG > [?]: X-ray dye and mannitol
[?]= SG of ultrafiltrate in Bowman’s space
solute number and mass
1.050
1.010
Total number solute particles present/kg of solvent (moles/kg solvent)
Osmolality
Affectted only by number of solutes present
Osmolality
Urine osmolality = due to
Serum osmolality = due to
urea
sodium and chloride
Det. by Colligative properties:
Freezing point
Vapor pressure
Osmotic pressure
Boiling point
Freezing point (incr. osm. = decr. FP)
Vapor pressure (incr. osm. = decr. VP)
Osmotic pressure (incr. osm. = incr. OP)
Boiling point (incr. osm. = incr. BP)
Direct methods (Osmolality)
= popular method
(Seebeck effect)
Freezing point osmometry
Vapor pressure osmometry
Incr. vasopressin (H2O reabsorption) =
decr. plasma osmolality
Tubular failure
Increased:
Decreased:
BUN, creatinine, calcium
Phosphate
Difference between measured and calculated osmolality
Osmolal gap
Sensitive indicator of alcohol or drug overdose
Osmolal gap
Sensitive indicator of alcohol or drug overdose
Osmolal gap
Osmolal gap: >12 mOsm/kg
DKA
Drug overdose
Renal failure
Creatinine Clearance:
Male =
Female =
85-125 mL/min
75-112 mL/min
BUN =
8-23 mg/dL
BUN =
8-23 mg/dL
Uric acid:
Male =
Female =
3.5-7.2 mg/dL
2.6-6.0 mg/dL
Renal plasma flow (PAH) =
600-700 mL/min
Renal blood flow (PSP) =
1200 mL/min
SG =
1.005-1.030
Osmolality:
Serum =
Urine (24-hr) =
275-295 mOsm/kg
300-900 mOsm/kg [<290 mOsm/kg = kidney damage]
Urine osmolality: Serum osmolality =
1:1 to 3:1
[= Glomerular disease]
> 1:1
[= loss of renal concentrating ability]
1.2:1
[= Diabetes Insipidus]
<1:1
-Increased nuclear metabolism Tx:
Allopurinol