Kidney function test Flashcards
References: Book ni Dean Rodriguez sa CC Trans ni Rovie Vila
It is paired, bean-shaped organs located retroperitoneally on either side of the spinal column
Kidney
Outer region of the kidney
Cortex
Inner region of the kidney
medulla
functional and structural unit of the kidney
Nephron
What are the 5 basic parts of the nephron
- Renal Corpuscle (Glomerulus)
- Loop of Henle
- Proximal Convoluted Tubule (PCT)
- Distal Convoluted Tubule (DCT)
- Collecting Duct
Filtering unit or part of the kidney, retaining large proteins and protein-bound constituents while most other plasma should be approximately equal to ECF without protein
Renal Corpuscle (Glomerulus)
Cells in Bowman’s capsule in the kidneys
podocytes
Expanded end of a renal tubule
Bowman’s capsule
composed of the thin descending limb, which spans the medulla, and the ascending limb, which is located in both the medulla and the cortex
- highest osmolarity in the nephron
- enables water reabsorption to be increased or decreased in response to body fluid changes in osmolality
loop of Henle
all parts of kidney are permeable except
ascending loop
Glomerular filtrate =
1.000 - 1.010 (Isosthenuric)
It is responsible for the reabsorption of Sodium, Amino acids, Glucose, Urea, Water (SAGUW)
Proximal Convoluted Tubule (PCT)
Site of secretion
Distal Convoluted Tubule (DCT)
- collect the urine that drains from each nephron
- final site for either concentrating or diluting urine
Collecting Duct
A measure of the clearance of normal molecules that are not bound to protein and are freely filtered by the glomeruli neither reabsorbed nor secreted by the tubules
Glomerular filtration rate
GFR decreases by ____ mL/min/year after age 20-30 years
1.0 mL/min/yea
How much glomerular filtrate is produced daily?
150 L (according to the book of Dean rodriguez CC)
Removal of substance from plasma into urine over a fixed time
Clearances
Plasma concentration and clearance is _____ proportional
Inversely
Formula for Clearance
= U/P x Volume/minutes x 1.73/A
U = conc. of urine
P = Conc. of plasma
V = Volume of urine for 24 hours
Minutes = Time required to collect urine (1440 mins)
1.73 = Ave. body surface
A = Body surface area of the patient
Preservative for Urinary hormones
Hydrochloric acid
Preservative for 24 hr urine sample
refrigeration/cooler
- most commonly used; you don’t need additional preparation for the patient (no injections or fasting); collection should be a 24-hr. urine sample
- Production and excretion is related directly to muscle mass
Clearance test
How many creatinine is excreted per day?
1.2-1.5 g
Continuous infusion for inulin clearance
500 mL of 1.5% inulin soln.
Priming dose for Inulin clearance
25 mL of 10% inulin solution
Gold standard/reference method of clearance
Has a higher values in male due to larger renal mass
Inulin clearance
Reference values of inulin clearance?
127 mL/min - Male
118 mL/min - Female
Why creatinine clearance is excellent for measurement of renal function?
Creatinine is freely filtered by the glomeruli but not reabsorbed
Production and excretion is related directly to muscle mass
Creatinine clearance
Causes of increased creatinine clearance
1) High cardiac output
2) Pregnancy
3) Burns
4) Carbon monoxide poisoning
CHUBPI
Causes of decreased creatinine clearance
1) Impaired kidney function
2) Shock, dehydration
3) Hemorrhage
4) Congestive heart failure
CHIS
Reference values of creatinine clearance?
85-125 mL/min - Male
75-112 mL/min - female
Cockcroft-gault formula
CrCl(mL/min) 140-age x lean body weight(kg)/Serum creatinine (mg/dL) x 72 (x 0.85 if female)
Why the renal clearance of Cystatin C cannot be measured?
Because it is completely reabsorbed
- low-molecular-weight protein produced at a constant rate by most body tissues
- rise more quickly than creatinine levels in acute kidney injury (AKI).
- reabsorbed by the PCT
- Increases more rapidly than creatinine in the early stages of GFR impairement
- Not affected by muscle mass, age, diet and gender
Cystatin C
Reference values of Cystatin C
0.5-1 (adults)
0.9-3.4 (>65 yrs old)
byproduct of protein metabolism
Non-Protein Nitrogenous Compounds (NPN)
- Major end product of protein and amino acid catabolism
- Non-protein nitrogenous compound; 45% total NPN
- 1st metabolite to elevate in kidney diseases
- Better indicator of nitrogen intake and the state of hydration
Blood Urea Nitrogen (BUN)
Conversion factor of BUN to creatinine:
2.40
BUN to Creatinine normal ratio =
10:1-20:1
reference values of BUN
8-23 mg/dL (2.9-8.2 mmol/L)
end product of Diacetyl Monoxime Method
Yellow
Urease Method derived from
jack beans
Sodium Fluoride inhibits Urease.(True/False)
true
UV enzymatic method
Coupled Urease/ Glutamate Dehydrogenase Method:
- Reference method for BUN/Urea
- Definive method for creatinine
Isotope Dilution Mass Spectrometry (IDSM)
- Mother compound
- product of kreb cycle
- First analyte to be elevated in kidney disease
Urea
Causes of decreased BUN
1) Poor nutrition
2) Hepatic disease
3) Impaired absorption (celiac disease)
4) Pregnancy
Causes of increased BUN
1) Chronic renal disease
2) Stress
3) Burns
4) High protein diet
5) Dehydration
- Product of muscle breakdown
- most common analyte to be used in monitoring kidney disease
Creatinine
Creatinine is produced by 3 amino acids such as:
1) Methionine
2) Arginine
3) Lysine
Reference value for Creatinine
0.5-1.5 mg/dL (44-133 umol/L)
Common method used for creatinine
Jaffe method
2 reagents used in Jaffe method
Jaffe A: saturated picric acid (yellow)
Jaffe B: 10% sodium hydroxide
Jaffe A + Jaffe B=
Alkaline picrate solution
End color of Jaffe method
red-orange complex (red tautomer)
- Sensitive and specific method
- Time consuming and not readily automated
- not routinely performed
Modified Jaffe method
Reagents used in modified jaffe method to remove interferences
- Lloyd’s reagent: Sodium aluminum silicate
- Fuller’s earth: Aluminum magnesium silicate
- Has potential to replace Jaffe method (specific than Jaffe method)
- Without interference from acetoacetate or cephalosporins
- Creatininase is also known as creatinine aminohydrolase
Creatininase Hydrogen Peroxide (H2O2) method
- Enzymatic method that requires large of pre-incubation
- not widely
Creatinine Aminohydrolase - CK method
Used to eliminate nonspecificity of the Jaffe rxn; Specific than Jaffe test
Enzymatic method
- Method that is popular, inexpensive, rapid and easy to perform
- It requires automated equipment for precision
- Allows a rate-dependent separation of creatinine from interfering substances
Kinetic jaffe method
Interferences in Kinetic Jaffe method
alpha-Keto acids and cephalosporins
Causes of increased creatinine
1) Impaired renal function
2) Chronic nephritis
3) Muscular diseases - Myasthenia gravis, Muscular dystrohpy
4) Congestive heart failure
Causes of decreased creatinine
1) Decreased muscle mass
2) Advanced and severe liver disease
3) Pregnancy
4) Inadequate dietary protein
- clinical term of azotemia
- elevated BUN and Creatinine with signs and symptoms
- Kidneys fail to eliminate waste products of metabolism
- Characterized by anemia (normocytic, normochromic), Uremic frost (Dirty skin), generalized edema, foul breath and sweat is urine-like.
- Symptoms: itch, restlessness syndrome (kumukuyakoy), anxiety, insomnia
Uremia
- Increased levels of BUN and Creatinine
Azotemia
- problem lies before kidney
- marked decrease in renal blood flow
- most common cause = hypoperfusion
Pre-Renal
Why renal blood flow in pre renal azotemia decreases?
GFR decreases and Tubular reabsorption increases leading to slower filtrate flow
Causes of Pre-renal azotemia
- Dehydration
- Shock
- Congestive heart failure
- Hypoperfusion
The result of BUN and Creatinine of an individual who has hypoperfusion
BUN = increased
Crea = normal
Pre-renal azotemia BUN to crea ratio =
> 20:1
- problem lies within the kidney
- damage to structures within the kidney
Renal Azotemia
What is the level of BUN and Crea in Renal Azotemia
both BUN and Crea levels are elevated
BUN = >100 mg/dL
Creatinine = >20 mg/dL
Uric acid = >12 mg/dL
Renal azotemia BUN to crea ratio =
10-20:1
Causes of renal azotemia
- Acute/chronic renal disease
- glomerulonephritis
- Tissue damage
- Decreased GFR
- Striking BUN level but slowly rising creatinine value
- problem lies after the kidney
- obstruction of urine outflow from the kidney
- Urea level is higher than creatinine
Post-renal azotemia
Why the level of urea is higher than creatinine in Post renal azotemia?
- due to back-diffusion of urea into circulation
- increased urea and creatinine in blood
causes of post renal azotemia
- renal calculi (nephrolithiasis)
- cancer or tumors of genitourinary tract
- Prostate enlargement
- Obstruction
Post renal azotemia BUN to Crea ratio =
<10:1
most common cause of kidney failure In the Philippines
- diabetes
- hypertension
Most common cause of UTI
- Escherichia coli (females)
- S. saprophyticus (sexually active females)
- Sexually transmitted (males)
Causes of low ratio (BUN:Crea) <10:1
1) Low protein diet
2) Acute tubular necrosis
3) Repeated dialysis
4) Hepatic disease
Causes of high ratio (BUN:Crea) >20:1 with normal creatinine
1) Prerenal azotemia
2) Dehydration
3) Catabolic states
4) GI hemorrhage
5) High protein diet
Causes of high ratio (BUN:Crea) >20:1 with increased creatinine
1) Postrenal azotemia
2) Pre renal azotemia with renal disease
3) Renal failure
- product of purine metabolism (purine and pyrimidine which are the two categories of the bases of DNA)
- Final breakdown of nucleic acids catabolism in humans
- Filtered, partially reabsorbed and secreted in the renal tubules
Blood Uric acid
BUA is formed from _____ by the action of ____ in the liver and intestine
Xanthine, Xanthine oxidase
BUA is derived from 3 sources:
1) Catabolism of ingested nucleoproteins
2) Catabolism of endogenous nucleoproteins
3) Transformation of endogenous purine nucleotides
Reference values of BUA
Uricase
- 3.5-7.2 mgdL (0.21-0.43 mmol/L) - male
- 2.6-6.0 mg/dL (0.16-0.36 mmol/L) - female
Foods that increase or with high uric acid
- beans (mungo bean)
- Balunbalunan/gizzard
The principle of chemical method used in BUA
Reduction-oxidation rxn
Reagent used in chemical method in BUA
a) Caraway
- most commonly used
- It uses Sodium carbonate (NaO3)
b) Folin
- Uses Sodium Cyanide which is toxic
The incubation period after the addition of an alkali (NaCN/Na2CO3) to inactivate non-uric acid reactants
Lag phase
Enzymatic method used in BUA
Uricase method
- Simpliest and the most specific method used for uric
acid - Simplest and most specific method
- Candidate reference method
Uricase method
UV absorbance peak of uric acid
293 nm
Principle of Uricase method
- The enzyme uricase oxidizes uric acid to form allantoin.
- Uric acid has a maximum peak of absorption of 293 nm.
- The resultant product (allantoin) has no absorption at this wavelength
- The decrease in the absorbance is proportional to the conc. of uric acid present in the sample
- Total number solute particles present/kg of solvent (moles/kg solvent)
- Affected only by number of solutes present
Osmolality
Colligative properties of Osmolality
1) Freezing point (incr. osm. = decr. FP)
2) Vapor pressure (incr. osm. = decr. VP)
FVD
3) Osmotic pressure (incr. osm. = incr. OP)
4) Boiling point (incr. osm. = incr. BP)
BOI
Biomarkers od Kidney injury
- Kidney injury molecule-1 (KIM-1)
- Neutrophil gelatinase associated lipocalin (NGAL)
- Insulin-like GF binding protein 7 (IGFB7)
- Tissue inhibitor metalloroteinase-2 (TIMP-2)
expressed in proximal tubular cells injured by ischemia or nephrotoxins
Kidney injury molecule-1 (KIM-1)
- a.k.a. lipocalin-2 or siderocalin
- inflammation of kidney parenchyma and in kidney injury
Neutrophil gelatinase associated lipocalin (NGAL)
- deficiency of Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
- increased uric acid
- common in children (orange sand in diapers)
Lesch-Nyhan Syndrome
An important enzyme in the biosynthesis of purines.
- Lack of this enzyme prevents the reutilization of purine bases in the nucleotide salvage pathway
- results in increased de novo synthesis of purine nucleotides and high plasma and urine concentrations of uric acid
Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
Tests measuring tubular function
A) Excretion tests
B) Concentration test
What are the Excretion Tests?
- Para amino hippuric (PAH) acid test
- Phenolsulfonphthalein test
- Measures renal plasma flow
- Reference method for tubular function
Para-amino hippurate test
Ref. range of Para-amino hippurate test
600-700 mL.minute
- Measures excretion of dye proportional to renal tubular mass
- 6 mg of PSP is administered IV
Phenolsulfonphthalein dye test
Ref. range of Phenolsulfonphthalein dye test
1200 mL/minute
- Collecting tubules and loops of Henle
- It detect renal damage that is not yet severe enough to cause elevated plasma urea and creatinine
- Used to assess the quantity of solutes present in urine, which reflects the ability of the kidney to produce a conc. urine
- Monitors the conc. of Cl and Na in urine reveals the ability of the kidney to concentrate the ultrafiltrate in tubules
Concentration test
Specimen used for conc. test
First morning urine
3 most prevalent solutes excreted in concentration test
- Urea
- Cl
- Na
dependent on the number and size of particles
Specific Gravity
dependent on the number of particles; freezing point
Osmolality
