renal function tests Flashcards
influenced by number of SMALL particles in a solution
osmolarity
- Earliest and no longer used
- 40% is reabsorbed results were adjusted for this
- STANDARD METHOD for GFR
- Demonstrate progression of renal disease or response to therapy
- Do not give reliable estimates of GFR
urea clearance test
- Solution properties related to the number of molecules present in the solvent:
- Lower freezing point (laboratory measure)
- Higher boiling point
- Increased osmotic pressure
- Lower vapor pressure (laboratory measure)
- Urine and plasma values are compared with those of pure water
colligative properties
- Polymer of fructose
- No reabsorption or secretion
- Original clearance reference method
- Disadvantage: Requires infusion
- Not routinely used
- Higher values in male due to larger renal mass
inulin clearance test
titrable acidity/urine ammonia
inability to produce an acid urine
renal tubular acidosis
titrable acidity/urine ammonia
first morning, postprandial 2-8 p.m. Lowest pH at night
alkaline tide
test for tubular secretion
- not filtered by the glomerulus but is secreted by the peritubular capillaries
p-amminohippuric acid test
normal creatinine values for:
- men: (?)
- women: (?)
- 107-139 mL/min
- 87-107 mL/min
specimen for titratable acidity/urine ammonia
2-hr urine specimens, fresh or toluene (preservative)
most commonly used substance for clearance test
creatinine
- Test for renal blood flowm (renal plasma flow)
- secreted in proximal convoluted tubule, not by glomerular filtration
- loosely bound to plasma proteins
- completely removed from the blood each time it comes in contact with functional renal tissue
- Exogenous procedure
- Performed in specializing renal laboratories
p-amminohippuric acid (PAH)
high blood; high B2-microglobulin = (?)
renal damage
- Good indicator of early renal disease
- Measure renal concentrating ability
- Often termed concentration tests
- Baseline for determining concentration is the 1.010 specific gravity of the original ultrafiltrate
- Control of fluid intake is necessary for accurate results
tubular reabsorption tests
inulin clearance test
- priming dose: (?)
- continuous infusion: (?)
- reference values: (?)
- 25mL of 10% inulin solution
- 500mL of 1.5% inulin solution
- 127mL/min (male); 118mL/min (female)
inulin clearance test
- exogenous procedure: (?)
- endogenous procedure: (?)
- infusion
- body constituent
- Small protein produced by all nucleated cells; filtered by glomerulus
- Absorbed by the renal tubules and broken down; it is not secreted
- Serum levels directly reflect GFR
- Monitors pediatric patients, diabetics, elderly, and critically ill patients
- Immunoassay procedures available
cystatin c
CCT advantage or disadvantage
- Waste product of muscle destruction found at relatively constant plasma level
- automated chemical tests
advantage
- Exogenous procedure measuring plasma disappearance of an injected isotope
- 125I iothalamate
- Provides simultaneous visualization of the kidneys
radioisotopes
inulin
1st morning urine is included, the result will be?
false increase
osmometry
- Measured sample is supercooled and vibrated to form crystals; heat of fusion raises temperature to freezing point; probe (thermistor) measures freezing point
- lowers freezing point to 1.86 degrees C
- Clinical reference standard is NaCl
freezing point osmometers
- Results are based on functioning nephrons
- Nephrons can double their workload if needed
- This is seen in persons with one kidney
- does not detect early disease
- Monitor extent of known renal disease
- Determine feasibility of administering medications that may build up to toxic blood levels
creatinine clearance test
how many urea is reabsorbed in clearance test?
40%
has same osmolarity as plasma
ultrafiltrate
Tests for tubular secretion of H+ and NH4+
titrable acidity/urine ammonia
- Principle: to determine the amount of creatinine completely removed from the plasma during 1 minute
- Report in milliliters per minute
- This is referred to as the glomerular filtration rate (GFR)
- Greatest error is improperly timed urine specimen
creatinine clearance test
substance used that is a gold standard for clearance test
inulin
patient deprivation of fluid for 24 hours for Specific gravity measurement
fishberg test
creatinine clearance test is affected by what medications?
- gentamycin
- cephalosphorins
- cietidine
comparison of day and night urine in terms of volume and SG
mosenthal test
high blood; low B2-microglobulin = (?)
glomerular damage
- Decreased ADH production
- Inability of tubules to respond to ADH
- After ADH injection
diabetes insipidus (DI)
greatest source of error in creatinine clearance test?
24 hr urine specimen/improperly timed specimen
technical factors in osmometers
- Elevates readings in both instruments
- Separate or refrigerate within 20 minutes
lactic acid
osmometer
- Actual measure is dew point (temperature at which water vapor condenses to a liquid)
- Microsamples on small filter-paper disks in sealed chamber; evaporating sample forms vapor
- Temperature lowered, vapor condenses, thermocoupler measures heat of condensation that raised temperature to dew point.
- Requires careful technique because of microsamples
vapor pressure osmometers
produced as a result of muscle destruction; therefore, normal values are based on size; the larger the person, the more is produced
creatinine
diabetes insipidus
ratio:
- no ADH receptors in CD
- inability to produce ADH
- 1:1
- 3:1
indicates if enough water is excreted to remove wastes and the kidneys response to body hydration
free water clearance
- current routine test substance
- Most commonly used
- SCREENING METHOD of GFR
creatinine clearance test
- Small protein that dissociates from human leukocyte antigens at a constant rate
- Rapidly removed from the plasma by kidneys
- Measured by enzyme immunoassay
- Sensitive indicator of decrease in GFR
- Unreliable in patients with immunological disorders and malignancies
B2-microglobulin
has replaced specific gravity as the test to assess renal concentration function
osmolarity
CCT advantage or disadvantage
- Tubular secretion with high blood levels
- Bacteria break down creatinine if urine is stored at room temperature
- Heavy meat diet during timed collection increases urine creatinine
- Not reliable with muscle-wasting diseases
- Gentamicin, cephalosporins, and cimetidine inhibit tubular secretion
disadvantage
technical factors in osmometers
- Affects both instruments
- Insoluble lipids displace serum water
lipemic serum
substances used for clearance testing
- B2-microglobulin
- cystanin C
- radioisotopes
- urea
- inulin
- creatinine
test for tubular secretion
obsolete because results difficult to interpret
phensulfonphthalein test
the obsolete method in clearance test
urea
used for the quantitative measure of renal concentrating ability
osmometer
technical factors in osmometers
- Elevate results for freezing point osmometers, no effect on vapor pressure instruments
volatile/ethanol
Clinical unit of measure of osmolarity
milliosmole (mOsm)
normal values for osmometry:
- serum: (?)
- urine: (?)
- serum to urine ratio: normal (?); controlled fluid intake (?)
- 275-300 mOsm
- 50-1400 mOsm
- normal (1:1); controlled fluid intake (3:1)
methods not requiring urine collection
- B2-microglobulin
- cystatin c
- radioisotopes
influenced by the number and density of particles in a solution
specific gravity
- Measure rate at which the kidneys can remove a filterable substance from the blood
- Substance cannot be reabsorbed or secreted
- Stability of substance during timed urine collection
- Consistency of plasma level
- Many require accurately timed urine collection
- Availability of tests to measure the substance
clearance test
- Makes use of an exogenous substance, phenolsulfonphthalein dye.
- Standardization and interpretation is difficult to interpret
- Easily interfered with Medication, elevated serum renal analytes.
- Several timed urine specimens requirement
- Possible anaphylactic shock
phenolsulfonphthalein test
frequently used formula
MDRD
- recommended by NKDEP
- used for poeple who has CKD
MDRD-IDMS
what is the result
- if next day 1st morning is not included
false decrease
