AUBF 19: RENAL FUNCTION TESTS

Clearance test

Test for glomerular function

Titratable acidity

Test for proximal & distal tubular function; ability to secrete/ reabsorb H+ ions

Osmolarity

Test for loop of Henle function; concentrating and diluting ability of the kidney

Ammonia

Test for Ddistal convoluted tubular function

Free water clearance

Test for collecting duct function; % of H2O in pee

glomerular filtration rate renal plasma flow reabsorption & excretion

various aspects of renal function (3)

creatinine clearance

In clinical practice, determination of _____ is a measure of GFR

water deprivation; vasopressin administration

In clinical practice, _____ & _____ tests to determine urinary concentrating/diluting ablity

NaHCO3 & NH4Cl loading test

In clinical practice, _____ to examine urinary acidification are usually sufficient for dxostic evaluation and measurement of kidney fxn

T

T/F grading of chronic renal insufficiency and dosage of drugs are excreted primarily in the urine based on GFR

Clearance tests

glomerular filtration test

clearance tests

standard test to measure filtering capacity of the glomeruli

clearance tests

measures that rate at w/c the kidneys are able to remove the filterable substance from the blood

=GFR

some substances when filtered enter the tubules are ot reabsorbed ans so 100% excreted

clearance > GFR

some substances are filtered, enter the tubules adn more of the substances is secreted enters the tubules by excretion

cystatin C

some substances are filtered, enter the tubules but are completely reabsorbed, so they did not reach the final urine

urea cystatin C inulin radionuclides B2 microglubulin creatinine

substances used for clearance tests (6)

urea

measured by earliest glomerular filtration tests bec of its presence in all urine specimens

F; 60-40

T/F 60% of filtered urea is reabsorbed

F; excretion-reabsorption

T/F normal values fo urea were adjusted to reflect excretion

F; 20-2

T/F px were hydrated to produce urine flow of 20 ml/min to ensure that no more that 40% urea was reabsorbed

creatinine radionuclides inulin B2 microglobulin

replaced urea as substance used for clearance test (4)

cystatin c

LMW nonglycosylated CHON produced at a constant rate by all nucleated cells of the body

F; totally

T/F cystatin C is freely filtered by the glomeruli, totally secreted and not reabsorbed by the renal tubules; little or no cystatin is excreted in the urine

1 mg/L

normal adult circulating level of cystatin C

cystatin C

better indicator of renal function compared to crea in early stages fo GFR impairment as it is independent of age, gender, body composition and muscle mass

enzyme immunoassays immuno-turbidometry

expensive & kit-based techniques used to estimate cystatin C in blood (2)

inulin

polymer of fructose, an extremely stable substance that is not reabsorbed or secreted by the tubules

inulin

must be infused at a constant rate throughout the testing period (exogenous procedure) thus not routinely used for GFR

radionuclides

injection not only determines GFR through plasma disappearance of the material but also enable visualization of the filtration in one or both kidneys

B2 microglobulin

plasma levels with good correlation with glomerular filtration rate

human leukocyte antigens

B2 microgobulin dissociate from _____ at a constant rate and is rapidly removed from the plasma by glomerular filtration

RIA EIA

used for measurement of B2 microglobulin

F; increase-decrease

T/F rise of B2 microglobulin in plasma is a more sensitive indicator of an increase in GFR than crea clearance

immunologic disorders of malignancy

B2 microglobulin is not reliable in px who have a history of _____ bec of the many WBCs

creatinine

currently employed as the test substance for clearance tests

creatinine

provides the lab with an endogenous procedure for evaluating glomerular fxn

creatine; phosphocreatine

creatinine is derived form the metabolism of ____ and ____, the bulk of w/c is in the muscle

T

T/F disadvantage of crea not found w/ inulin: some crea is secreted by the tubules, and secretion increases as blood levesl rise

chromogen

disadvantage of crea not found w/ inulin: _____ present in human plasma react in chemical analysis but their presence may hep counteract the falsely elevated rates caused by tubular secretion

F; -20C-room temp

T/F disadvantage of crea not found w/ inulin: urinary crea will be broken down by bacteria if specimens are kept at -20C for extended periods of time

4C

temp 24-hr urine specimen for crea is kept at

heavy meat

disadvantage of crea not found w/ inulin: _____ diet during collection of 24-hr urine specimen will influence the creatinine results

muscle-wasting dss

disadvantage of crea not found w/ inulin: crea clearance is not a reliable indicator in px suffering from _____

F; confirm-screen

T/F crea clearance is used to confirm GFR

use of improperly timed urine specimens

greatest source of error in any clearance test

nephrons

significance of crea clearance: # of fxning & fxnal capacity of _____

T

T/F though 1/2 of nephrons become nonfunctional, change in GFR will not occur if the remaining nephrons double their filtering capacity

early

significance of crea clearance value doesn't lie in the detection of _____ renal dss

crea clearance tests

used to determine the extent of nephron damage in known cases of renal dss

crea clearance tests

monitor the effectiveness of tx designed to prevent further nephron damage

crea clearance tests

determine feasability of administering meds w/c can build up toxic levels if GFR is markedly reduced

Cockcroft & Gault

frequently used formula or predicting the crea clearance from the serum creatinine

age sex weight

included in Cockcroft & Gault

tubular reabsorption

loss of _____ is often the first fxn affected in renal dss

concentration tests

tubular reabsorption tests

concentration tests

tests to determine the ability of tubules to reabsorb essential salts & H2O that have been nonselectively filtered by the glomerulus

1.010; concentrated

in concentration tests, ultrafiltrate that enters the tubules have an spgr of ____ thus after reabsorption the final urine product is expected to be more _____

T

T/F clinically, many specimens dont have a spgr higher that 1.010 but there is no renal dss present

hydration

urine conc is largely determined by the body's state of ____

T/F normal will reabsorb only the amount of water necessary to preserve an adequate supply of body water

fishberg test mosenthal test

water deprivation tests (2)

fishberg method

pxs deprive fluids for 24 hrs prior to measuring spgr

mosenthal test

compare volume and spgr of day & night urine samples to evaluate concentrating ability

osmometry; neonates

quantitative measurement of renal concentrating ability is best assessed thru the use fo _____ (essentially in ____)

1.025; 16

normal concentrating ability should have a spgr of ____ when depreived of fluids for ____ hours

specific gravity

depends on the the # of particles present in a solution and density of these particles

osmolarity

affected only by # of particle present

23; 35.5; 60

substances of interest are small molecules primarily Na (MW _____) & Cl (MW _____) urea (MW ____) contribute to the spgr

osmole

1g MW of substance divided by # of particle into w/c it dissociates

glucose; NaCl

a non ionizing susbtance like _____ (MW 180) has 18 g per osole while _____ (MW 58.5) if completely dissociated contains 29.25 g per osmole

colligative property

osmolarity of a solution can be determined by measuring a property that is mathematically related to the # in the solution (_____) and comparing this value with the value obtained from the pure solvent

lower freeing point higher boiling point increased osmotic pressure lower vapor pressure

solute dissolved in solvent causes the ff changes in colligative properties (4)

freezing point depression vapor pressure osmometer

clinical osmometers (2)

freezing point depression

first principle used in osmometry

freezing point depression; -17C

determine the freezing point of a sol'n by supercooling a measured amount of sample by approximately _____

vapor pressure osmometer

actual measurement performed is the dew point

dew point

temp at which water vapor condenses into a liquid

microsamples; evaporation

vapor pressure osmometer uses _____ (<0.01) thus _____ of the sample must be prevented

Nacl; partially

clinical osmometer uses _____ as reference standards bec a sol'n of _____ ionized substances is more representative of urine & plasma conc

lipemic serum lactic acid or volatile susbstances

factors that influence on true osmolarity readings (2)

F; only-and freezing point osmometers

T/F displacement of serum water by insoluble lipids produces false results with vapor pressure only

20 mins

false high results occur w/ both methods if serum samples are not separated or refrigerated w/in ____thus causing acidic urine

-initial evaluation of renal concentrating ability -monitor course of renal dss -monitor fluid & electrolyte therapy -diff dx of hypernatremia, hyponatremia, polyuria -evaluate secretion of & renal response to ADH

major clinical uses of osmolarity (5)

275-300 mOsm

normal serum osmolarity

50-1400 mOsm; serum; urine

normal values for urine Osm is hard to establish and values can range between _____ so it is necessary to measure both _____ & _____ Osm and to evaluate ratio from 2 readings

1:1; 3:1

urine to serum ratio: random is at least _____, after controlled fluid intake _____

-if DI is due to dec ADH production or inability of renal tubules to respond to ADH -tumors that produce ADH-like substances -know cause fo renal pathology

urine to serum osmolarity ratio in conjunction with controlled fluid intake and injection of ADH (3)

renal defect in concentrating ability; defect in production

failure to injected ADH indicates a _____ while a response to ADH is assoc w/ a _____

free water clearance

calculated when dealing w/ difficult dxostic probs

timed urine

expand the urine to seurm osmolarity ration by performing the analyses using a _____ specimen & calculating the free water clearance

osmolar clearance; standard clearance; osmolar clearance; urine volume

free water clearance is determined by calculating the _____ first using the _____ formula and substract _____ value from the _____

dehydration; conservation of water

less than necessary amount fo water is being excreted indicating a possible state of _____ & _____

renal concentration/dilution

if the value is 0, no _____ would be taking place

decreased

if the value is +1.43, ADH production would be _____

free water clearance

used to determine ability of kidneys to respond to state of hydration

-impaired tubular secretory ability -inadequate presentation of susbtace to the capillaries due to dec renal blood flow

abnormal result of tubular secretion and RBF test is caused by either (2)

p-aminohippuric acid (PAH) test

most common test for tubular secretion and RBF test

excretion of phenolsulfonphthalein (PSP)

used to evaluate tubular secretion and RBF test

-interference of meds & inc. waste products in px serum -need to obtain several very accurately timed urine specimen

stdization & interpretation of PSP results is hard due to (2)