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51 Cards in this Set

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-The acceptable range of an analyte or the acceptable result of a lab test for a healthy patient
-diffrentiates b/w sick vs. well
-Established by manufacturer or scientific community
Referenvce range
How do you determine or establish a reference range?
1. Allow volunteers to self identify themselsves as "healthy" and keep a record of sex, age and other relavent parameters.
2.Obtain sample from volunteers(blood,urine,etc.) perform proper lab test
3.Stratify results according to sex and age groups, then look for differences between strata and what the distribution w/i each stratum looks like.
4.For each stratum, determine the central 95th percintile= provisional reference range for that group
95th percentile=
95% of healthy people are in this range
2.5% have higher values
2.5% have lower values
Explain what stratifying the date means
sorting the results into age groups
after you run your tests, dertmine st. dev, and mean, and if all age groups are different, then each group must have seperate reference range.
How do you determine the reference range if you have invented a new test?
minimum n=120, and the analysis must be performed to establish a reference range
After a reference range is established how often must you validate it?
every year, and you only need n=20
When can Parametric statistics be used?
Only when the frequency distribution is Gaussian. When this happens, the reference range= 95%of the group; or mean +/- 2s.d.
How do you calculate percentiles when using non parametric statistics?
Make a list of all the results from the reference range study and order them from low to high. Calculate the 2.5% of n, and the 97.5% of n.
97.5-2.5 give you your 95%
Determine the reference range if 250 results are listed and then give the lower limit and upper limit.
2.5%= 6.25= 6th result
97.5%=243.75 =244th result
LL=43.0
UL=154018.0
Evaluate the use of medical decision points in establishing cut off levels
For most lab tests there is overlap between healthy and diseased populations, this means there are false positives and false negatives.
Evaluate the use of Receiver Operating characteristic (ROC) curves in comparing lab tests.
ROC curves help determine medical decision limits(cut offs) based on sensitivity and specificity.
The ROC plots the FP of the test (x-axis) vs. the TPof the test(y-axis)
IMPORTANT: the point on the curve that falls closest to the upper left corner is the best choice with the highest specificity and sensitivity.
The measurementof intesity of light falling on a surface from a source without consideration of wavelength.
Photometry
Measurement of intensity of light at a selected wavelength
Spectophotometry
what type of measurement technique is most used in clinical chemistry for measuring analytes
spectophotometry
what two principles is spectophotometry based on?
1. substances absorb light at unique wavelentgh
2. the amount of light absorbed is proportional to the amount substance that is present
These principles are based on BEER'S LAW
Light may behave as it does because of discrete energy packets called...
Photons
What is the relationship between wavelength and energy
E=hv
Energy in Ergs=(planks constant(6.62*10^-27)x frequency of light in cycles per second
What is the relationship between of frequency of light and wavelength
Frequency of light is inversely proportional to wavelength. SO
E=hc/(wavelength)
in a visible spectrum, what increases as you go lower on the spectrum, and what increases as you go higher on the spectrum?
As you go lower, you have an increase in energy and go more towards UV rays.
As you go higher, you have an increase in wavelength, and go more towards IR light
Wavelengths <190 nm include...
X rays and Gamma Rays. These photons are able to penetrate through flesh
Wavelengths from 190- 390nm is...
Invisible or ultraviolet light
Wavelengths of 390-750 nm...
visible light
Wavelengths of >750 nm is...
Infrared light
Define absorbance
occurs when electromagnetic radiatin is assimilated by a substance (it is neither reflected nor passed through
Define transmission
occurs when electromagnetic radiation moves through a substance
What happens to the light that is not absorbed by solutions
It is transmitted through the solution
What is the relationship between the color absorbed and the color seen at certain wavelengths?
You see the complimentery color of what color is most obsorbed. ex: Blue is absorbed--> orange is seen
When an atom or molecule absorbs a photon...
Valence electrons are raised from a low energy orbital(ground state) to a higher energy orbital(excited state) by absorbing energy of a photon.
Excited electrons (those in a higher energy orbital) will fall back to ground state by...
emitting energy... aka transmittance
What is the formula for %Transmittance
%T=I/Iox100

I= transmittance
we always assume Io=100, it is incident light
What is Beer's Law?
Concentration of a substance is directly proportional to the amount of light absorbed or inversely proportional to the logarithm of the transmitted light
What is the formula for Beer's Law?
A=Ebc
A=absorbance
E=Proportionality constant
b=length of cuvet in cm (usually 1)
c= concentration in mol/L
What are factors absorbance can vary with?
-Concentration
-pH
-temperature
What is the formula for measuring absorbance?
A=2-log%T

*remember you must first start with %T=I/Iox100
What are the assumptions Beer's Law makes?
-Light striking the solute is monochromatic--no stray light.
-Solute being analyzed is the only colored solute present in the solution
-light being measured comes only from the analytical beam of light.
What is the formula for an unknown glucose concentration of a patient?
conc(u)/conc(s)=abs(u)/conc(s)
Name the two types of light sources used in spectophotometry
Lamp
Laser
Name the most commonly used light source in spectophotometry and its corresponding wavelengths
tungsten or tungsten halogen
~320 to > 1000 nm which gives you visible and near IR regions
What are laser light sources mostly used for?
Hormones, drugs of abuse, and flourescents
What is a monochromator?
a system that isolates radiant energy of desired wavelength and excludes other wavelengths
In a monochromator, what is the degree of wavelenth isolation dependent on?
Entrance and exit slits
What defines the range of wavelengths that will be transmitted?
spectral bandpass
How does the size of the bandpass effect the monochromator?
The smaller the bandpass, the better. You get a more accurate Transmittance, and less interference
What are two fixed wavelength monochromators
-Colored glass(50nm bandwith, gives precision issues, not preffered)
-Interference filter (5-15nm bandwith, very precise)
What are the only kind of waves that can perform the spectromic function?
Harmonic waves
A linear non continuous spectrum, which gives no specific wavelength
Prism
-Linear, most widely used monochromator
-bandwith of 5-20nm
-blocks out all destructive waves to give only linear constructive waves
Diffraction grating
What type of detector works well with tungsten lamps?
PMT Photmultiplier tubes
What does a detector do?
converts light energy into electrical energy
What does Bichromatic Analysis do?
Splits the light beam in two and selects a different wavelength for each beam
What is the method in Bichromatic analysis?
-One wavelength is desired peak (analyte of interest)
-second wavelength is not absorbed by the analyte but is absorbed byt the interfering chromagen (complimentary wavelength)
Second wavelength is subtracted from first to get concentration of analyte.
Can Bichromatic analysis be used in lipemic and hemolyzed samples?
No. In lipemic samples a lipid panel must be done first on the serum.
In hemolyzed samples must be rejected for K and other analytes because of the substances released.