Year one review Flashcards
Direct ISE
what
composed of and types
application
measures ion concentration directly from sample
Electrodes and membranes
Glass Electrodes- for Na ions
Ion exchange electrodes- K ions
Membrane - selectively permeable
Glass membrane - permeable to Na ions
Polymer membrane- for K only
Clinical application of ISE
EMERG OR critical care
indirect ISE
what electrodes
membranes
dis/ad
measures ion concentration indirectly by measuring conductivity or total ionic strength first
electrodes - more componenets than direct ise
membranes- measures OVERALL conductivity
advan-less affected by turbidity
disadvan - less precise
HIGH hct means
serum ____ is higher than whole blood
less plasma so less CL
serum CL is higher because it is the extracellular fluid compartment where chloride is concentrated
good to know where hct levels are abnormal can affect CL especially if the wrong RI is used
What is Anion gap
Anion Gap (mmol/L) = [Sodium] – ([Chloride] + [Bicarb])
identifies electrolytes and acid base disorders (DKA), metabolic acidosis
need to calibrate instrument regularly because K, Na and CO3 need to be measured precisely
-be sure to verify against known standards
-if you track anion gap over time you can ID trends or deviations from expected values which would be an issue with testing or instrumentation
-be sure to participate in proficiency testing
if anion gap falls out of range what does it signal
reagent degradation , calibration errors, deviation from procedure
high anion gap - DKA, LA, renal failure due to accumulation of acids or unmeasured anions
normal anion gap MA - diarrhea, loss of CO3 but not increase of other ions
What do you do when reviewing a delta alert
- review results, pt history and sample handling procedures
contamination, incorrect collections, reagent issues,
by looking at delta check patterns labs can identify systemic patterns
calibrators vs standards
Calibrators have known concentrations used to adjust and verify the accuracy of an instrument. –helps to establish a relationship between the instrument’s output and the actual analyte concentration
-creates a calibration curve
Standards- have well-established and validated concentrations
or values, used as references for comparison
-used to check the ongoing accuracy
of test results but are not used to adjust the instrument.
Calibration drift
gradual deviation from true value
wear and tear, environmental changes, reagent degradation , humidity
helps to calibrate regularly
interpreting calibration curves
relationship between calibrator and instrument
-curve should be linear
-slope is the sensitivity of the instrument
-if there is a deviation then recalibrate
-calibration verifies the intrument accuracy to match known RI
QC is
monitoring ongoing accuracy and precision
What is osmolal gap
difference between measured OSMO and calculated OSM. detects unmeasured osmo active substances in the blood
(2*[sodium]) + [Glucose] + [urea] -used when there are unmeasured substances
used for detecting toxins (alcs) , poisoning, metabolic conditions
increased - presence of unmeasured osmotically active substances - investigate further
normal osmolal gap means you have nothing additional in your system just NA, GLUR, UREA
edta and interferences
binds CA to prevent clotting
CA/MG bind EDTA so you cant use edta to measure them
enzyme activities - enzyme assays that need calcium as a cofactor will be affected
Heparin and interferences
activates antithrombin III, inhibits thrombin and prevents clot formation
-used for plasma biochem tests like electrolytes and glucose
interference
lithium heparin - can artifically increase lithium and sodium heparin can increase sodium
falsely low calcium - heparin can bind to calcium mostly in calcium tests, causing inaccurate results.
citrate and interferences
binds calcium to prevent clotting - forms calcium citrate complexes
-interferences
Ca/Mg: citrate binds CA so it cant be used for tests that need CA or MG testing
Dilution effect- liquid ANTICOAG can dilute the sample and lead to falsely low concentrations
Oxalate/Fluoride and interferences
oxalate precipitates Ca and fluoride inhibits glycolysis
-used for glucose and lactate levels
interfernces -
Ca just like EDTA and citrate - affects ca measurement
Enzyme Assay - fluoride inhibits enzyme reactions so that will affect tests that rely on enzymatic methods
Colorimeteric testing
quantifies analytes based on color changes resulting from chemical reactions with specific reagents, intensity of color is proportional to concentration of analyte
-dilute or treat to remove interfering substances
-measurement with a spectrophotometer at a specific wavelength
-compared against a calibration curve
glucose w/ glucose oxidase
Tp with Biuret method
Bilirubin assay for LFT
susceptible to interference from hemolysis, lipemia, and other sample conditions
reflectomertry
-measured intensity of light reflected from colored surface to determine concentration on analyte
-sample applied to a test strip with reagents
reflectometer measures intensity of light reflected from colored area of test strip where analyte was placed
POCT with test strips
urine dipstick tests for glucose, protein, ketones
Limitations- dependent on quality of test strips and interference from contaminants
refractometry
how is it done and what is it affected by
measures refractive index of a sample which changes the concertation of a solute
-used to determine protein concentration in serum and specific gravity of urine
-use a refractometer
-refractive index is read on a calibrated scale which correlates with analyte concentration
-used to measure serum protein
-measure USPG to assess kidney function
-affected by temperature , needs a temp correction
Nephelometry
how is it done and what is it affected by
-measures light scattered in particles in suspension
-amount of light scattered is directly proportional to concentration of particles good for measuring quantifying proteins or immune complexes
-sample mixed with reagent that forms insoluble particles
-measures intensity of light scattered at a specific angle which is compared to a calibration curve to determine analyte concentration
-used to quantify proteins in serum - IGG, or for immunology
-good for proteins or immunoassay
-affected by high lipid levels or particulates
turbidimetry
how is it done and what is it affected by
-measures reduction in light transmission due to particles suspended in a liquid different nephelometry by measuring the decrease in light passing through the sample rather than the scattered light.
-analyte + reagent form precipitate or suspension measure decrease of light with turbidimeter and compare the reduction to a calibration curve
good for bacteria concentration in culture or clot formation in COAG
-less sensitive than nephelometry for detecting low concentrations
sandwich immunoassay
how is it done and what is it affected by
-highly specific to detect AG in sample
-bind an AG to two AB : capture and detection AB = making a sandwich
Capture AB coating - a solid surface (microtiter) coated with AB specific to target AG
-target AG binds to capture AB
- detection AB conjugated to an enzyme or
fluorescent marker is added, binding to another site on the antigen
-substrate for the enzyme is added producing a signal (colorimetric, fluorescent, or luminescent). measure intensity of signal to STANDARD curve
good for detecting hormones (TSH, hCG)
measuring biomarkers (TNIHS)
limitation - needs multiple AB and can be time consuming
competitive immunoassay
method
application
ad/dis
measure AG concentration by competing with a labeled AG for a limited number of AB binding sites. The signal produced is inversely
proportional to the concentration of the target AG in the sample. Intensity of signal compared with standard curve
Good for measuring small molecules - drugs hormones , detecting AB in autoimmune diseases
DIS- Inverse signal relationship requires careful interpretation.
Which quality control measure is most critical in ensuring accurate electrolyte testing
results on an ISE analyzer
Monitoring internal quality control results for trends or shifts
After a recent calibration, the ISE analyzer reports unusually high sodium levels in all
patient samples. Which of the following is the most likely cause?
Incorrect preparation of the calibration solution
Incorrect calibration solution preparation can cause systematic errors across all tests
Which of the following would most likely indicate a quality control issue with electrolyte
testing in the analytical phase
Sudden shifts in control values without a change in reagents or equipment
Unexpected shifts in QC values suggest an issue with the testing process or equipment, warranting investigation to maintain accurate results
a gradual shift suggests?
potential maintenance or
calibration issue. Reviewing the logs for missed procedures can help identify if a lack of
proper maintenance is causing the drift
External Quality Assurance (EQA)
systematic approaches designed to monitor and assess performance of labs and compare them to other labs
Regular Assessment:
Benchmarking:
Feedback and Improvement:
Regulatory Compliance:
Regular Assessment:
EQA programs are done regularly (quarterly, annually) where labs submit test results for standardized samples to compare with other labs and establish RI
Benchmarking:
performance metrics- evaluated based on ability to produce results that are in ranges with other labs - identifies areas where they can improve
Feedback and Improvement:
reports - detailed feedback
CA- labs need to take corrective actions to address issues and improve processes
Regulatory Compliance
standards- making sure lab standards align with global guidelines
accreditation - needed for certification
What is potentiometry
Potential develops at measuring (indicator) electrode
-membrane molecules selectively bind measuring IONS and there is a potential measured with voltmeter
-Reference potential compared to potential at measuring electrode: Nernst equation: expresses potential as related to activity of analyte
- Activity of ion is converted to concentration in mmol/L
DIS-protein build-up on electrodes: decreases life span
