Laboratory Methods Flashcards
AMR, CRR
AMR: Analytical measurement range; reflects the instrument’s performance
CRR: Clinically reportable range; also includes pre-treatments to reflect patient’s actual values
Beer’s law
Absorbance = a (molar absorptivity) * b (path length) * c (concentration)
Transmittance is inversely related to absorbance
Nephelometry
Measures dispersal of light at specific angles, usually due to formation of antigen-antibody complexes.
Chromatography: Standard vs reverse
Standard: Nonpolar mobile phase, polar stationary phase
Reverse: Polar mobile phase (eg Water), nonpolar stationary phase
Ion exchange chromatography
Affinity exchange chromatography
Ion: Stationary phase is charged, usually negative.
Affinity: Protein interaction (eg Staph A, immunoglobin). Change pH to elute adsorbant.
Protein electrophoresis
Negatively charged proteins migrate towards positive anode.
Using stronger ionic strength slows migration but sharpens bands.
CEDIA
Competitive 1-step method
DIRECT RELATIONSHIP
Enzyme donor attached to reagent antigen. Patient (test) antigen frees ED-Ag to react with enzyme acceptor.
Stokes shift
Difference between excitation and emission wavelengths
Time-resolved fluorescent imunoassay
Long fluorescence, long exposure. Increases fluorescence signal compared to background.
EMIT
Competitive 1-step method
DIRECT RELATIONSHIP
Enzyme labeled drug competes with patient (target) drug. Freed enzyme generates chromogen.
FPIA
Competitive 1-step method
INVERSE RELATIONSHIP
Antibody-bound reagent emits polarized light. Target drug displaces»_space; polarization signal is lost
Fern test
Nitrazine test
Fern test: PPM, more specific than nitrazine test.
Nitrazine test: Paper strip, quite sensitive and specific
For amniotic membrane rupture
Methods for Hgb/Hct
Hematology analyzer: Best; Hct is calculated by multiplying RBC counts by MCV.
Conductometry: Affected by electrolyte and protein concentrations.
POC Glucose measurement
Has an inverse relationship with hematocrit (underestimates fetal glucose)
Not appropriate for primary diagnosis.
LOINC
Database and universal standard for lab observations
Send observations using a coding protocol like HL7
