Diagnostic Methods & Technologies Flashcards

According to Beer's law, absorbance measured in a spectrophotometer is directly proportional to which variable when path length is held constant?

Answer: Concentration of the absorbing substance

Beer's law states A = abc, so absorbance rises linearly with concentration at a fixed path length and molar absorptivity.

How does nephelometry differ from turbidimetry when measuring immune complexes?

Answer: Nephelometry measures light scattered at an angle from the incident beam

Nephelometry detects light scattered at an angle, while turbidimetry measures the loss of light transmitted in line with the beam.

An ion-selective electrode with a valinomycin membrane is used to measure which analyte?

Answer: Potassium

Valinomycin is an ionophore that selectively binds potassium ions.

A severely lipemic specimen gives a falsely low sodium on an indirect ISE but a normal result on a direct ISE. What explains this?

Answer: The electrolyte exclusion effect from the increased nonaqueous plasma volume

Indirect ISEs dilute the total plasma volume, so excess lipid or protein displacing water causes pseudohyponatremia, while direct ISEs measure activity in plasma water.

In a competitive fluorescence polarization immunoassay, what happens to the polarization signal as patient analyte concentration increases?

Answer: Polarization decreases

More patient analyte displaces labeled tracer from the antibody, and the free tracer rotates rapidly, which lowers polarization.

In atomic absorption spectrophotometry, the hollow cathode lamp is made of which material?

Answer: The same element as the analyte being measured

The cathode is made of the analyte element so it emits that element's specific resonance wavelengths.

In freezing point depression osmometry, how much does 1 osmole of solute per kilogram of water lower the freezing point?

Answer: 1.86 °C

The molal freezing point constant of water is 1.86 °C per osmol/kg.