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100+ Free DABCC Practice Questions
Diplomate of the American Board of Clinical Chemistry practice questions are available now; exam metadata is being verified.
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Sample DABCC Practice Questions
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1According to the Beer-Lambert law (A = εbc), if all else is held constant, absorbance is directly proportional to which of the following?
A.The path length and the analyte concentration
B.The wavelength of incident light only
C.The transmittance of the solution
D.The temperature of the cuvette
Explanation: Beer's law states A = εbc, where ε is the molar absorptivity, b is the path length, and c is the concentration. Therefore absorbance increases linearly with both path length and analyte concentration when ε and the wavelength are fixed.
2In high-performance liquid chromatography (HPLC) using a reversed-phase C18 column, which analyte characteristic causes the longest retention time?
A.High polarity and water solubility
B.High hydrophobicity (nonpolar character)
C.High ionic charge at the mobile-phase pH
D.Low molecular weight only
Explanation: In reversed-phase HPLC the stationary phase (C18) is nonpolar and the mobile phase is polar. More hydrophobic (nonpolar) analytes partition into the stationary phase and are retained longer, eluting last.
3In tandem mass spectrometry (LC-MS/MS), what does multiple reaction monitoring (MRM) measure to achieve high specificity?
A.Only the molecular weight of the intact analyte
B.Total ion current across the full mass range
C.A specific precursor ion fragmented to a specific product ion transition
D.The UV absorbance of eluting peaks
Explanation: MRM (also called selected reaction monitoring) selects a precursor ion in the first quadrupole, fragments it in the collision cell, and monitors a specific product ion in the third quadrupole. This precursor-to-product transition provides high analytical specificity.
4Serum protein electrophoresis on agarose gel at alkaline pH separates proteins primarily on the basis of which property?
A.Isoelectric point measured directly
B.Molecular weight alone
C.Hydrophobicity
D.Net surface charge (charge-to-size ratio)
Explanation: In zone electrophoresis at alkaline pH, serum proteins carry a net negative charge and migrate toward the anode based on their charge-to-size ratio. Albumin, the most negatively charged, migrates fastest.
5In a competitive immunoassay, how does the measured signal relate to analyte concentration in the patient sample?
A.Directly — signal increases as analyte increases
B.Inversely — signal decreases as analyte concentration increases
C.There is no relationship between signal and concentration
D.Signal is always constant regardless of analyte
Explanation: In a competitive immunoassay, labeled analyte competes with patient analyte for limited antibody binding sites. More patient analyte displaces labeled analyte, so the measured signal is inversely proportional to analyte concentration.
6A patient with very high triglycerides shows a falsely low sodium on an indirect ion-selective electrode (ISE) analyzer but a normal value on a direct ISE. This phenomenon is best described as:
A.Analytical bias from hemolysis
B.True dilutional hyponatremia
C.Pseudohyponatremia due to electrolyte exclusion effect
D.An ISE membrane failure
Explanation: Indirect ISE methods dilute the sample and assume a normal plasma water fraction (~93%). When lipids or proteins increase the solid phase, the aqueous fraction falls, producing falsely low sodium (pseudohyponatremia). Direct ISE measures activity in plasma water and is unaffected.
7In gas chromatography (GC), which detector is most appropriate for quantifying volatile alcohols such as ethanol, methanol, and isopropanol?
A.Refractive index detector
B.Electron capture detector (ECD)
C.UV-visible detector
D.Flame ionization detector (FID)
Explanation: The flame ionization detector responds to carbon-containing (organic) compounds and is the standard detector for volatile alcohols by headspace GC. It offers a wide linear range and high sensitivity to hydrocarbons.
8The high-dose hook effect in a noncompetitive (sandwich) immunoassay produces what result?
A.A falsely low result when analyte concentration is extremely high
B.A falsely high result at low concentrations
C.No effect on results at any concentration
D.A consistent positive bias across the range
Explanation: At extremely high analyte concentrations, both capture and detection antibodies become saturated by free analyte before the sandwich forms, reducing the signal. This produces a paradoxically low result despite very high true concentration.
9Which wavelength region of light is associated with the highest energy and shortest wavelength used in a clinical spectrophotometer?
A.Near-infrared (~750-1400 nm)
B.Visible (~400-700 nm)
C.Ultraviolet (~200-380 nm)
D.Infrared (>2000 nm)
Explanation: Energy is inversely proportional to wavelength (E = hc/λ). Ultraviolet light has the shortest wavelengths (~200-380 nm) and therefore the highest energy of the options listed.
10Matrix effects in LC-MS/MS, such as ion suppression, are best monitored and corrected by which strategy?
A.Eliminating the chromatographic step entirely
B.Increasing the injection volume
C.Switching to a longer UV wavelength
D.Use of a stable isotope-labeled internal standard
Explanation: A stable isotope-labeled internal standard co-elutes with and behaves chemically like the analyte, experiencing the same ion suppression. Normalizing the analyte peak to this internal standard corrects for matrix effects.
About the DABCC Practice Questions
Verified exam format metadata for Diplomate of the American Board of Clinical Chemistry is pending. The practice questions above remain available while official exam length, timing, passing score, fee, and administrator details are reviewed.