FISCHBACH'S A MANUAL OF
LABORATORY AND DIAGNOSTIC TESTS.
11TH EDITION
• AUTHOR(S)FRANCES FISCHBACH;
MARGARET FISCHBACH; KATE STOUT
TESTBANKS
Ch. 1 — Diagnostic Testing
1) Stem: A nurse receives a chemistry report showing a
potassium of 6.1 mEq/L on a patient whose IV site was noted to
be difficult and whose blood sample was visibly hemolyzed. The
patient has no ECG changes and is asymptomatic. Which is the
best immediate nursing action?
A. Notify the provider and request emergent potassium-
lowering measures.
B. Repeat the blood draw from a new site and send a non-
hemolyzed specimen.
C. Document the result and continue routine monitoring since
the patient is asymptomatic.
,D. Prepare the patient for urgent dialysis per critical potassium
protocol.
Correct answer: B
Rationales
Correct (B): Hemolysis can artificially raise measured
potassium. Repeating the draw with proper technique will
determine whether the hyperkalemia is true. The textbook
emphasizes identifying preanalytic causes (hemolysis) before
acting on potentially spurious critical values.
A: Premature treatment for hyperkalemia without confirming
the value risks harm; treatment is indicated for true or
symptomatic hyperkalemia.
C: Documentation alone neglects the possibility of a lab artifact
that requires confirmation.
D: Dialysis is reserved for severe, refractory hyperkalemia or
specific clinical indications, not an unconfirmed lab artifact.
Teaching point: Always consider preanalytic causes (e.g.,
hemolysis) and confirm unexpected critical results.
Citation: Fischbach, F., Fischbach, M., & Stout, K. (2024). A
Manual of Laboratory and Diagnostic Tests (11th ed.). Ch. 1.
Ch. 1 — Diagnostic Testing
2) Stem: A rapid influenza antigen test performed in the
emergency department is negative in a patient with 12 hours of
influenza-like illness during local high community prevalence.
,According to diagnostic test principles, which interpretation is
most appropriate?
A. A negative rapid antigen definitively excludes influenza.
B. False negatives are possible; consider confirmatory PCR if
clinical suspicion remains high.
C. A negative antigen in high prevalence indicates the test's
specificity is low.
D. Treat as bacterial infection because viral testing is negative.
Correct answer: B
Rationales
Correct (B): Rapid antigen tests have lower sensitivity than PCR,
especially early in illness; the textbook highlights that negative
results do not rule out disease when clinical suspicion and
prevalence are high. Confirmatory testing or clinical judgment is
required.
A: This overstates negative predictive value; sensitivity
limitations can produce false negatives.
C: Specificity refers to false positives; a negative result is linked
to sensitivity, not low specificity.
D: A negative rapid viral test does not imply bacterial etiology
and should not automatically drive antibiotic therapy.
Teaching point: Consider test sensitivity, pretest probability,
and confirmatory testing when suspicion is high.
Citation: Fischbach, F., Fischbach, M., & Stout, K. (2024). A
Manual of Laboratory and Diagnostic Tests (11th ed.). Ch. 1.
, Ch. 1 — Diagnostic Testing
3) Stem: A patient on continuous heparin infusion has an
activated partial thromboplastin time (aPTT) of 48 seconds
(facility therapeutic range 60–90 s). The nurse notes the lab
specimen was collected 2 minutes after a heparin bolus. What
is the best interpretation and next step?
A. Accept the result; adjust heparin to reach therapeutic range
immediately.
B. Recognize timing may have yielded falsely low aPTT; repeat
specimen at steady-state.
C. Stop the heparin infusion immediately because the patient is
overanticoagulated.
D. Document and continue current infusion because aPTT is
within normal limits.
Correct answer: B
Rationales
Correct (B): Timing of specimen relative to dosing and infusion
rate can affect aPTT; the chapter stresses appropriate specimen
timing and communication with the lab to avoid misleading
results. Repeating at steady state will clarify anticoagulation.
A: Adjusting based on potentially timing-affected result risks
over- or under-anticoagulation.
C: The value is low, not high; stopping heparin for
overanticoagulation is not indicated.
D: The aPTT is below the facility therapeutic range for heparin
LABORATORY AND DIAGNOSTIC TESTS.
11TH EDITION
• AUTHOR(S)FRANCES FISCHBACH;
MARGARET FISCHBACH; KATE STOUT
TESTBANKS
Ch. 1 — Diagnostic Testing
1) Stem: A nurse receives a chemistry report showing a
potassium of 6.1 mEq/L on a patient whose IV site was noted to
be difficult and whose blood sample was visibly hemolyzed. The
patient has no ECG changes and is asymptomatic. Which is the
best immediate nursing action?
A. Notify the provider and request emergent potassium-
lowering measures.
B. Repeat the blood draw from a new site and send a non-
hemolyzed specimen.
C. Document the result and continue routine monitoring since
the patient is asymptomatic.
,D. Prepare the patient for urgent dialysis per critical potassium
protocol.
Correct answer: B
Rationales
Correct (B): Hemolysis can artificially raise measured
potassium. Repeating the draw with proper technique will
determine whether the hyperkalemia is true. The textbook
emphasizes identifying preanalytic causes (hemolysis) before
acting on potentially spurious critical values.
A: Premature treatment for hyperkalemia without confirming
the value risks harm; treatment is indicated for true or
symptomatic hyperkalemia.
C: Documentation alone neglects the possibility of a lab artifact
that requires confirmation.
D: Dialysis is reserved for severe, refractory hyperkalemia or
specific clinical indications, not an unconfirmed lab artifact.
Teaching point: Always consider preanalytic causes (e.g.,
hemolysis) and confirm unexpected critical results.
Citation: Fischbach, F., Fischbach, M., & Stout, K. (2024). A
Manual of Laboratory and Diagnostic Tests (11th ed.). Ch. 1.
Ch. 1 — Diagnostic Testing
2) Stem: A rapid influenza antigen test performed in the
emergency department is negative in a patient with 12 hours of
influenza-like illness during local high community prevalence.
,According to diagnostic test principles, which interpretation is
most appropriate?
A. A negative rapid antigen definitively excludes influenza.
B. False negatives are possible; consider confirmatory PCR if
clinical suspicion remains high.
C. A negative antigen in high prevalence indicates the test's
specificity is low.
D. Treat as bacterial infection because viral testing is negative.
Correct answer: B
Rationales
Correct (B): Rapid antigen tests have lower sensitivity than PCR,
especially early in illness; the textbook highlights that negative
results do not rule out disease when clinical suspicion and
prevalence are high. Confirmatory testing or clinical judgment is
required.
A: This overstates negative predictive value; sensitivity
limitations can produce false negatives.
C: Specificity refers to false positives; a negative result is linked
to sensitivity, not low specificity.
D: A negative rapid viral test does not imply bacterial etiology
and should not automatically drive antibiotic therapy.
Teaching point: Consider test sensitivity, pretest probability,
and confirmatory testing when suspicion is high.
Citation: Fischbach, F., Fischbach, M., & Stout, K. (2024). A
Manual of Laboratory and Diagnostic Tests (11th ed.). Ch. 1.
, Ch. 1 — Diagnostic Testing
3) Stem: A patient on continuous heparin infusion has an
activated partial thromboplastin time (aPTT) of 48 seconds
(facility therapeutic range 60–90 s). The nurse notes the lab
specimen was collected 2 minutes after a heparin bolus. What
is the best interpretation and next step?
A. Accept the result; adjust heparin to reach therapeutic range
immediately.
B. Recognize timing may have yielded falsely low aPTT; repeat
specimen at steady-state.
C. Stop the heparin infusion immediately because the patient is
overanticoagulated.
D. Document and continue current infusion because aPTT is
within normal limits.
Correct answer: B
Rationales
Correct (B): Timing of specimen relative to dosing and infusion
rate can affect aPTT; the chapter stresses appropriate specimen
timing and communication with the lab to avoid misleading
results. Repeating at steady state will clarify anticoagulation.
A: Adjusting based on potentially timing-affected result risks
over- or under-anticoagulation.
C: The value is low, not high; stopping heparin for
overanticoagulation is not indicated.
D: The aPTT is below the facility therapeutic range for heparin
