Weekly Pathology Exam - June 19, 2026 (Section A: MCQs)

Question 1

A 62-year-old man with COPD is brought in with confusion. ABG: pH 7.28, PaCO₂ 64 mmHg, HCO₃⁻ 28 mmol/L. Which is the most likely primary disorder?

Accepted Answer

Respiratory acidosis — The pH is low (acidemia), and the PaCO₂ is high (respiratory compensation for metabolic alkalosis or primary respiratory acidosis). Given the history of COPD, chronic retention of CO₂ is likely, and this acute exacerbation has worsened it, leading to respiratory acidosis. The HCO₃⁻ is elevated but not sufficiently to normalize the pH, indicating a metabolic compensation for the respiratory acidosis.

Question 2

A 28-year-old woman with vomiting presents with cramps. ABG: pH 7.54, PaCO₂ 48 mmHg, HCO₃⁻ 38 mmol/L. Which is the best interpretation?

Accepted Answer

Metabolic alkalosis with respiratory compensation — The pH is high (alkalemia), and the HCO₃⁻ is high (metabolic alkalosis). The PaCO₂ is also elevated, which is a compensatory mechanism for metabolic alkalosis. Vomiting leads to loss of gastric acid, causing metabolic alkalosis. The body attempts to compensate by retaining CO₂.

Question 3

A 45-year-old diabetic in DKA: ABG: pH 7.18, PaCO₂ 24 mmHg, HCO₃⁻ 9 mmol/L; Na⁺ 138, Cl⁻ 100, HCO₃⁻ 9. What is the most likely acid-base disorder?

Accepted Answer

Metabolic acidosis with respiratory compensation — The pH is low (acidemia), and the HCO₃⁻ is low (metabolic acidosis). The PaCO₂ is low, indicating hyperventilation as a compensatory mechanism to blow off CO₂. Diabetic ketoacidosis is a classic cause of metabolic acidosis.

Question 4

A 70-year-old man with vomiting and nasogastric suction: ABG: pH 7.50, PaCO₂ 54 mmHg, HCO₃⁻ 40 mmol/L. Which is correct?

Accepted Answer

Primary metabolic alkalosis with partial respiratory compensation. — The pH is high (alkalemia) and the HCO₃⁻ is high (metabolic alkalosis). The PaCO₂ is also elevated, which is respiratory compensation for metabolic alkalosis. Vomiting and NG suction lead to loss of gastric acid, causing metabolic alkalosis.

Question 5

A trauma patient: ABG: pH 7.10, PaCO₂ 35 mmHg, HCO₃⁻ 10 mmol/L. Using Winter's formula, expected PaCO₂ for this HCO₃⁻ is approximately? (choose closest)

Accepted Answer

30 mmHg — Winter's formula for expected PaCO₂ in metabolic acidosis is: Expected PaCO₂ = (1.5 HCO₃⁻) + 8 ± 2. So, (1.5 10) + 8 = 15 + 8 = 23 ± 2. The closest value among the options is 20 mmHg, which suggests adequate respiratory compensation. The actual PaCO₂ of 35 mmHg is higher than expected, suggesting a mixed disorder or inadequate compensation.

Question 6

A patient's electrolytes: Na⁺ 140, K⁺ 4.2, Cl⁻ 102, HCO₃⁻ 8. Calculate anion gap (AG = Na - (Cl + HCO₃)). Which is the AG?

Accepted Answer

14 mmol/L — Anion Gap (AG) = Na⁺ - (Cl⁻ + HCO₃⁻) = 140 - (102 + 8) = 140 - 110 = 30 mmol/L. However, the options provided are all lower. Let's re-evaluate the typical normal anion gap which is around 8-16 mmol/L. If the question intends to calculate the gap with the provided numbers, then 140 - (102 + 8) = 30. There might be a typo in the provided data or options. Assuming the options are correct and there might be a different interpretation or formula intended, or if the provided values lead to a specific interpretation within a diagnostic context.

Question 7

A 50-year-old with chronic COPD: ABG: pH 7.36, PaCO₂ 56 mmHg, HCO₃⁻ 32 mmol/L. Best interpretation?

Accepted Answer

Compensated chronic respiratory acidosis — The pH is normal (7.36), indicating compensation. The PaCO₂ is elevated (56 mmHg), consistent with chronic respiratory acidosis. The HCO₃⁻ is also elevated (32 mmol/L), indicating metabolic compensation for the chronic respiratory acidosis. This represents a compensated state.

Question 8

A septic patient: ABG: pH 7.25, PaCO₂ 28 mmHg, HCO₃⁻ 12 mmol/L; electrolytes: Na 140, Cl 100, HCO₃ 12. AG = 28. Delta ratio: ΔAG = (28-12) = 16, ΔHCO₃ = (24-12) = 12. What is ΔAG/ΔHCO₃ and its interpretation?

Accepted Answer

1.33; Indicates pure metabolic acidosis — The delta ratio is calculated as ΔAG / ΔHCO₃. The normal anion gap is assumed to be around 12, and normal HCO₃ is 24. So, ΔAG = 28 - 12 = 16, and ΔHCO₃ = 24 - 12 = 12. Therefore, ΔAG/ΔHCO₃ = 16/12 = 1.33. A delta ratio between 1 and 2 suggests a pure high anion gap metabolic acidosis with appropriate compensation.

Question 9

A patient with salicylate overdose: early ABG: pH 7.55, PaCO₂ 26 mmHg, HCO₃⁻ 22 mmol/L. Which best describes this?

Accepted Answer

Respiratory alkalosis — In early salicylate overdose, the primary effect is respiratory alkalosis due to direct stimulation of the respiratory center. The pH is high (7.55) and the PaCO₂ is low (26 mmHg). The HCO₃⁻ is normal, indicating no significant metabolic compensation or primary metabolic derangement yet.

Question 10

ABG: pH 7.10, PaCO₂ 70 mmHg, HCO₃⁻ 22 mmol/L. What is the best interpretation?

Accepted Answer

Respiratory acidosis with metabolic compensation — The pH is low (acidemia) and the PaCO₂ is high (70 mmHg), indicating respiratory acidosis. The HCO₃⁻ is normal, suggesting that this is an acute respiratory acidosis without significant metabolic compensation yet. The body's compensation for respiratory acidosis involves increasing HCO₃⁻.

Question 11

Patient with severe diarrhea: ABG: pH 7.32, PaCO₂ 34 mmHg, HCO₃⁻ 17 mmol/L. Which is most likely?

Accepted Answer

Metabolic acidosis with respiratory compensation — The pH is slightly low (7.32) and the HCO₃⁻ is low (17 mmol/L), indicating metabolic acidosis. The PaCO₂ is also low (34 mmHg), representing respiratory compensation (hyperventilation) to correct the acidosis. Severe diarrhea leads to loss of bicarbonate.

Question 12

Post-operative patient receiving large IV normal saline: ABG: pH 7.32, HCO₃⁻ 18 mmol/L, Na 140, Cl 108. What acid-base disturbance is likely?

Accepted Answer

Metabolic acidosis — Normal saline has a high chloride content. Infusion of large amounts of normal saline can lead to hyperchloremic metabolic acidosis. The low HCO₃⁻ (18 mmol/L) and normal pH suggest metabolic acidosis with some degree of respiratory compensation, or it's tending towards acidosis.

Question 13

A 55-year-old male presents to the emergency department with severe crushing chest pain radiating to his left arm and jaw, accompanied by cold sweats. Which cardiac biomarker is considered the gold standard for diagnosing his condition?

Accepted Answer

Troponin I — Cardiac troponins (Troponin I and Troponin T) are the most sensitive and specific biomarkers for myocardial injury. While both are excellent, Troponin I is often cited as the gold standard due to its higher specificity for cardiac muscle.

Question 14

A patient with suspected heart failure presents with dyspnea. Which biomarker would be MOST useful in differentiating between cardiac and non-cardiac causes of shortness of breath?

Accepted Answer

BNP (B-type Natriuretic Peptide) — BNP (and NT-proBNP) is elevated in heart failure due to ventricular stretch. In non-cardiac causes of dyspnea, BNP levels are typically normal or only mildly elevated, making it highly useful in distinguishing cardiac from non-cardiac causes.

Question 15

Which cardiac biomarker has the SHORTEST time to return to normal levels after myocardial infarction?

Accepted Answer

Myoglobin — Myoglobin is released into the bloodstream very early after myocardial injury and is cleared relatively quickly. It returns to baseline within 24-36 hours, making it useful for ruling out MI in the very early stages, but less useful for diagnosis later on.

Question 16

A 60-year-old woman presents 2 hours after onset of chest pain. Which cardiac biomarker would be elevated EARLIEST?

Accepted Answer

Myoglobin — Myoglobin is released into the circulation within minutes to a few hours of myocardial injury and is typically the first biomarker to become elevated, usually within 1-4 hours of symptom onset.

Question 17

What is the underlying pathophysiology of coronary artery disease?

Accepted Answer

Atherosclerosis, leading to plaque formation and narrowing of the coronary arteries — Coronary artery disease (CAD) is primarily caused by atherosclerosis, a process of plaque buildup within the coronary arteries, leading to reduced blood flow to the heart muscle. Thrombus formation is a complication of ruptured plaques, and inflammation of the myocardium or valvular issues are distinct conditions.

Question 18

Which clinical feature is characteristic of intermittent claudication in peripheral artery disease?

Accepted Answer

Pain in the legs that is triggered by exercise and relieved by rest — Intermittent claudication is characterized by muscle pain or cramping in the legs that occurs during physical activity (like walking) and is relieved by rest. This is due to inadequate blood supply to the muscles during increased demand.

Question 19

A patient presents with sudden numbness on the right side of the face, arm weakness, and difficulty speaking. What is the MOST likely diagnosis?

Accepted Answer

Stroke (Cerebrovascular Accident) — The sudden onset of focal neurological deficits, such as facial numbness, arm weakness, and speech difficulty, is highly suggestive of a stroke (Cerebrovascular Accident), which results from disruption of blood flow to the brain.

Question 20

Which diagnostic test records the electrical activity of the heart and can identify ischemia, arrhythmias, or previous heart attacks?

Accepted Answer

Electrocardiogram (ECG/EKG) — An Electrocardiogram (ECG or EKG) is a non-invasive test that records the electrical signals of the heart. It is crucial for detecting arrhythmias, signs of ischemia (lack of blood flow), and evidence of previous myocardial infarction.

Question 21

What is the primary advantage of NT-proBNP over BNP in diagnosing heart failure?

Accepted Answer

NT-proBNP has a longer half-life and is more stable — NT-proBNP (N-terminal pro-B-type natriuretic peptide) is a prohormone fragment. It has a longer half-life and is more stable in circulation than BNP, making it easier to assay and potentially more advantageous in certain clinical scenarios. Both are useful for heart failure diagnosis.

Question 22

A 45-year-old asymptomatic patient is found to have consistently elevated blood pressure readings over several visits. What is the MOST likely diagnosis?

Accepted Answer

Essential hypertension — Essential hypertension (also known as primary hypertension) is the most common type of high blood pressure, accounting for 90-95% of cases. It has no identifiable secondary cause and is often diagnosed in asymptomatic individuals with persistently elevated readings.

Question 23

Which imaging technique uses contrast dye and X-rays to visualize coronary arteries and identify blockages?

Accepted Answer

Coronary angiography — Coronary angiography (also called cardiac catheterization) is an invasive procedure where a catheter is guided to the coronary arteries, and contrast dye is injected to visualize them using X-rays. This allows for direct identification and assessment of blockages.

Question 24

A patient with heart failure presents with bilateral ankle edema, shortness of breath when lying flat, and fatigue. What mechanism explains the edema?

Accepted Answer

Increased interstitial fluid due to impaired venous return and fluid retention — In heart failure, the weakened heart cannot effectively pump blood. This leads to a backup of blood, increasing hydrostatic pressure in the capillaries, particularly in the lower extremities. Impaired kidney function and activation of the renin-angiotensin-aldosterone system also lead to sodium and water retention, further contributing to edema.

Question 25

A 55-year-old male presents to the emergency department with severe crushing chest pain radiating to his left arm and jaw, accompanied by cold sweats. Which cardiac biomarker is considered the gold standard for diagnosing his condition?

Accepted Answer

Troponin I — Cardiac troponins (Troponin I and Troponin T) are the most sensitive and specific biomarkers for myocardial injury. While both are excellent, Troponin I is often cited as the gold standard due to its higher specificity for cardiac muscle.

Question 26

A patient with suspected heart failure presents with dyspnea. Which biomarker would be MOST useful in differentiating between cardiac and non-cardiac causes of shortness of breath?

Accepted Answer

BNP (B-type Natriuretic Peptide) — BNP (and NT-proBNP) is elevated in heart failure due to ventricular stretch. In non-cardiac causes of dyspnea, BNP levels are typically normal or only mildly elevated, making it highly useful in distinguishing cardiac from non-cardiac causes.

Question 27

Which cardiac biomarker has the SHORTEST time to return to normal levels after myocardial infarction?

Accepted Answer

Myoglobin — Myoglobin is released into the bloodstream very early after myocardial injury and is cleared relatively quickly. It returns to baseline within 24-36 hours, making it useful for ruling out MI in the very early stages, but less useful for diagnosis later on.

Question 28

A 60-year-old woman presents 2 hours after onset of chest pain. Which cardiac biomarker would be elevated EARLIEST?

Accepted Answer

Myoglobin — Myoglobin is released into the circulation within minutes to a few hours of myocardial injury and is typically the first biomarker to become elevated, usually within 1-4 hours of symptom onset.

Question 29

What is the underlying pathophysiology of coronary artery disease?

Accepted Answer

Atherosclerosis, leading to plaque formation and narrowing of the coronary arteries — Coronary artery disease (CAD) is primarily caused by atherosclerosis, a process of plaque buildup within the coronary arteries, leading to reduced blood flow to the heart muscle. Thrombus formation is a complication of ruptured plaques, and inflammation of the myocardium or valvular issues are distinct conditions.

Question 30

Which clinical feature is characteristic of intermittent claudication in peripheral artery disease?

Accepted Answer

Pain in the legs that is triggered by exercise and relieved by rest — Intermittent claudication is characterized by muscle pain or cramping in the legs that occurs during physical activity (like walking) and is relieved by rest. This is due to inadequate blood supply to the muscles during increased demand.

Question 31

A patient presents with sudden numbness on the right side of the face, arm weakness, and difficulty speaking. What is the MOST likely diagnosis?

Accepted Answer

Stroke (Cerebrovascular Accident) — The sudden onset of focal neurological deficits, such as facial numbness, arm weakness, and speech difficulty, is highly suggestive of a stroke (Cerebrovascular Accident), which results from disruption of blood flow to the brain.

Question 32

Which diagnostic test records the electrical activity of the heart and can identify ischemia, arrhythmias, or previous heart attacks?

Accepted Answer

Electrocardiogram (ECG/EKG) — An Electrocardiogram (ECG or EKG) is a non-invasive test that records the electrical signals of the heart. It is crucial for detecting arrhythmias, signs of ischemia (lack of blood flow), and evidence of previous myocardial infarction.

Question 33

What is the primary advantage of NT-proBNP over BNP in diagnosing heart failure?

Accepted Answer

NT-proBNP has a longer half-life and is more stable — NT-proBNP (N-terminal pro-B-type natriuretic peptide) is a prohormone fragment. It has a longer half-life and is more stable in circulation than BNP, making it easier to assay and potentially more advantageous in certain clinical scenarios. Both are useful for heart failure diagnosis.

Question 34

A 45-year-old asymptomatic patient is found to have consistently elevated blood pressure readings over several visits. What is the MOST likely diagnosis?

Accepted Answer

Essential hypertension — Essential hypertension (also known as primary hypertension) is the most common type of high blood pressure, accounting for 90-95% of cases. It has no identifiable secondary cause and is often diagnosed in asymptomatic individuals with persistently elevated readings.

Question 35

Which imaging technique uses contrast dye and X-rays to visualize coronary arteries and identify blockages?

Accepted Answer

Coronary angiography — Coronary angiography (also called cardiac catheterization) is an invasive procedure where a catheter is guided to the coronary arteries, and contrast dye is injected to visualize them using X-rays. This allows for direct identification and assessment of blockages.

Question 36

A patient with heart failure presents with bilateral ankle edema, shortness of breath when lying flat, and fatigue. What mechanism explains the edema?

Accepted Answer

Increased interstitial fluid due to impaired venous return and fluid retention — In heart failure, the weakened heart cannot effectively pump blood. This leads to a backup of blood, increasing hydrostatic pressure in the capillaries, particularly in the lower extremities. Impaired kidney function and activation of the renin-angiotensin-aldosterone system also lead to sodium and water retention, further contributing to edema.

Question 37

A study of blood product therapy is done. One product is identified that carries the greatest risk for infection. This blood product has the shortest shelf life, and it must be used as quickly as possible for transfusion. Which of the following products is best described by these findings?

Accepted Answer

Platelets — Platelets have the shortest shelf life (typically 5 days under standard conditions, sometimes up to 7 days with apheresis platelets and special storage) and are prone to bacterial contamination and growth due to their storage temperature (room temperature) and higher risk of bacterial colonization from the donor. They must be used quickly after collection.

Question 38

A 17-year-old boy has developed a mild fever with sore throat over the past day. On physical examination he has generalized lymphadenopathy. Laboratory studies show a CD4 lymphocyte count of 375/microliter. He is most likely to be infected with which of the following agents?

Accepted Answer

HIV — The symptoms (fever, sore throat, lymphadenopathy) combined with a CD4 count of 375/microliter are highly suggestive of acute primary HIV infection (seroconversion illness). While EBV can cause similar symptoms, the CD4 count in the context of HIV is a critical differentiator.

Question 39

A healthy 27 year old male donates blood. He completes the questionnaire and interview with no exclusions noted. The presence of which of the following infectious agents will not routinely tested for on his blood collected for transfusion?

Accepted Answer

Human T-lymphotropic virus type 1 (HTLV-1) — While HIV-1, HCV, and WNV are routinely tested for in blood donations in many regions, routine screening for HTLV-1 is not universally mandated for all blood donations, though it may be done in specific circumstances or regions. Guidelines can vary.

Question 40

During phlebotomy, there is difficulty obtaining blood for all of the test ordered. Not all of the collection tubes are completely filled. Of the following collection tubes, which is the only one that may be partially filled and not affect test results?

Accepted Answer

SST (Serum Separator Tube) — SST tubes contain a gel separator. As long as the tube is filled to allow for proper clot formation and separation, a partial fill may not significantly impact serum chemistry results. However, tubes with additives like EDTA (for CBC) and sodium citrate (for coagulation studies) require specific fill volumes (ratio of anticoagulant to blood) to ensure accurate results. Underfilling EDTA tubes can cause cell lysis, and underfilling sodium citrate tubes can lead to falsely prolonged coagulation times.

Question 41

A 25-year-old woman incurs a head injury from a skiing accident. She is now in stable condition and her vital signs are normal. Serum electrolytes now show Na 134 meq/L, K 7.6 meq/L, Cl 100 meq/L, and CO2 25 meq/L. What is the most likely etiology for these laboratory test findings?

Accepted Answer

Hemolyzed specimen — The markedly elevated potassium (7.6 meq/L) in the presence of a normal or slightly low sodium and normal CO2 is highly suggestive of a hemolyzed specimen. Red blood cell lysis releases intracellular potassium into the serum, leading to falsely elevated potassium levels. Other electrolyte abnormalities like hyponatremia and hypernatremia seen in DI or SIADH, or adrenal insufficiency, would not typically present with such a dramatic and isolated hyperkalemia without other specific findings.

Question 42

What neurotransmitter is associated with runner's high?

Accepted Answer

Endorphins — Endorphins are endogenous opioid peptides that are released during strenuous exercise, such as running, and are believed to contribute to the euphoric feeling known as 'runner's high'.

Question 43

What neurotransmitter is associated with anxiety disorders?

Accepted Answer

All of the above — GABA is the primary inhibitory neurotransmitter in the central nervous system, and its reduced activity is linked to anxiety. Serotonin and norepinephrine also play significant roles in mood regulation and stress response, and imbalances in these neurotransmitters are associated with anxiety disorders.

Question 44

Where do neurons store the genetic information they use to code and build all the proteins required for their functions?

Accepted Answer

Nucleus — The nucleus of a neuron contains the cell's DNA, which holds the genetic blueprints (genes) for all the proteins the neuron needs to function. This genetic information is transcribed into RNA and then translated into proteins, often at ribosomes.

Question 45

Which of the following are major inhibitory neurotransmitters, causing inhibitory postsynaptic potentials (IPSPs)?

Accepted Answer

GABA and Glycine — GABA (Gamma-aminobutyric acid) and Glycine are the primary inhibitory neurotransmitters in the central nervous system. They bind to receptors that open ion channels, leading to hyperpolarization of the postsynaptic membrane, thus inhibiting neuronal firing.

Question 46

The effect of tetrodotoxin (puffer fish poison) on axons demonstrates

Accepted Answer

The role of voltage-gated sodium channels in action potential generation — Tetrodotoxin (TTX) specifically blocks voltage-gated sodium channels. By preventing the influx of sodium ions, it inhibits the generation and propagation of action potentials, thereby demonstrating the critical role of these channels in nerve impulse conduction.

Question 47

What neurotransmitter is associated with mood disorders?

Accepted Answer

All of the above — While serotonin is most famously linked to mood disorders like depression, dopamine and norepinephrine also play significant roles. Imbalances in all three of these monoamine neurotransmitters are implicated in the pathophysiology of various mood disorders.

Question 48

Which of the following is not true?

Accepted Answer

GABA is an excitatory neurotransmitter. — GABA (Gamma-aminobutyric acid) is the principal inhibitory neurotransmitter in the central nervous system. Glutamate is the primary excitatory neurotransmitter.

Question 49

What neurotransmitter is associated with insomnia?

Accepted Answer

Serotonin — While GABA is inhibitory and generally promotes sleep, serotonin levels are complex. Low levels of serotonin are often associated with depression and can also contribute to insomnia, as serotonin plays a role in regulating sleep-wake cycles. Melatonin is a hormone that regulates sleep. Histamine promotes wakefulness, so low histamine would be associated with sleep, not insomnia.

Question 50

What neurotransmitter is associated with seizures?

Accepted Answer

Both B and C — Seizures are characterized by excessive neuronal excitation. An imbalance favoring excitation over inhibition is key. Glutamate is the primary excitatory neurotransmitter, and GABA is the primary inhibitory neurotransmitter. Therefore, an imbalance involving both an excess of glutamate and/or a deficiency of GABA can lead to seizures.

Weekly Pathology Exam - June 19, 2026 (Section A: MCQs)

Questions, Answers & Explanations