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ABPath Clinical Pathology study materials
ABPath Clinical Pathology study resources

ABPath Clinical Pathology practice questions

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Question 1Clinical Chemistry

A serum sample left on the clot at room temperature overnight is most likely to show which of the following changes compared with a promptly separated sample?

  1. Decreased glucose and decreased potassium
  2. Increased glucose and increased potassium
  3. Increased glucose and decreased potassium
  4. Decreased glucose and increased potassium Correct answer.

Explanation

Cells continue glycolysis after collection, lowering glucose, and leak intracellular potassium into serum, raising potassium. Prompt separation of serum or plasma prevents these artifacts.

Question 2Clinical Chemistry

Which specimen type is preferred for measuring ionized calcium?

  1. Heparinized whole blood or plasma Correct answer.
  2. EDTA plasma
  3. Serum from a plain red-top tube
  4. Citrated plasma

Explanation

Ionized calcium must be measured in anaerobically handled heparinized whole blood or plasma because calcium chelators and clot contact alter results. EDTA and citrate bind calcium and falsely lower ionized calcium.

Question 3Clinical Chemistry

The reference method for measuring serum glucose is based on which principle?

  1. Copper reduction with phosphomolybdate
  2. Nitroblue tetrazolium reduction
  3. Hexokinase enzymatic phosphorylation Correct answer.
  4. Alkaline picrate reaction

Explanation

The hexokinase method is the reference procedure for glucose because it is highly specific for glucose. Other methods such as glucose oxidase or copper reduction are less specific or subject to interference.

Question 4Clinical Chemistry

A patient with a fasting glucose of 118 mg/dL and a 2-hour OGTT value of 165 mg/dL is best classified as having which condition?

  1. Impaired glucose tolerance Correct answer.
  2. Diabetes mellitus
  3. Normal glucose tolerance
  4. Impaired fasting glucose only

Explanation

A 2-hour OGTT value of 140 to 199 mg/dL defines impaired glucose tolerance. The fasting value of 118 mg/dL falls in the impaired fasting glucose range of 100 to 125 mg/dL.

Question 5Clinical Chemistry

Hemoglobin A1c reflects average glycemia over approximately which period?

  1. 6 to 12 months
  2. 2 to 4 weeks
  3. 2 to 3 months Correct answer.
  4. 1 to 2 weeks

Explanation

A1c reflects mean glucose over the lifespan of the red cell, roughly 2 to 3 months. Shorter intervals reflect only recent changes in glycemia.

Question 6Clinical Chemistry

In a patient with a hemoglobin variant that shortens red cell survival, the measured hemoglobin A1c is most likely to be which of the following?

  1. Falsely elevated
  2. Unaffected
  3. Falsely decreased Correct answer.
  4. Immeasurable

Explanation

Shortened red cell survival reduces the time available for glycation, falsely lowering A1c. Alternative markers such as fructosamine or glycated albumin may be used.

Question 7Clinical Chemistry

Which analyte is the most sensitive marker of acute myocardial infarction when measured 3 to 6 hours after symptom onset?

  1. Myoglobin Correct answer.
  2. Troponin I
  3. Lactate dehydrogenase
  4. Creatine kinase MB

Explanation

Myoglobin rises earliest after myocardial injury, within 2 to 3 hours, making it sensitive though nonspecific. Troponin is more specific but rises slightly later.

Question 8Clinical Chemistry

A patient presents 4 days after chest pain. Which cardiac marker is most useful for detecting the recent infarction at this time?

  1. AST
  2. Troponin I Correct answer.
  3. Myoglobin
  4. CK-MB

Explanation

Troponin remains elevated for 7 to 14 days, making it useful for late presentation. Myoglobin and CK-MB normalize earlier.

Question 9Clinical Chemistry

Which fraction of alkaline phosphatase is elevated in Paget disease of bone?

  1. Intestinal fraction
  2. Placental fraction
  3. Liver fraction
  4. Bone fraction Correct answer.

Explanation

Paget disease increases osteoblastic activity, raising the bone-specific alkaline phosphatase fraction. Liver, placental, and intestinal fractions rise in other conditions.

Question 10Clinical Chemistry

A 55-year-old man has a total calcium of 9.0 mg/dL and an albumin of 2.0 g/dL. What is the albumin-corrected calcium?

  1. 11.4 mg/dL
  2. 9.0 mg/dL
  3. 9.8 mg/dL
  4. 10.6 mg/dL Correct answer.

Explanation

The correction adds 0.8 mg/dL to total calcium for each 1 g/dL that albumin is below 4.0. Here the deficit is 2 g/dL, adding 1.6 mg/dL to yield 10.6 mg/dL.

Question 11Clinical Chemistry

Which laboratory finding is characteristic of primary hyperparathyroidism?

  1. High calcium with low phosphate Correct answer.
  2. Low calcium with low phosphate
  3. Low calcium with high phosphate
  4. High calcium with high phosphate

Explanation

Parathyroid hormone raises serum calcium by bone resorption and renal reabsorption while increasing phosphate excretion, producing high calcium with low phosphate.

Question 12Clinical Chemistry

Which condition produces a normal anion gap metabolic acidosis?

  1. Diarrhea Correct answer.
  2. Lactic acidosis
  3. Salicylate poisoning
  4. Diabetic ketoacidosis

Explanation

Diarrhea causes bicarbonate loss with renal retention of chloride, producing a hyperchloremic normal anion gap acidosis. Ketoacidosis, lactic acidosis, and salicylate toxicity are high anion gap acidoses.

Question 13Clinical Chemistry

A patient has a pH of 7.50, a PaCO2 of 30 mmHg, and a bicarbonate of 24 mEq/L. Which acid-base disorder is present?

  1. Metabolic alkalosis
  2. Respiratory acidosis
  3. Metabolic acidosis
  4. Respiratory alkalosis Correct answer.

Explanation

An elevated pH with a low PaCO2 and normal bicarbonate indicates respiratory alkalosis. The low CO2 reflects hyperventilation.

Question 14Clinical Chemistry

Which is the most common cause of a falsely elevated serum creatinine when measured by the Jaffe reaction?

  1. High bilirubin
  2. Hyperglycemia
  3. Presence of ketones Correct answer.
  4. High protein intake

Explanation

The Jaffe reaction is nonspecific and ketones, including acetoacetate and acetone, cross-react and falsely raise creatinine. Enzymatic methods are less susceptible to this interference.

Question 15Clinical Chemistry

A 24-hour urine creatinine clearance is calculated. Which factor most limits its accuracy?

  1. Dietary sodium intake
  2. Incomplete urine collection Correct answer.
  3. Diurnal variation in creatinine
  4. Serum creatinine assay precision

Explanation

Clearance depends on a complete timed urine collection; incomplete collection underestimates clearance. Diurnal variation and assay precision have smaller effects.

Question 16Clinical Chemistry

Which formula estimates glomerular filtration rate from serum creatinine, age, and sex in adults?

  1. Henderson-Hasselbalch equation
  2. Cockcroft-Gault equation
  3. Friedewald equation
  4. MDRD or CKD-EPI equation Correct answer.

Explanation

The MDRD and CKD-EPI equations estimate GFR from creatinine, age, and sex. Cockcroft-Gault estimates creatinine clearance, while the other equations serve different purposes.

Question 17Clinical Chemistry

A patient has a serum total protein of 8.0 g/dL and an albumin of 2.5 g/dL. What is the calculated globulin?

  1. 10.5 g/dL
  2. 5.5 g/dL Correct answer.
  3. 8.0 g/dL
  4. 2.5 g/dL

Explanation

Globulin is calculated by subtracting albumin from total protein, giving 8.0 minus 2.5, or 5.5 g/dL. This derived value helps assess the globulin fraction.

Question 18Clinical Chemistry

A monoclonal spike on serum protein electrophoresis is best confirmed and quantified by which technique?

  1. Nephelometric total protein
  2. Coombs testing
  3. Immunofixation electrophoresis Correct answer.
  4. Serum osmolality

Explanation

Immunofixation electrophoresis identifies the heavy and light chain type of a monoclonal protein. Quantification is often performed by densitometry or serum free light chain assays.

Question 19Clinical Chemistry

Which lipoprotein abnormality is characterized by a deficiency of LDL receptors?

  1. Familial chylomicronemia
  2. Familial hypercholesterolemia Correct answer.
  3. Abetalipoproteinemia
  4. Tangier disease

Explanation

Familial hypercholesterolemia results from defective LDL receptors, causing markedly elevated LDL cholesterol. Other disorders involve different lipoprotein defects.

Question 20Clinical Chemistry

Using the Friedewald formula, what is the LDL cholesterol for a patient with total cholesterol 220 mg/dL, HDL 50 mg/dL, and triglycerides 150 mg/dL?

  1. 150 mg/dL
  2. 120 mg/dL
  3. 170 mg/dL
  4. 140 mg/dL Correct answer.

Explanation

The Friedewald formula is LDL equals total cholesterol minus HDL minus triglycerides divided by 5. Here 220 minus 50 minus 30 equals 140 mg/dL.

Question 21Clinical Chemistry

Which enzyme is most specific for hepatocellular injury?

  1. Amylase
  2. Alanine aminotransferase Correct answer.
  3. Gamma-glutamyl transferase
  4. Alkaline phosphatase

Explanation

ALT is relatively specific for hepatocytes, with higher concentrations in liver than in other tissues. Alkaline phosphatase and GGT are more associated with cholestasis.

Question 22Clinical Chemistry

A patient with a history of alcohol use has an AST to ALT ratio greater than 2. This pattern is most consistent with which condition?

  1. Acetaminophen toxicity
  2. Viral hepatitis
  3. Biliary obstruction
  4. Alcoholic hepatitis Correct answer.

Explanation

Alcoholic hepatitis characteristically produces an AST to ALT ratio above 2, partly due to pyridoxine deficiency reducing ALT synthesis. Viral hepatitis and acetaminophen toxicity typically show ALT greater than AST.

Question 23Clinical Chemistry

Which laboratory finding best distinguishes primary from secondary adrenal insufficiency?

  1. Serum potassium level
  2. Serum cortisol level
  3. Plasma ACTH level Correct answer.
  4. Serum sodium level

Explanation

Primary adrenal insufficiency shows elevated ACTH from loss of cortisol feedback, while secondary insufficiency shows low or inappropriately normal ACTH. Cortisol and electrolytes are abnormal in both.

Question 24Clinical Chemistry

A patient with suspected pheochromocytoma has markedly elevated plasma free metanephrines. Which preanalytical factor can falsely elevate these results?

  1. Supine position during collection
  2. Fasting before collection
  3. Acetaminophen use Correct answer.
  4. Recent carbohydrate meal

Explanation

Acetaminophen and other sympathomimetic drugs can interfere with metanephrine assays. Supine sampling and standardized conditions reduce false positives.

Question 25Clinical Chemistry

Which analyte is used to monitor compliance and absorption in patients taking levothyroxine?

  1. Thyroid peroxidase antibody
  2. Thyroid-stimulating hormone Correct answer.
  3. Total T4
  4. Thyroglobulin

Explanation

TSH is the preferred monitoring test because it reflects pituitary feedback to thyroid hormone levels. Antibodies and thyroglobulin serve other diagnostic purposes.

Question 26Clinical Chemistry

A patient has a serum osmolality of 295 mOsm/kg and a calculated osmolality of 275 mOsm/kg. What is the most likely explanation for this difference?

  1. Presence of an unmeasured osmole such as ethanol Correct answer.
  2. Laboratory error in the sodium measurement
  3. Hyperglycemia
  4. Hypernatremia

Explanation

The osmolal gap is the difference between measured and calculated osmolality. An increased gap suggests the presence of unmeasured osmoles such as ethanol, methanol, or ethylene glycol. Hyperglycemia and hypernatremia would be included in the calculated osmolality and would not cause a gap.

Question 27Clinical Chemistry

Which analyte is most appropriate to measure to assess glycemic control over the preceding 2 to 3 weeks?

  1. Glycated albumin
  2. Fructosamine Correct answer.
  3. 1,5-anhydroglucitol
  4. Hemoglobin A1c

Explanation

Fructosamine reflects glycation of serum proteins, primarily albumin, which have a half-life of about 2 to 3 weeks. Hemoglobin A1c reflects average glycemia over 2 to 3 months. Glycated albumin and 1,5-anhydroglucitol are less commonly used and reflect different time windows.

Question 28Clinical Chemistry

A patient with CKD has an eGFR of 28 mL/min/1.73 m² and a serum phosphate of 5.8 mg/dL. Which hormone is most likely elevated as a compensatory response?

  1. Calcitonin
  2. Insulin-like growth factor 1
  3. 25-hydroxyvitamin D
  4. Fibroblast growth factor 23 Correct answer.

Explanation

FGF23 is secreted by osteocytes in response to hyperphosphatemia and increases renal phosphate excretion while reducing 1,25-dihydroxyvitamin D. It rises early in CKD. 25-hydroxyvitamin D is the storage form and is not the primary phosphaturic hormone.

Question 29Clinical Chemistry

A patient with a suspected monoclonal gammopathy has a serum protein electrophoresis showing a small M-spike. Which test is most appropriate to confirm and quantify the monoclonal protein?

  1. Urine protein electrophoresis
  2. Serum immunofixation electrophoresis Correct answer.
  3. Serum free light chain ratio
  4. Quantitative immunoglobulins

Explanation

Immunofixation electrophoresis identifies the heavy- and light-chain type of the monoclonal protein, confirming its clonality. It is the standard confirmatory test after an M-spike is seen on electrophoresis. Quantification is typically done by densitometry or nephelometry.

Question 30Clinical Chemistry

A patient has a plasma osmolality of 270 mOsm/kg, a urine osmolality of 600 mOsm/kg, and a urine sodium of 40 mEq/L. What is the most likely cause of hyponatremia?

  1. Adrenal insufficiency
  2. Primary polydipsia
  3. Diuretic use
  4. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) Correct answer.

Explanation

SIADH causes euvolemic hyponatremia with inappropriately concentrated urine (urine osmolality >100 mOsm/kg) and urine sodium >40 mEq/L due to volume expansion. Primary polydipsia would produce dilute urine. Diuretics and adrenal insufficiency typically cause hypovolemia with different urine indices.

Question 31Clinical Chemistry

A patient with severe abdominal pain has a serum lipase of 950 U/L (reference <60) and a serum amylase of 120 U/L (reference <100). Which statement best explains the discordance?

  1. Lipase elevation is not diagnostically useful without concurrent amylase elevation.
  2. Amylase is more sensitive for acute pancreatitis than lipase.
  3. Lipase is more specific for pancreatic disease and remains elevated longer than amylase. Correct answer.
  4. The amylase result suggests a non-pancreatic source of abdominal pain.

Explanation

Lipase is more specific to the pancreas and has a longer half-life, so it remains elevated longer than amylase. In acute pancreatitis, lipase is often elevated more markedly and for a longer duration. Amylase can be elevated in other conditions and may normalize faster.

Question 32Clinical Chemistry

Which laboratory finding is most consistent with nephrogenic diabetes insipidus?

  1. Low urine osmolality that does not increase after desmopressin administration Correct answer.
  2. Low urine osmolality that increases after desmopressin administration
  3. High urine osmolality that decreases after desmopressin administration
  4. High urine osmolality with low serum osmolality

Explanation

In nephrogenic diabetes insipidus, the kidneys do not respond to ADH, so urine remains dilute and does not concentrate after desmopressin. In central diabetes insipidus, desmopressin increases urine osmolality. High urine osmolality is not characteristic of diabetes insipidus.

Question 33Clinical Chemistry

A patient with a known history of alcohol use disorder has a serum osmolal gap of 45 mOsm/kg. Which additional test is most useful to identify the responsible osmole?

  1. Serum ethanol concentration Correct answer.
  2. Serum creatinine concentration
  3. Serum lactate concentration
  4. Serum ketone concentration

Explanation

An elevated osmolal gap in this context suggests the presence of an unmeasured alcohol such as ethanol, methanol, or ethylene glycol. Measuring serum ethanol is the first step to identify the osmole. Lactate, ketones, and creatinine do not typically cause a large osmolal gap.

Question 34Clinical Chemistry

A patient with a TSH of 0.05 mIU/L and a free T4 of 2.8 ng/dL is suspected of factitious thyrotoxicosis. Which laboratory finding would best support this diagnosis?

  1. Low thyroglobulin level Correct answer.
  2. Elevated thyroid-stimulating immunoglobulin
  3. Elevated thyroid peroxidase antibody
  4. Elevated thyroglobulin level

Explanation

In factitious thyrotoxicosis due to exogenous thyroid hormone, endogenous thyroid hormone production is suppressed, leading to low thyroglobulin. In Graves disease, thyroglobulin is typically elevated. Thyroid antibodies are not specific for factitious disease.

Question 35Hematology

Which laboratory finding best distinguishes iron deficiency anemia from anemia of chronic inflammation when both show a low serum iron?

  1. Elevated serum ferritin
  2. Low serum ferritin
  3. Normal bone marrow iron stores
  4. Elevated total iron-binding capacity Correct answer.

Explanation

In iron deficiency, total iron-binding capacity rises as transferrin increases, whereas in anemia of chronic inflammation transferrin is reduced, giving a low TIBC. Ferritin is low in iron deficiency and normal-to-high in inflammation, so it does not behave as a shared low-iron feature.

Question 36Hematology

A peripheral smear shows microcytic hypochromic red cells with target cells and basophilic stippling, and hemoglobin electrophoresis reveals an elevated HbA2. What is the most likely diagnosis?

  1. Beta thalassemia trait Correct answer.
  2. Sideroblastic anemia
  3. Lead poisoning
  4. Alpha thalassemia trait

Explanation

Beta thalassemia trait produces microcytosis with an elevated HbA2 (and often elevated HbF), reflecting increased delta-globin chain pairing. Alpha thalassemia trait shows a normal HbA2, and lead poisoning produces stippling without a hemoglobinopathy pattern.

Question 37Hematology

Which morphologic feature on the peripheral blood smear is most characteristic of hereditary spherocytosis?

  1. Schistocytes with helmet cells
  2. Basophilic stippling of red cells
  3. Bite cells and blister cells
  4. Spherocytes with loss of central pallor Correct answer.

Explanation

Hereditary spherocytosis results from membrane skeleton defects that cause loss of membrane and a rounded cell lacking central pallor. Schistocytes suggest mechanical fragmentation, and bite cells suggest oxidative hemolysis.

Question 38Hematology

A patient with a hemolytic anemia has a positive direct antiglobulin test that reacts with anti-IgG but not anti-C3. This pattern is most consistent with which mechanism?

  1. Warm autoimmune hemolysis Correct answer.
  2. Microangiopathic hemolysis
  3. Cold agglutinin disease
  4. Paroxysmal nocturnal hemoglobinuria

Explanation

Warm autoantibodies are typically IgG that coat red cells and are detected by anti-IgG in the direct antiglobulin test. Cold agglutinins are usually IgM that fix complement, giving a C3-predominant pattern.

Question 39Hematology

The osmotic fragility test is increased in which condition?

  1. Iron deficiency anemia
  2. Thalassemia minor
  3. Sickle cell anemia
  4. Hereditary spherocytosis Correct answer.

Explanation

Spherocytes have reduced surface-to-volume ratio and lyse in hypotonic saline at higher concentrations, giving increased osmotic fragility. Cells with target shapes, such as in thalassemia and iron deficiency, tend to resist lysis.

Question 40Hematology

How is the diagnosis of paroxysmal nocturnal hemoglobinuria best confirmed by flow cytometry?

  1. Loss of CD55 and CD59 on red cells and granulocytes Correct answer.
  2. Increased CD64 expression on neutrophils
  3. Reduced CD34-positive stem cell count
  4. Presence of JAK2 V617F in myeloid cells

Explanation

Paroxysmal nocturnal hemoglobinuria arises from a PIGA mutation causing loss of GPI-anchored complement regulators CD55 and CD59. Flow cytometry demonstrating deficiency of these antigens on multiple lineages is diagnostic.

Question 41Hematology

Which red cell inclusion is seen in G6PD deficiency after an oxidative challenge?

  1. Heinz bodies Correct answer.
  2. Pappenheimer bodies
  3. Cabot rings
  4. Howell-Jolly bodies

Explanation

Oxidant stress in G6PD deficiency denatures hemoglobin into Heinz bodies, which are removed by macrophages, leaving bite cells. Howell-Jolly bodies are nuclear remnants seen after splenectomy.

Question 42Hematology

A 30-year-old woman has pancytopenia, a hypocellular bone marrow, and no hepatosplenomegaly. Which diagnosis is most likely?

  1. Myelofibrosis
  2. Aplastic anemia Correct answer.
  3. Chronic lymphocytic leukemia
  4. Acute myeloid leukemia

Explanation

Aplastic anemia presents with pancytopenia and a fatty, hypocellular marrow without splenomegaly. Myelofibrosis and leukemia typically produce a hypercellular or infiltrated marrow.

Question 43Hematology

Which finding is most characteristic of the blood picture in megaloblastic anemia?

  1. Normocytic cells with schistocytes
  2. Macro-ovalocytes with hypersegmented neutrophils Correct answer.
  3. Microcytes with pencil cells
  4. Hypochromic cells with target cells

Explanation

Impaired DNA synthesis in vitamin B12 or folate deficiency produces macro-ovalocytes and hypersegmented neutrophils, reflecting asynchronous nuclear and cytoplasmic maturation. Microcytosis is a feature of iron deficiency and thalassemia.

Question 44Hematology

A patient with severe vitamin B12 deficiency develops symmetric numbness and gait ataxia. Which structure is primarily affected?

  1. Anterior horn cells
  2. Cerebellar Purkinje cells
  3. Dorsal columns and corticospinal tracts Correct answer.
  4. Peripheral motor neurons

Explanation

Vitamin B12 deficiency causes subacute combined degeneration affecting the dorsal columns and lateral corticospinal tracts. This produces loss of position and vibration sense with upper motor neuron signs.

Question 45Hematology

Which parameter on an automated analyzer most directly reflects red cell size?

  1. Mean corpuscular hemoglobin concentration
  2. Reticulocyte hemoglobin content
  3. Red cell distribution width
  4. Mean corpuscular volume Correct answer.

Explanation

The mean corpuscular volume is the average red cell volume and defines microcytic, normocytic, and macrocytic categories. MCHC reflects hemoglobin concentration and RDW reflects size variation.

Question 46Hematology

An elevated reticulocyte count with a high reticulocyte production index in an anemic patient indicates which mechanism?

  1. Increased red cell destruction or blood loss with marrow response Correct answer.
  2. Ineffective erythropoiesis
  3. Decreased red cell production
  4. Marrow aplasia

Explanation

A high corrected reticulocyte count and production index indicate the marrow is responding appropriately to peripheral loss or destruction. Low counts in anemia suggest a production defect.

Question 47Hematology

Which coagulation abnormality is most characteristic of disseminated intravascular coagulation?

  1. Isolated prolonged aPTT with normal platelets
  2. Prolonged PT and aPTT with low fibrinogen and elevated D-dimer Correct answer.
  3. Prolonged thrombin time corrected by protamine
  4. Prolonged bleeding time with normal fibrinogen

Explanation

Disseminated intravascular coagulation consumes clotting factors and fibrinogen while generating fibrin degradation products, prolonging PT and aPTT and elevating D-dimer. Platelets are typically low.

Question 48Hematology

A mixing study is performed on a prolonged aPTT. The aPTT corrects immediately after mixing with normal plasma but prolongs again after incubation at 37°C. What does this suggest?

  1. Factor VIII deficiency
  2. A time-dependent factor inhibitor Correct answer.
  3. Heparin contamination
  4. Lupus anticoagulant

Explanation

Immediate correction followed by prolongation on incubation indicates a time- and temperature-dependent inhibitor, classically an acquired factor VIII inhibitor. A simple factor deficiency corrects and stays corrected.

Question 49Hematology

Which laboratory pattern fits von Willebrand disease type 1?

  1. Normal von Willebrand factor antigen with low ristocetin cofactor
  2. Low von Willebrand factor antigen and low ristocetin cofactor with normal multimer pattern Correct answer.
  3. Absent high-molecular-weight multimers
  4. Normal platelet count with prolonged PT

Explanation

Type 1 von Willebrand disease is a quantitative partial deficiency with proportionally low antigen and activity and a normal multimer distribution. Loss of high-molecular-weight multimers characterizes type 2A.

Question 50Hematology

A patient with a prolonged PT that corrects with normal plasma and normalizes with vitamin K administration most likely has which condition?

  1. Factor V Leiden
  2. Immune thrombocytopenia
  3. Hemophilia A
  4. Vitamin K deficiency Correct answer.

Explanation

Vitamin K deficiency reduces functional factors II, VII, IX, and X, prolonging the PT, and corrects with vitamin K repletion. Hemophilia A affects factor VIII and prolongs only the aPTT.