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USMLE STEP3 Exam
Step3 (Page 18 )

Updated On: 15-Feb-2026
Page 18 of 162
PDF with 804 Questions

While visiting a neighbor, a 14-year-old girl is bitten on the left hand by the neighbor's pet cat. The cat is an indoor pet and has had all of the required routine vaccinations. You see the girl in the office approximately 1 hour after the injury. On the dorsum of the left hand you see two shallow puncture wounds that are not actively bleeding. She has full range of motion of her hand, normal capillary refill, and sensation. You see in the chart that the patient had a diphtheria/tetanus (dT) booster vaccine last year. What is the most appropriate management at this time?

  1. Recommend local care at home with hydrogen peroxide and topical antibiotics.
  2. Give a booster dT and start oral cephalexin.
  3. Give an intramuscular (IM) dose of penicillin and emergently refer to a hand surgeon for debridement.
  4. Irrigate the wounds and prescribe oral amoxicillin/clavulanic acid (Augmentin).
  5. Start oral ciprofloxacin and refer to the health department for rabies prophylaxis.

Answer(s): D

Explanation:

Animal bites, most commonly from pet dogs and cats, result in over 1 million wounds in the United States each year. Bites and scratches from cats are prone to infection with organisms that are normally found in the animal's oropharynx. These infections tend to be polymicrobic and include alpha- hemolytic streptococci, staphylococci, and Pasteurella species, among others. Pasteurella infections tend to spread rapidly, often within hours. Cat bites may also result in the transmission of rabies and tetanus. In the setting of a well cared for indoor house pet, rabies would be unlikely and rabies vaccine unnecessary, although reporting the injury to the health department may be required (depending on local statute). A dT booster would not be necessary, as she had one within a year. Surgical debridement would not be necessary for a shallow wound with normal hand function. If there were signs of tendon, nerve, or vascular injury, then surgical evaluation would be mandatory. Local care alone would not be appropriate because of the propensity for cat bite wounds to become infected. Antibiotic prophylaxis is recommended for most cat bite wounds, particularly those involving the hands. The recommended first-line agent is a combination of beta- lactam and beta-lactamase inhibitor, such as amoxicillin/ clavulanic acid. An alternative regimen includes clindamycin with either TMP-SMZ (Bactrim DS) or a fluoroquinolone.



A 29-year-old woman complains of fatigue and decreased exercise tolerance. She takes no medications and denies changes in the color of the stool. Physical examination is significant for pale skin and conjunctivae. Stool was negative for blood. Laboratory evaluation revealed Hgb of 7.8 g/dL, reticulocytopenia, microcytosis, and hypochromia.
The U.S. Preventive Services Task Force (USPSTF) recommends screening for iron deficiency in which of the following?

  1. asymptomatic persons over the age of 65 at risk for gastric cancer
  2. immigrants from developing countries
  3. asymptomatic infants at high risk
  4. pregnant women
  5. blood donors

Answer(s): D

Explanation:

Iron-deficiency anemia (IDA) is characterized by a low MCV, low ferritin, and a high erythrocyte protoporphyrin in serum. Microcytosis and hypochromia are the hallmark in the peripheral smear. Elevated erythrocyte protoporphyrin in serum can also be seen in anemia of chronic disease and chronic lead poisoning.
The USPSTF recommends screening pregnant women for IDA, but found insufficient evidence to recommend for or against routine screening in other asymptomatic persons. However, the guidelines did recommend routine iron supplementation in asymptomatic infants 612 months of age who are at high risk of IDA. Infants are considered to be at high risk if they are living in poverty; are Black, Native American, or Alaskan Native; are immigrants from a developing country; are preterm or low birth weight; or if their primary dietary intake is unfortified cow's milk. The most common cause of cobalamin deficiency is pernicious anemia. Rarely, hypersecretion of gastric acid (i.e., Zollinger- Ellison syndrome) results in cobalamin deficiency.
The peripheral smears in folate and cobalamin deficiency are indistinguishable, showing macrocytosis and hypersegmented neutrophils. Both methylmalonic acid and homocysteine levels become elevated with cobalamin deficiency. Folate deficiency is caused by decreased intake, increased utilization, or impaired absorption. Because body stores of folate are low, persons who have an inadequate consumption will become anemic in several months. The recommended amount of dietary folate is 400 g/day. Anemia is not a diagnosis in itself; it is an objective sign of the presence of a disease. It is always secondary to an underlying condition. In most cases, a thorough history and physical examination can help elicit the pathogenesis of the anemia and direct appropriate treatment.



A 29-year-old woman complains of fatigue and decreased exercise tolerance. She takes no medications and denies changes in the color of the stool. Physical examination is significant for pale skin and conjunctivae. Stool was negative for blood. Laboratory evaluation revealed Hgb of 7.8 g/dL, reticulocytopenia, microcytosis, and hypochromia.
In vitamin B12 or folate deficiency, which of the following statements is correct?

  1. High serum levels of homocysteine and decreased levels of methylmalonic acid are reliable indicators of cobalamin deficiency.
  2. The recommended amount of dietary folate is 800 g/day.
  3. The peripheral smear in patients with cobalamin deficiency is identical to that found in folate deficiency.
  4. The most common cause of cobalamin deficiency is hypersecretion of gastric acid (i.e., Zollinger- Ellison syndrome).
  5. Because body folate stores are high, individuals with low consumption of folate will take several years to become anemic.

Answer(s): C

Explanation:

Iron-deficiency anemia (IDA) is characterized by a low MCV, low ferritin, and a high erythrocyte protoporphyrin in serum. Microcytosis and hypochromia are the hallmark in the peripheral smear. Elevated erythrocyte protoporphyrin in serum can also be seen in anemia of chronic disease and chronic lead poisoning.
The USPSTF recommends screening pregnant women for IDA, but found insufficient evidence to recommend for or against routine screening in other asymptomatic persons. However, the guidelines did recommend routine iron supplementation in asymptomatic infants 612 months of age who are at high risk of IDA. Infants are considered to be at high risk if they are living in poverty; are Black, Native American, or Alaskan Native; are immigrants from a developing country; are preterm or low birth weight; or if their primary dietary intake is unfortified cow's milk. The most common cause of cobalamin deficiency is pernicious anemia. Rarely, hypersecretion of gastric acid (i.e., Zollinger- Ellison syndrome) results in cobalamin deficiency.
The peripheral smears in folate and cobalamin deficiency are indistinguishable, showing macrocytosis and hypersegmented neutrophils. Both methylmalonic acid and homocysteine levels become elevated with cobalamin deficiency. Folate deficiency is caused by decreased intake, increased utilization, or impaired absorption. Because body stores of folate are low, persons who have an inadequate consumption will become anemic in several months. The recommended amount of dietary folate is 400 g/day. Anemia is not a diagnosis in itself; it is an objective sign of the presence of a disease. It is always secondary to an underlying condition. In most cases, a thorough history and physical examination can help elicit the pathogenesis of the anemia and direct appropriate treatment.



A 29-year-old woman complains of fatigue and decreased exercise tolerance. She takes no medications and denies changes in the color of the stool. Physical examination is significant for pale skin and conjunctivae. Stool was negative for blood. Laboratory evaluation revealed Hgb of 7.8 g/dL, reticulocytopenia, microcytosis, and hypochromia. Which of the following is the most appropriate next step in the management of the anemia in this woman?

  1. Start iron therapy as soon as possible.
  2. Transfuse RBCs and start iron therapy.
  3. Start B12 and folate replacement.
  4. Identify the cause of the anemia with a thorough history and physical examination.
  5. Start iron therapy and B12 replacement.

Answer(s): D

Explanation:

Iron-deficiency anemia (IDA) is characterized by a low MCV, low ferritin, and a high erythrocyte protoporphyrin in serum. Microcytosis and hypochromia are the hallmark in the peripheral smear. Elevated erythrocyte protoporphyrin in serum can also be seen in anemia of chronic disease and chronic lead poisoning.
The USPSTF recommends screening pregnant women for IDA, but found insufficient evidence to recommend for or against routine screening in other asymptomatic persons. However, the guidelines did recommend routine iron supplementation in asymptomatic infants 612 months of age who are at high risk of IDA. Infants are considered to be at high risk if they are living in poverty; are Black, Native American, or Alaskan Native; are immigrants from a developing country; are preterm or low birth weight; or if their primary dietary intake is unfortified cow's milk. The most common cause of cobalamin deficiency is pernicious anemia. Rarely, hypersecretion of gastric acid (i.e., Zollinger- Ellison syndrome) results in cobalamin deficiency.
The peripheral smears in folate and cobalamin deficiency are indistinguishable, showing macrocytosis and hypersegmented neutrophils. Both methylmalonic acid and homocysteine levels become elevated with cobalamin deficiency. Folate deficiency is caused by decreased intake, increased utilization, or impaired absorption. Because body stores of folate are low, persons who have an inadequate consumption will become anemic in several months. The recommended amount of dietary folate is 400 g/day. Anemia is not a diagnosis in itself; it is an objective sign of the presence of a disease. It is always secondary to an underlying condition. In most cases, a thorough history and physical examination can help elicit the pathogenesis of the anemia and direct appropriate treatment.



A 23-year-old woman presents to your acute care clinic with a complaint of fever, sore throat, and malaise of sudden onset. Her prior medical history is significant for schizophrenia. Her vitals signs are:
BP 116/80, HR 112, RR 26, Temp 100.6 degrees Fahrenheit. On physical examination, her oral cavity features painful aphthous ulcers as well as swollen gums. Initial laboratory testing includes a CBC which returns with the following results:
· Leukocyte count 800/mm3
· Hgb 12.1 g/dL
· HCT 37.0%
· Platelet count 212 × 109/L
· Differential:
· Neutrophils, segmented 52%
· Neutrophils, bands 3%
· Lymphocytes 35%
· Monocytes 7%
· Eosinophils 3%
· Basophils 0%
Use of which of the following must be considered when formulating a differential diagnosis to explain this patient's symptoms?

  1. haloperidol
  2. chlorpromazine
  3. risperidone
  4. thioridazine
  5. clozapine

Answer(s): E

Explanation:

This patient's presentation is consistent with agranulocytosis, which is defined by an absolute neutrophil count (ANC) of fewer than 500/mm3. ANC is defined as the percentage of the WBC count that is accounted for by segmented neutrophils and bands. In the case of this patient, the ANC is 55% of the WBC count or 440/mm3. Individuals with agranulocytosis commonly experience a sudden onset of malaise, fever, chills, and pharyngitis. They may also develop painful aphthous ulcers affecting the oropharyngeal mucosa. Suppression of the bone marrow, including agranulocytosis, is associated with the use of clozapine. The incidence approaches 1% within several months of treatment, independent of dose. Patients on clozapine should be monitored closely with weekly measurement of the CBC. Mild leukocytosis and other blood dyscrasias occur much less frequently with other antipsychotic drugs.Usually, there is a prodrome of several weeks duration in which the WBC count gradually declines. Decreasing the dose or discontinuing the offending agent does not always prevent progression to full blown agranulocytosis. Patients with druginduced neutropenia recover more quickly with the assistance of granulocyte colonystimulating factor (G-CSF). Additionally, individuals suffering from agranulocytosis frequently develop infections which require the use of antibiotic therapy. In these cases, further supportive and symptomatic care may be necessary depending on the severity of infection. Delaying or withholding intervention is inappropriate. Tardive dyskinesia is an adverse effect related to use of antipsychotic medications; it is not inherently related to agranulocytosis.






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