USMLE Laboratory Values
Serum LDL-cholesterol concentrations are measured in blood samples collected from 25 healthy volunteers. The data
follow a normal distribution. The mean and standard deviation for this group are 130 mg/dL and 25 mg/dL,
respectively. The standard error of the mean is 5.0. With a 95% confidence level, the true mean for the population
from which this sample was drawn falls within which of the following ranges (in mg/dL)?
A 48-year-old man dies suddenly of a cardiac arrhythmia. Six weeks ago, he was resuscitated from a cardiac arrest
caused by coronary artery disease and developed oliguric renal failure. Five weeks ago (1 week after being
resuscitated), his serum urea nitrogen (BUN) concentration was 40 mg/dL, his serum creatinine concentration was 3.5
mg/dL, and his urine contained granular casts. Four weeks ago, his oliguria resolved, and his BUN and serum
creatinine concentrations returned to normal. Examination of his kidneys at autopsy is most likely to show which of
In a sample of 100 individuals, the mean leukocyte count is 7500/mm3, with a standard deviation of 1000/mm3. If the
leukocyte counts in this population follow a normal (gaussian) distribution, approximately 50% of individuals will
have which of the following total leukocyte counts?
A 55-year-old woman comes to the clinic because of a 2-month history of increasingly severe vaginal pain and itching
during sexual intercourse. She avoids intercourse with her husband because of the symptoms. She has been in a
monogamous relationship with her husband for the past 25 years. She has type 2 diabetes mellitus. Her vital signs are
within normal limits. Pelvic examination shows edematous and erythematous vaginal mucosa with white discharge.
A photomicrograph of a vaginal smear is shown. Which of the following is the most likely causal infectious agent?
A 39-year-old man comes to the physician because of a 6-month history of progressive shortness of breath. He has
had a cough productive of white sputum for 2 years. He smoked 1 pack of cigarettes daily for 16 years but quit 10 years
ago. He is in mild respiratory distress with pursed lips and a barrel chest; he is using the accessory muscles of
respiration. Breath sounds are distant and crackles are present in the lower lung fields bilaterally. Pulmonary function
tests show a decreased FEV1:FVC ratio, increased residual volume, and decreased diffusion capacity. An x-ray of the
chest shows hyperinflation and hypertranslucency of the lower lobes of both lungs. Which of the following is the most
A previously healthy 33-year-old woman is brought to the emergency department by the Secret Service for stalking
the president of the USA for 2 months. She claims to be married to the president’s twin brother and states that the
president just had his twin kidnapped to avoid competition. She speaks rapidly and is difficult to interrupt. Her
associations are often loose. She says, “I haven’t slept for days, but I won’t even try to sleep until my husband is
rescued. God has been instructing me to take over the White House. I can’t wait to be reunited with my husband. I
hear his voice telling me what to do.” When asked about drug use, she says she uses only natural substances. She
refuses to permit blood or urine tests, saying, “I don’t have time to wait for the results.” Which of the following is the
most likely diagnosis?
During an experiment, a mouse is vaccinated with live attenuated bacteria at two different times. The results following
immunization are shown in the graph. The subject’s serum total antibody concentration (Y-axis) was measured at
various time points (X-axis). The response to the first immunization is indicated by Peak A, while that of the second
immunization with the same bacterial antigen is indicated by Peak B. The phase of the immune response represented
by the asterisk is most likely the direct result of which of the following?
A 53-year-old man comes to the physician because of a dry scaly rash on his body for the past year. He has had a 15-
kg (33-lb) weight loss during the past year. He is 178 cm (5 ft 10 in) tall and now weighs 54 kg (120 lb); BMI is
17 kg/m2. His stools have a large volume and float. Which of the following nutrient deficiencies is most likely?
In screening for prostate cancer, the current serum prostate-specific antigen concentration at which biopsy is
recommended is 4.1 ng/mL. If the threshold for recommending a biopsy procedure were lowered to 2.0 ng/mL, which
of the following changes would occur to the positive and negative predictive values of the test?
Positive Predictive Value Negative Predictive Value
In informing a couple that their newborn has Down syndrome, there is a specific, relatively limited amount of
information that the consulting physician should give immediately. The rest can be discussed at a later time. Which
of the following best explains the purpose of using this approach to disclosure?
A 25-year-old man volunteers to participate in a study of exercise. The solid curves in the graph show the relationship
between right atrial pressure and cardiac output (cardiac function curves). The dashed lines show the relationship
between cardiac output and right atrial pressure (vascular function curves). Point X is the pre-exercise equilibrium
point. Which of the following labeled areas is the most likely new cardiac and vascular equilibrium point during
exercise in this subject?
A 62-year-old man comes to the physician because of a 6-month history of urinary hesitancy and dribbling after
urination. He has to urinate two to three times nightly. Physical examination shows a diffusely enlarged, firm, and
nontender prostate. Which of the following is most likely to have contributed to the development of this patient’s
An 18-year-old woman with sickle cell disease is brought to the emergency department by her parents because of a 2-
hour history of severe abdominal pain and nausea. Her parents say that she had a cheeseburger, milk shake, and
chocolate bar for lunch. Her temperature is 37°C (98.6°F). Physical examination shows tenderness over the right upper
quadrant of the abdomen, radiating to the right shoulder. Ultrasonography of the right upper quadrant of the abdomen
shows gallstones. Which of the following is the most likely underlying cause of this patient’s current condition?
A 45-year-old man is brought to the emergency department 30 minutes after the sudden onset of crushing chest pain.
His father, maternal aunt, and paternal uncle all died of myocardial infarctions under the age of 50 years. Physical
examination shows tendinous xanthomas on the hands and thickened Achilles tendons. Serum lipid studies show a
total cholesterol concentration of 410 mg/dL, HDL-cholesterol concentration of 30 mg/dL, and triglyceride
concentration of 140 mg/dL. The diagnosis of myocardial infarction is made. This patient most likely has a deficiency
of which of the following?
An experimental animal is created in which the germinal centers of the reactive lymph nodes show shrinkage of cells,
cytoplasmic budding, no adjacent inflammation, and intact plasma membranes. These cellular findings are most likely
caused by which of the following mechanisms?
Investigators conduct a study that evaluates the effect of finasteride on the incidence of prostate cancer in 500 patients.
The investigators recruit an additional 1000 patients for the study. Which of the following effects will this have on the
A 76-year-old man dies of a massive cerebral infarction shortly after admission to the hospital. During the past 10
years, he has had several smaller cerebral infarctions and two transient ischemic attacks. Examination of a cerebral
cortex specimen obtained at autopsy shows extensive gliosis. This finding is most likely caused by the growth and
proliferation of which of the following?
A 65-year-old woman is brought to the emergency department because of a 10-minute history of chest tightness and
severe pain of her left arm. Physical examination shows jugular venous distention. Crackles are heard over the lung
fields. An ECG shows ST-segment elevation greater than 1 mm in leads V4 through V6 and new Q waves. Serum
studies show an increased troponin I concentration. Which of the following labeled points in the graph best represents
the changes in cardiac function that occurred during the first 10 seconds after the onset of pain in this patient?
A previously healthy 52-year-old woman comes to the physician because of a 2-month history of fatigue, constipation,
and frequent urination. Her temperature is 37.1°C (98.8°F), pulse is 80/min, respirations are 14/min, and blood
pressure is 140/90 mm Hg. Diffuse crackles are heard bilaterally. Her serum calcium concentration is 11.1 mg/dL,
and serum parathyroid hormone concentration is decreased. A chest x-ray shows bilateral hilar lymphadenopathy and
interstitial infiltrates. Which of the following is the most likely cause of this patient’s hypercalcemia?
A 66-year-old man who was recently diagnosed with Parkinson disease comes to the physician for a follow-up
examination. Carbidopa-levodopa therapy was initiated at the time of diagnosis. The patient tells the physician that he
still has episodes during which he “freezes.” He has a clumsy gait, and there is rigidity of his upper extremities and
hands. An adjunct therapy designed to inhibit which of the following enzymes is most likely indicated in this patient?
A study is conducted to assess the effects of epinephrine on total peripheral resistance. An anesthetized experimental
animal is injected with a bolus of the drug in both the presence and absence of doxazosin. The results are shown in
the graph. Which of the following best represents the signal transduction pathways used by epinephrine to produce
Epinephrine Without Doxazosin Epinephrine With Doxazosin
A 46-year-old woman comes to the physician because of a 3-day history of intermittent pain with urination and
increased urinary frequency. She says that she had one similar episode during the past 6 months. She also has had
irregular menses, and her last menstrual period occurred 2 months ago. She has not had fever, nausea, vomiting, or
blood in her urine. She is sexually active with one male partner. Physical examination shows no abnormalities.
Leukocyte esterase positive
Which of the following is the strongest predisposing risk factor for the development of this patient’s condition?
A 28-year-old man comes to the physician because of a 2-month history of a rash on his wrists and hands. He is a
first-year mortuary science student. He also works on his grandfather’s farm each weekend. His hobbies include raising
homing pigeons and repairing vintage motorcycles. He recently changed to a different type of laundry detergent to
save money. Physical examination shows a diffuse erythematous rash involving both hands up to the wrist creases.
The rash does not extend over any other parts of the body. Which of the following is the most likely cause of this
A 10-year-old boy is brought to the emergency department in the middle of summer because of fever, headache, and
photophobia. Several of his camp mates have had a similar illness. Physical examination shows mild nuchal rigidity.
A lumbar puncture is performed. Laboratory studies show:
Serum glucose 90 mg/dL
Pressure, opening 5 0 mm H2O
Glucose 65 mg/dL
Total protein 70 mg/dL
Leukocyte count 43/mm3 (95% lymphocytes)
Which of the following infectious agents is the most likely cause of these findings?
A healthy 30-year-old woman participates in a study of the relationship between cardiovascular function and posture.
Placed in a room with a comfortable temperature (72°F) and humidity (40%), she moves from a standing to a supine
position. Which of the following sets of changes is most likely in the reflex control of this woman’s cardiovascular
Carotid Sinus Vagal Efferent
Baroreceptor Atrial Stretch Activity
Activity Receptor Activity to the Heart
A 31-year-old woman with a 5-year history of fatigue comes to the physician for an initial visit. She has seen four
other physicians for the same condition within the past 6 months, but no abnormalities were found. She gives the
physician a large folder that contains her medical records. She says, “I can barely get out of bed most mornings, but
nobody can figure out why because all of my tests turn out normal. I really think I have chronic fatigue syndrome.
What do you know about this condition?” The physician has not treated any patient with chronic fatigue syndrome
before. Which of the following initial statements by the physician is most appropriate to establish rapport with this
A 3-week-old girl delivered at term with no complications is brought to the physician by her mother because of a 1-
week history of yellow eyes and skin, tan-colored stools, and dark brown urine. The newborn has been breast-feeding
without difficulty. She is alert and appears to be in no distress. She is at the 50th percentile for length and weight.
Physical examination shows scleral icterus and jaundice. There is mild hepatomegaly; the spleen is not palpable.
Laboratory studies show:
Hemoglobin 14.4 g/dL
Leukocyte count 8000/mm3
Albumin 3.5 g/dL
Bilirubin, total 14 mg/dL
Direct 12.5 mg/dL
AST 50 U/L
ALT 45 U/L
Which of the following is the most likely diagnosis?
A 65-year-old woman comes to the physician for a follow-up examination after blood pressure measurements were
175/105 mm Hg and 185/110 mm Hg 1 and 3 weeks ago, respectively. She has well-controlled type 2 diabetes
mellitus. Her blood pressure now is 175/110 mm Hg. Physical examination shows no other abnormalities.
Antihypertensive therapy is started, but her blood pressure remains elevated at her next visit 3 weeks later. Laboratory
studies show increased plasma renin activity; the erythrocyte sedimentation rate and serum electrolytes are within the
reference ranges. Angiography shows a high-grade stenosis of the proximal right renal artery; the left renal artery
appears normal. Which of the following is the most likely diagnosis?
Results of a study that examined the impact of risk factors on cardiovascular health are being evaluated. In the study,
serum LDL-cholesterol (LDL) concentration is found to have a correlation of 0.6 with serum high-sensitivity Creactive
protein (hs-CRP) concentration. Which of the following statements best describes the relationship between
LDL concentration and hs-CRP concentration based on this finding?
A pharmaceutical company is developing a new bronchodilator agent. The graph shows concentration-response curves
for three investigational drugs (Drugs X, Y, and Z), describing their effect on bronchial smooth muscle relaxation.
Based on these data, which of the following best describes the relationship among these three agents?
A 72-year-old man comes to the physician for a health maintenance examination. He has no personal or family history
of major medical illnesses. He has never smoked cigarettes. Pulse oximetry on room air shows an oxygen saturation
of 98%. Physical examination shows plethoric skin and splenomegaly. Laboratory studies show:
Hemoglobin 21.1 g/dL
Leukocyte count 15,000/mm3
Segmented neutrophils 68%
Platelet count 501,000/mm3
Leukocyte alkaline phosphatase increased
A peripheral blood smear shows occasional giant platelets. The primary hematologic defect in this patient most likely
occurred in which of the following cells?
A 45-year-old man comes to the physician because of a 10-year history of heartburn that occurs after he eats late at
night or consumes spicy food. He has had no weight loss or difficulty swallowing. He takes over-the-counter antacids
as needed, but they relieve his discomfort only temporarily. Physical examination shows no abnormalities. An
endoscopy is done. The distal esophagus is shown in the photograph. Which of the following is the most likely cause
of this patient’s symptoms?
A 21-year-old man comes to the emergency department in the winter because of headache, nausea, and dizziness for
4 hours. He has not had fever, chills, or shortness of breath. He has no history of major medical illness. He lives in a
basement apartment of a three-story house. He smokes 1½ packs of cigarettes daily. Physical examination shows no
abnormalities. It is most appropriate for the physician to ask the patient for more information about which of the
following historical factors?
A 56-year-old woman comes to the physician because of a 2-year history of recurrent urinary tract infections
accompanied by left flank pain. Physical examination shows no abnormalities. Renal ultrasonography shows leftsided
hydronephrosis. A T2-weighted coronal MRI of the abdomen is shown; the arrow indicates the hydronephrosis.
The left renal collecting system is most likely obstructed at which of the following anatomic locations in this patient?
A 25-year-old woman comes to the physician because of a long history of pain with menses. The pain occurs on the
first day of her 5-day menstrual period and lasts all day. She rates the pain as 10 on a 10-point scale. The most
appropriate initial pharmacotherapy to relieve this patient’s pain has which of the following mechanisms of action?
A 35-year-old man is brought to the emergency department 30 minutes after he sustained a cut on his hand while
loading cargo at his job. He lives alone and takes most of his meals at a local restaurant. He eats mostly snack foods
at the bar and fast food. He drinks four to six 12-oz beers daily and double that amount on weekends. He takes no
medications. Physical examination shows a 3-cm laceration on the right hand that is bleeding steadily. Laboratory
studies show a hemoglobin concentration of 11 g/dL, leukocyte count of 4000/mm3, and platelet count of
150,000/mm3. A photomicrograph of a peripheral blood smear is shown. A deficiency of which of the following is the
most likely cause of this patient’s anemia?
A 3800-g (8-lb 6-oz) newborn is delivered vaginally at 39 weeks’ gestation after an uncomplicated pregnancy. Apgar
scores are 9 and 9 at 1 and 5 minutes, respectively. The newborn is crying, has pink skin, and appears vigorous.
Physical examination shows a vagina and also a structure that appears to be a penis, with the urethra located at the
base near the opening of the vagina. Chromosomal analysis is ordered. Which of the following is the most likely cause
of the intersex findings in this newborn if the karyotype is found to be 46,XX?
A 65-year-old man is admitted to the hospital because of a 12-hour history of chest pain. Physical examination shows
no abnormalities. Serum studies show an increased troponin I concentration. The diagnosis of myocardial infarction
is made. It is suspected that this patient’s condition deteriorated as a result of ischemia-reperfusion injury. The
increased serum troponin I concentration in this patient most likely occurred as a result of which of the following
A randomized clinical trial is conducted to compare wound healing and cosmetic differences between two surgical
procedures for closing skin wounds following cesarean delivery. A total of 1000 women undergoing cesarean delivery
during a 6-month period are enrolled in the study, which was 85% of the total number of patients undergoing the
procedure. The results show a wound infection rate of 12 cases per 1000 women for Procedure A and 18 cases per
1000 women for Procedure B. Which of the following is the best estimate of the absolute risk reduction for wound
infection following Procedure A compared with Procedure B?
A 22-year-old man is brought to the emergency department 15 minutes after diving off a pier into shallow water,
striking his forehead on the bottom of the pond. He says that he felt immediate pain in his neck and then lost all ability
to move or feel his legs. Physical examination shows that all muscle function above the level of the injury is preserved.
A lateral x-ray of the cervical spine is shown. Which of the following functions is most likely spared in this patient?