USMLE Step 1

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)?

• 69-420

• 120-140

• 140-150

• 50-100

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 the following?

• Normal Kidney

• Nephritis

• Nephritic Syndrome

• Pheochromocytoma

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?

• Candida albicans

• Addison's Disease

• Angina

• Aplastic Anemia

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 likely diagnosis?

• Pneumonia

• Pneumothorax

• Emphysema

• Bronchitis

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?

• Anorexia, Bipolar, Cluster C Disorder

• Bipolar, Manic with psychotic features

• Depression, Delirium, Bulimia

• Bipolar, Tourette's, Acute Pancreatitis

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?

• T-cell death

• Apoptosis of The B-cell

• Apoptosis of activated Lymph nodes

• Lymph node death

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?

• Vitamin AB

• ACE

• Vitamin B

• Vitamin A

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 condition?

• Pheochromocytoma

• Cushing Syndrome

• Multiple Endocrine Neoplasia

• Conversion of testosterone to dihydrotestosterone

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?

• Osteoperosis

• Barret's Esophagus

• ARDS

• Atheroslcerosis