A hospital laboratory is comparing two methods for measuring serum sodium concentrations. Using method I, the coefficient of variation for the analysis of a series of known samples is 3.5%. Using method II, the coefficient of variation is 2.5% using the same samples. Which of the following best describes the precision of these methods?

A 25-year-old man comes to the physician because of a 2-month history of recurrent episodes of chest pain and shortness of breath. He has a 2-year history of nodules on his hands and feet. Physical examination shows numerous 1- to 2-cm yellow nodules that are palpable on both Achilles tendons and on the extensor tendons of the hands. Ophthalmologic examination shows corneal arcus. Serum studies show:

An ECG shows no abnormalities. This patient most likely has an impairment in function involving which of the following structures?

A 1-year-old girl is brought to the physician by her mother because of a 1-day history of blisters on her skin. The mother says that she has had several previous similar episodes earlier in the summer. Physical examination shows areas of dense freckling over sun-exposed areas, with hypo- and hyperpigmented macules. The skin appears dry and atrophic. This patient’s disorder is most likely caused by a defect in which of the following DNA repair mechanisms?

Patients who have recurrent infections involving Neisseria species are most likely to have a genetic deficiency in which of the following serum factors?

A 35-year-old woman is brought to the emergency department because of a 3-hour history of sharp cramping pain in the right flank. Urinalysis shows blood. A noncontrast CT scan is obtained, and a renal calculus is found to be lodged in the ureter just above the sacroiliac joint. At this point, the ureter narrows as it passes over which of the following structures?

A 22-year-old woman is admitted to the hospital because of a 10-day history of polydipsia and polyuria. She says that the urge to urinate often awakens her at night. She has been taking lithium carbonate for 2 years for bipolar disorder; her dosage was increased 6 months ago because of recurrent severe manic episodes. Her vital signs are within normal limits. Physical examination shows no abnormalities. Over the next 24 hours, urine excretion totals 6.5 L. Laboratory studies at this time show a serum sodium concentration of 148 mEq/L, serum osmolality of 315 mOsmol/kg, and urine osmolality of 75 mOsmol/kg. After administration of desmopressin, urine output and osmolality do not change. Which of the following findings in the nephron best describes the tubular osmolality, compared with serum, in this patient?

Which of the following curves shows the highest cooperativity between a hormone and its receptor?

A 79-year-old woman comes to the physician because of swollen, painful joints in her hands and knees for 6 months. Her hematocrit is 39%. Serum protein electrophoresis shows a monoclonal IgG spike of 1.8 g; serum IgA and IgM concentrations are within the reference range. Her urine does not contain Bence Jones protein. A bone marrow biopsy specimen shows no abnormalities. Which of the following is the most likely explanation for the increased serum IgG concentration in this patient?

A 17-year-old boy is brought to the emergency department because of a 2-day history of fever and shortness of breath. He underwent bone marrow transplantation for acute myelogenous leukemia 2 months ago. His temperature is 39°C (102.2°F), and respirations are 32/min. Diffuse crackles are heard over the lung fields on auscultation. A chest x- ray shows interstitial pneumonia. A photomicrograph of a biopsy specimen of the lung tissue is shown. Decreased function of which of the following most likely predisposed this patient to infection?

A 58-year-old woman with type 2 diabetes mellitus is brought to the emergency department because of an 18-hour history of fever, confusion, and pain of her left leg. Her temperature is 39.6°C (103.3°F), pulse is 124/min, respirations are 22/min, and blood pressure is 94/60 mm Hg. Physical examination shows a diffuse, erythematous rash and conjunctival injection. Erythema and edema extend from the dorsum of the left foot to the knee. She is oriented to person but not to place or time. Neurologic examination shows no other abnormalities. Serum studies show:

One day later, blood cultures grow gram-positive cocci in chains. These bacteria most likely produced a toxin that caused this patient’s condition via which of the following mechanisms?

A 25-year-old man comes to the emergency department 5 hours after developing shortness of breath and chest pain during exercise; he has had no cough or bloody mucus. He has asthma and major depressive disorder.

Current medications include fluticasone inhaler and albuterol. His temperature is 37.1°C (98.8°F), pulse is 110/min, respirations are 30/min, and blood pressure is 90/60 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 93%. Cardiac examination shows a normal S1 and S2with no murmurs and no increase in jugular venous pressure. Laboratory studies show:

A chest x-ray is shown. Which of the following pulmonary findings are most likely in this patient?

An inexpensive screening test for a disease is available through analysis of venous blood. The receiver operating characteristic (ROC) curve for five different cut points is shown. The disease is irreversible and fatal if not discovered and treated early. Which of the following is the most appropriate cut point between normal and abnormal venous blood analysis results for this screening test?

A 29-year-old woman with major depressive disorder develops constipation and urinary retention 1 week after beginning antidepressant therapy. The most likely cause of these adverse effects is blockade of which of the following neurotransmitters by the antidepressant?

A 20-year-old man with intellectual disability is brought to the physician for a routine examination. Physical examination shows a long face, prominent ears, and large testes. His younger brother and a maternal uncle have similar features. Analysis of the patient’s DNA shows 800 CGG repeated sequences (N<60) in the 5′ untranslated region of the FMR1 gene. This region of expanded CGG trinucleotide repeats is heavily methylated. Which of the following is the most likely effect of these expanded nucleotide repeats on transcription of FMR1 mRNA?

A 35-year-old woman comes to the physician for advice on smoking cessation. She has smoked 2 packs of cigarettes daily for 15 years. She has tried to quit smoking numerous times in the past without success. The physician plans to prescribe a medication that decreases the craving for cigarettes and also blocks the central nervous system stimulation caused by smoking. This drug most likely has which of the following nicotinic effects?

A 6-year-old girl of Mediterranean ancestry has severe anemia. Analysis shows normal production of a-globin gene mRNA. Production of β-globin gene mRNA is decreased 75% because of a splice-site mutation within both of the patient’s β-globin genes. Which of the following is the most likely explanation for the anemia?

A 45-year-old woman is brought to the emergency department because of the sudden onset of severe abdominal pain. Examination shows an irregularly irregular pulse, a grade 3/6, apical diastolic murmur, and an opening snap. An x-ray of the abdomen shows distention of the small intestine, the ascending colon, and a portion of the transverse colon. Which of the following is the most likely underlying cause of these findings?

An experiment is performed in which an isolated segment of skeletal muscle undergoes isotonic contraction. Which of the following would determine the maximum rate of shortening?

A newborn born with ambiguous external genitalia becomes severely dehydrated shortly after birth. Serum sodium and chloride concentrations are decreased, and serum potassium concentration is increased. The newborn’s karyotype is 46,XX. The most likely cause of these findings is a genetic defect in which of the following labeled enzymes?

A 72-year-old man with severe congestive heart failure is brought to the emergency department because of a 5-day history of malaise and vomiting. He takes no medications. His pulse is 104/min, respirations are 35/min, and blood pressure is 90/64 mm Hg. Physical examination shows dusky-colored skin, peripheral cyanosis, and 10-cm jugular venous distention. Crackles are heard over the lung bases bilaterally. Cardiac examination shows an S3. There is 2+ pitting edema to the knees bilaterally. Laboratory studies show:

Which of the following is the most likely cause of the anion gap in this patient?

A 50-year-old man with schizophrenia is admitted to the hospital because of chest pain. He develops acute fever, lethargy, and muscular rigidity 5 days later. He has been receiving haloperidol treatment since admission. His temperature is 41°C (105.8°F), pulse is 120/min, and blood pressure is 140/80 mm Hg. He is disoriented and agitated and has diffusely increased muscle tone. Serum creatine kinase activity is 1500 U/L. Which of the following is the most likely diagnosis?

A 35-year-old man comes to the physician because of a 2-week history of daily left-sided headaches that last 30 to 60 minutes. The headaches usually occur at night and often awaken him. They are accompanied by redness and tearing of the left eye and nasal congestion on the left. Alcohol seems to trigger their occurrence. Vital signs are normal. Neurologic examination shows no abnormalities. Which of the following is the most likely diagnosis?

Following a stroke, a 68-year-old man has a language problem. His speech is fluent but contains many grammatical errors, word substitutions, and neologisms. He is unable to repeat words after the examiner and is apparently unable to comprehend other verbal requests. Which of the following labeled sites on the photograph of the left hemisphere is most likely to be damaged?

For aerobic catabolism of compounds with equivalent numbers of carbon atoms, the greatest amount of energy in the form of ATP is obtained from compounds with the largest number of which of the following?

A 17-year-old girl with type 1 diabetes mellitus comes to the physician for a follow-up examination. She has had multiple admissions to the hospital during the past 5 months for diabetic ketoacidosis. She appears well. Physical examination shows no abnormalities. Laboratory studies show a hemoglobin A1c of 11.5%. She tells the physician that she does not take her insulin regularly because she either forgets to or is too busy. Which of the following is the most appropriate initial step by the physician?

A 21-year-old man comes to the physician because of intermittent episodes of light brown urine during the past year associated with upper respiratory tract infections. His blood pressure is 145/85 mm Hg. Physical examination shows no other abnormalities. Urinalysis shows microscopic blood, 3+ protein, and several RBC casts. Immunohistochemical staining of a renal biopsy specimen is most likely to show granular deposits in the glomerular mesangium predominantly consisting of which of the following immunoglobulins?

A male newborn develops vomiting and convulsions 4 hours after delivery. There is slight bulging of the fontanelles. Which of the following organisms is most likely responsible for these findings?

A 17-year-old boy comes to the physician because of a 3-month history of worsening acne. Treatment over the past year with tetracycline had been effective. His symptoms began when he started taking the medication in the morning with a glass of milk. Which of the following best explains the ineffectiveness of tetracycline in this patient?

A 61-year-old man is prescribed fluoxetine for major depressive disorder. This drug has its initial effects on neurons arising in which of the following structures?

A 42-year-old woman with type 2 diabetes mellitus comes to the physician because of a 1-day history of increasingly severe right knee pain. She now has difficulty walking because of the pain. She recalls no trauma to the knee and has never had similar symptoms. She is 152 cm (5 ft) tall and weighs 100 kg (220 lb); BMI is 43 kg/m2. Her temperature is 39.3°C (102.7°F), pulse is 110/min, respirations are 12/min, and blood pressure is 160/90 mm Hg. Physical examination shows a 10-cm area of erythema surrounding the right knee, which is warm to the touch and exquisitely tender with movement. There is a moderate effusion. Arthrocentesis yields cloudy yellow synovial fluid. Analysis of the synovial fluid shows a leukocyte count of 90,000/mm3 (95% neutrophils) and no crystals. A Gram stain of the fluid shows numerous segmented neutrophils but no organisms. Which of the following is the most likely cause of the findings in this patient?

A 35-year-old woman comes to the physician because of a 2-day history of painful blisters on her upper and lower lips. She has a 10-year history of similar symptoms interspersed with periods of remission. A photograph of the lesions is shown. Which of the following neuronal processes was most likely involved in the initial establishment of the viral infection in this patient?

A 23-year-old woman comes to the physician because of a 2-week history of increasingly severe itching and yellow-tinged skin. Three months ago, she started taking a combination oral contraceptive. She does not smoke. She consumes two to three alcoholic beverages only on the weekends. Physical examination shows mild jaundice and scleral icterus. The liver span is 11 cm with no tenderness. Serum studies show:

Serologic studies for acute viral hepatitis are negative. Which of the following is the most likely cause of these findings?

A 42-year-old man is brought to the emergency department 1 hour after police found him wandering the street. He has a 5-year history of gout. There is no odor of alcohol, but he is drowsy and ataxic. Physical examination shows severe jaundice, prominent periumbilical veins, and several cutaneous spider angiomata. Abdominal examination shows splenomegaly and ascites. There is a flapping, up-and-down motion of the hands when his arms are outstretched horizontally. His hemoglobin concentration is 10.8 g/dL. Test of the stool for occult blood is positive. The arm motions and drowsiness are best explained by which of the following?

A 4-year-old girl with chronic otitis media is brought to the physician by her mother because of a 5-day history of recurrence of symptoms. The mother says that her daughter had a mild cough that began 8 days ago and progressed to a sore throat and ear pain during the next 3 days. The patient appears irritable and is pulling at her right ear. Otoscopic examination shows fluid behind the tympanic membrane. Which of the following best describes the anatomic pathway of the spread of infection from this patient’s throat?

A 20-year-old man is brought to the physician by his mother because of bizarre behavior for 6 months. Although he had always been a good student, he failed all his classes at college last term. He no longer showers or shaves, and his appearance has become disheveled and unkempt. He appears distracted at the beginning of the interview and then begins talking nonstop to unseen people in the corner of the examining room. His mother looks upset and says, “It seems as if he’s hearing voices all the time now. He’s really scaring our family.” Which of the following initial responses by the physician is most appropriate?

A 1-month-old boy with X-linked severe combined immunodeficiency is enrolled in a gene therapy trial. Bone marrow stem cells are extracted from the patient and are treated ex vivo with a retrovirus expressing the wild-type gene. Although the patient initially responds well, 30 months after treatment he develops a form of T-lymphocyte leukemia. Molecular studies show that the T lymphocytes are monoclonal. Which of the following viral processes is the most likely cause of the leukemia in this patient?

A 67-year-old man comes to the physician because of a 2-month history of pain in his feet. The discomfort is more severe in bed at night and is relieved by taking a hot bath. He has type 2 diabetes mellitus treated with glipizide. His pulse is 60/min, respirations are 12/min, and blood pressure is 130/88 mm Hg. Strength is normal and symmetric in the distal and proximal upper and lower extremities. The Achilles deep tendon reflexes are decreased, and quadriceps deep tendon reflexes are normal. Sensation to pinprick and vibration is decreased from just above the ankles distally. This patient is most likely to describe his pain as which of the following?

An 8-year-old boy is admitted to the hospital because of severe flank pain and blood in his urine. He has had intellectual developmental disorder since early infancy. Examination shows choreoathetosis and self-mutilation of the lips and fingers. His serum uric acid concentration is increased. Urinalysis shows numerous uric acid crystals and erythrocytes. The most likely cause of the hyperuricemia is deficient activity of which of the following enzymes?

A 63-year-old man from southern China has had a bloody nasal discharge for the past 5 months. Physical examination shows an enlarged, fixed lymph node in the upper posterior cervical triangle of the left neck. Examination of tissue obtained on needle biopsy of the lymph node shows neoplastic cells that are positive for keratin and Epstein-Barr nuclear antigen. Which of the following is the most likely diagnosis?

In an experimental model of mild thermal injury to skin (a single application of 54°C for 20 seconds), the following pattern of extravasation of intravenously administered dye is observed. Administration of an antihistamine prior to thermal injury would have significantly blunted the extent of dye extravasation observed at which of the following labeled sites?

A 50-year-old woman has azotemia. Renal ultrasonography shows bilateral hydroureters and hydronephrosis. The most likely cause of these findings is primary carcinoma of which of the following?

A 2-year-old boy is brought to the physician by his mother because of a 3-week history of increased irritability. He is at the 10th percentile for height, 5th percentile for weight, and 80th percentile for head circumference. Physical examination shows evidence of hydrocephalus. A CT scan of the head shows a cyst-like dilation of the fourth ventricle, hypoplastic cerebellar hemispheres, and an enlarged posterior fossa with high tentorium cerebelli. Which of the following subdivisions of the neural tube was most likely affected in this patient during prenatal development?

A 64-year-old man undergoes surgical repair of an abdominal aortic aneurysm. During the repair, the left testicular artery is ligated. Anastomotic supply from which of the following arteries will maintain adequate arterial supply to the left testis in this patient?

Diisopropyl fluorophosphate, a potent inhibitor of acetylcholinesterase, reacts with which of the following specific amino acids at the active site of the enzyme?

A 68-year-old man comes to the physician because of difficulty swallowing solids for 2 months, contrast show indentation and posterior displacement of the esophagus. Enlargement of which He has a history of dilated cardiomyopathy. X-rays of the esophagus with barium of the following structures is the most likely cause of the dysphagia?

A 55-year-old man comes to the physician because of pain and stiffness of his right hand and wrist for 3 months. The pain is exacerbated by hand movement and is relieved by rest. He was a professional boxer for 15 years. Physical examination shows moderate swelling over the dorsum of the right wrist. Examination of fluid aspirated from the wrist shows:

Which of the following is the most likely cause of this patient’s condition?

An investigator is conducting a randomized, double-blind, placebo-controlled clinical trial of a new medication for the treatment of mild insomnia in adults. A total of  2000 participants are enrolled in the study and randomized to one of two groups: 1000 participants receive the new medication (Group 1), and 1000 participants receive a placebo that appears identical to the medication (Group 2). Participants in both groups are instructed to take one pill 30 minutes before bedtime each day and to keep a sleep diary. After 1 month, each participant is interviewed, and the daily sleep diaries are reviewed. At follow-up, it is determined that 200 participants in Group 1 and 50 participants in Group 2 did not take the pill as directed. In accordance with intention-to-treat analysis, how should the data pertaining to all individuals who did not adhere to the instructions be treated?

A 24-year-old nulligravid woman comes to the office because of a 6-month history of chronic headache and vision difficulties. She also recently had several episodes of milky discharge from her breasts. Menses occur at irregular 50- to 90-day intervals; her last menstrual period was 6 months ago. She takes an oral contraceptive continuously and does not have withdrawal bleeding. Pulse is 80/min, respirations are 14/min, and blood pressure is 110/78 mm Hg. Ophthalmologic examination shows bitemporal hemianopia. Physical examination shows galactorrhea. Urine pregnancy test result is negative. MRI of the brain shows a 2-cm mass. Which of the following labeled structures in the normal MRI of the brain is the most likely location of the mass in this patient?

A 72-year-old woman is admitted to the hospital because of an acute myocardial infarction. She undergoes cardiac catheterization. Angiography shows a left dominant circulation, and a 90% narrowing of the artery supplying the diaphragmatic surface and atrioventricular node of the heart. A balloon angioplasty is scheduled during which a stent will be inserted in the narrowed vessel. The catheter and the balloon must be passed through which of the following vessels (stated in order) to reach the narrowed vessel?

A 34-year-old woman has a 3-year history of recurring episodes of tenesmus, mucoid bloody diarrhea, and cramping abdominal pain. A section of bowel removed following a severe episode is shown. Which of the following is the most likely diagnosis?