Laboratory findings US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Laboratory findings. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Laboratory findings US Medical PG Question 1: A 52-year-old man comes to the emergency department because of a 3-week history of abdominal distention, yellow coloring of the skin, and dark urine. He also reports malaise and progressive shortness of breath, associated with slight exertion, for several weeks. The patient is a chronic drinker, and he was diagnosed with cirrhosis 2 years ago. He was warned to stop drinking alcohol, but he continues to drink. He hasn't accepted any more testing and has refused to visit the doctor until now. His vital signs are heart rate 62/min, respiratory rate 26/min, temperature 37.4°C (99.3°F), and blood pressure 117/95 mm Hg. On physical examination, there is dyspnea and polypnea. Skin and sclera are jaundiced. The abdomen has visible collateral circulation and looks distended. There is diffuse abdominal pain upon palpation in the right hemiabdomen, and the liver is palpated 10 cm below the right costal border. The legs show significant edema. CT scan shows cirrhosis with portal hypertension and collateral circulation. During the fifth day of his hospital stay, the patient presents with oliguria and altered mental status. Laboratory studies show:
Day 1
Day 5
Hemoglobin
12.1 g/dL
11.2 g/dL
Hematocrit
33.3%
31.4%
Leukocyte count
7,000/mm3
6,880/mm3
Platelet count
220,000/mm3
134,000/mm3
Total bilirubin
20.4 mg/dL
28.0 mg/dL
Direct bilirubin
12.6 mg/dL
21.7 mg/dL
Creatinine
2.2 mg/dL
2.9 mg/dL
Albumin
3.4 g/dL
2.6 g/dL
PT
15 s
16.9 s
aPTT
19 s
35 s
Urinalysis
Negative for nitrite
Negative for leukocyte esterase
0–2 RBCs per high power field
0–1 WBC per high power field
No evidence of casts or proteinuria
What is the most likely cause of this patient's increased creatinine?
- A. Hepatorenal syndrome (Correct Answer)
- B. Chronic kidney disease
- C. Pyelonephritis
- D. Acute tubular necrosis
- E. Glomerulonephritis
Laboratory findings Explanation: ***Hepatorenal syndrome***
- This patient with **decompensated cirrhosis** and **oliguria** exhibits a rapid increase in **creatinine** (2.2 to 2.9 mg/dL over 4 days) without evidence of intrinsic kidney disease (negative urinalysis with no casts, minimal proteinuria). This points toward **Hepatorenal Syndrome (HRS)**, a severe complication of advanced liver disease.
- The **bland urinalysis** is the key diagnostic feature of HRS, distinguishing it from acute tubular necrosis. HRS results from severe vasoconstriction of renal arteries in the setting of splanchnic vasodilation from portal hypertension.
- The development of **altered mental status** along with worsening renal function further supports HRS, as it reflects progressive hepatic decompensation and hepatic encephalopathy.
*Chronic kidney disease*
- While patients with cirrhosis can develop CKD, the **rapid onset** of renal failure and oliguria over just 4 days, coupled with normal urinalysis, is less typical for primary chronic kidney disease exacerbation.
- CKD usually presents with more gradual changes in creatinine and may show signs of kidney damage (like proteinuria or casts) on urinalysis, which are absent here.
*Pyelonephritis*
- **Pyelonephritis**, a kidney infection, would typically present with fever, flank pain, and significant abnormalities on urinalysis such as **leukocyte esterase**, **nitrites**, and **white blood cell casts**, none of which are present.
- The absence of infectious markers in the urine makes pyelonephritis an unlikely cause of the acute renal deterioration.
*Acute tubular necrosis*
- **Acute tubular necrosis (ATN)**, often caused by ischemia or nephrotoxins, would typically show signs of tubular damage on urinalysis, such as **muddy brown casts** and renal tubular epithelial cells.
- The urinalysis in this case is bland, with no evidence of casts or significant cellular debris, ruling out ATN as the primary diagnosis.
*Glomerulonephritis*
- **Glomerulonephritis** would typically present with **hematuria**, **proteinuria**, and potentially **red blood cell casts** on urinalysis, indicating glomerular inflammation.
- The patient's urinalysis is benign, showing no red blood cell casts or significant proteinuria, making glomerulonephritis an unlikely diagnosis.
Laboratory findings US Medical PG Question 2: A 6-year-old boy presents to his pediatrician accompanied by his mother for evaluation of a rash. The rash appeared a little over a week ago, and since that time the boy has felt tired. He is less interested in playing outside, preferring to remain indoors because his knees and stomach hurt. His past medical history is significant for an upper respiratory infection that resolved uneventfully without treatment 2 weeks ago. Temperature is 99.5°F (37.5°C), blood pressure is 115/70 mmHg, pulse is 90/min, and respirations are 18/min. Physical exam shows scattered maroon macules and papules on the lower extremities. The abdomen is diffusely tender to palpation. There is no cervical lymphadenopathy or conjunctival injection. Which of the following will most likely be found in this patient?
- A. Coronary artery aneurysms
- B. Leukocytoclastic vasculitis (Correct Answer)
- C. Thrombocytopenia
- D. Mitral regurgitation
- E. Occult malignancy
Laboratory findings Explanation: ***Leukocytoclastic vasculitis***
- This patient presents with symptoms highly suggestive of **Henoch-Schönlein Purpura (HSP)**, including a preceding URI, fatigue, low-grade fever, **abdominal pain**, and a **palpable purpura** primarily on the lower extremities.
- HSP is characterized by IgA-mediated **small-vessel vasculitis**, which histologically presents as leukocytoclastic vasculitis with IgA deposition on immunofluorescence.
*Coronary artery aneurysms*
- **Coronary artery aneurysms** are a classic complication of **Kawasaki disease**, not Henoch-Schönlein Purpura.
- Kawasaki disease presents with different clinical features, including prolonged fever, conjunctival injection, oral changes, and cervical lymphadenopathy.
*Thrombocytopenia*
- **Thrombocytopenia** is characterized by a low platelet count and often presents with petechiae, purpura, and bleeding, but the rash in HSP is due to inflammation and extravasation of red blood cells, not low platelets.
- Platelet counts in HSP are typically **normal** or can be slightly elevated as an acute phase reactant.
*Mitral regurgitation*
- **Mitral regurgitation** is a common manifestation of **rheumatic fever**, particularly after recurrent episodes, caused by valvular damage.
- Rheumatic fever is also preceded by infection (Group A Strep) but involves different symptoms like migratory polyarthritis, carditis, chorea, erythema marginatum, and subcutaneous nodules, which are not described here.
*Occult malignancy*
- While an **occult malignancy** can cause paraneoplastic syndromes or constitutional symptoms, the specific constellation of symptoms, including the migratory rash, abdominal pain, and preceding URI, points much more strongly to **HSP** in a 6-year-old.
- The presentation is more consistent with an acute, inflammatory process rather than a chronic, insidious malignant one.
Laboratory findings US Medical PG Question 3: A 44-year-old woman with recurrent urinary tract infections is brought to the emergency department by ambulance after sudden onset of severe headache 30 minutes ago. She has a history of occasional, mild headaches in the morning. There is no other history of serious illness. Both her father and her paternal grandmother died of chronic kidney disease. Her temperature is 37.2°C (99.1°F) and blood pressure is 145/90 mm Hg. Physical examination shows neck stiffness. When her hip is flexed, she is unable to fully extend her knee because of pain. Lumbar puncture performed 12 hours after headache onset yields 10 mL of yellow-colored fluid with no leukocytes. Which of the following is the most likely predisposing factor for this patient's current condition?
- A. Cerebral atrophy
- B. Saccular aneurysm (Correct Answer)
- C. Arterial atherosclerosis
- D. Bacterial infection
- E. Hypercoagulable state
Laboratory findings Explanation: ***Saccular aneurysm***
- The sudden onset of a **severe headache**, **neck stiffness**, positive **Kernig's sign** (inability to fully extend the knee when the hip is flexed), and **xanthochromic cerebrospinal fluid (CSF)** strongly suggest **subarachnoid hemorrhage (SAH)**.
- **Saccular (berry) aneurysms** are the most common cause of non-traumatic SAH, and the patient's family history of chronic kidney disease (potentially indicating **polycystic kidney disease**) is a risk factor for their development.
*Cerebral atrophy*
- **Cerebral atrophy** is a process involving loss of neurons and neuronal connections, typically associated with aging or neurodegenerative diseases, and does not directly predispose to acute subarachnoid hemorrhage.
- While it can be associated with some forms of vascular disease, it is not a primary risk factor for the sudden rupture of a cerebral aneurysm.
*Arterial atherosclerosis*
- **Atherosclerosis** usually causes **ischemic strokes** or **transient ischemic attacks** due to plaque rupture or stenosis, or intracerebral hemorrhages from rupture of small vessels.
- It is not a primary predisposing factor for **saccular aneurysm rupture** leading to subarachnoid hemorrhage, which typically involves congenital or acquired defects in the arterial wall.
*Bacterial infection*
- A **bacterial infection** of the central nervous system would lead to symptoms of meningitis (fever, altered mental status) and a CSF profile showing **elevated leukocytes**, low glucose, and high protein, none of which are consistent with this patient's presentation.
- The patient's CSF showed **no leukocytes**, ruling out a bacterial cause for meningeal irritation.
*Hypercoagulable state*
- A **hypercoagulable state** increases the risk for **thrombotic events** such as deep vein thrombosis, pulmonary embolism, or ischemic stroke.
- It does not predispose to the spontaneous rupture of a cerebral aneurysm and subsequent subarachnoid hemorrhage, which is a bleeding event.
Laboratory findings US Medical PG Question 4: A 33-year-old man with a history of IV drug and alcohol abuse presents to the emergency department with back pain. He states that his symptoms started 3 days ago and have been gradually worsening. His temperature is 102°F (38.9°C), blood pressure is 127/68 mmHg, pulse is 120/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for tenderness over the mid thoracic spine. Laboratory values are only notable for a leukocytosis and an elevated ESR and CRP. Which of the following is the most likely diagnosis?
- A. Degenerative spine disease
- B. Herniated nucleus pulposus
- C. Musculoskeletal strain
- D. Osteomyelitis (Correct Answer)
- E. Spinal epidural hematoma
Laboratory findings Explanation: ***Osteomyelitis***
- The patient's history of **IV drug abuse** is a major risk factor for **hematogenous osteomyelitis**, especially vertebral osteomyelitis.
- The presence of **fever**, **localized spinal tenderness**, **leukocytosis**, and elevated **ESR** and **CRP** are classic signs of infection.
*Degenerative spine disease*
- This condition typically presents with **chronic pain** and insidious onset, not acute fever and inflammatory markers.
- While it can cause back pain, it is not associated with systemic signs of infection or a rapid worsening course like in this case.
*Herniated nucleus pulposus*
- Primarily causes **radicular pain** and neurological deficits due to nerve compression, often without systemic symptoms.
- There are no signs of infection, fever, or elevated inflammatory markers associated with a simple herniated disc.
*Musculoskeletal strain*
- This would present with localized pain, but rarely with **fever**, **leukocytosis**, and markedly elevated inflammatory markers.
- It is typically a self-limiting condition with symptoms that would not progressively worsen over three days with systemic signs of infection.
*Spinal epidural hematoma*
- This is characterized by sudden, severe back pain and often rapid onset neurological deficits, particularly in patients on anticoagulants or with coagulopathies.
- It would not typically present with **fever** and elevated inflammatory markers suggestive of an infection.
Laboratory findings US Medical PG Question 5: A 25-year-old man of Mediterranean descent makes an appointment with his physician because his skin and sclera have become yellow. He complains of fatigue and fever that started at the same time icterus appeared. On examination, he is tachycardic and tachypneic. The oxygen (O2) saturation is < 90%. He has increased unconjugated bilirubin, hemoglobinemia, and an increased number of reticulocytes in the peripheral blood. What is the most likely diagnosis?
- A. Microcytic anemia caused by iron deficiency
- B. Aplastic anemia
- C. Autoimmune hemolytic anemia (AIHA)
- D. Anemia caused by renal failure
- E. Hemolytic anemia caused by glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency) (Correct Answer)
Laboratory findings Explanation: ***Hemolytic anemia caused by glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency)***
- The patient's presentation with **jaundice**, **fatigue**, fever, **tachycardia**, **tachypnea**, and **low oxygen saturation** points to an acute hemolytic crisis.
- The laboratory findings of **increased unconjugated bilirubin**, **hemoglobinemia** (evidence of red blood cell destruction), and **increased reticulocytes** (bone marrow's attempt to compensate for red blood cell loss) are classic for hemolytic anemia. A young man of **Mediterranean descent** makes G6PD deficiency a strong possibility, as it is common in this population and can be triggered by various factors leading to oxidative stress.
*Microcytic anemia caused by iron deficiency*
- **Iron deficiency anemia** typically presents with **microcytic hypochromic red blood cells**, and while it causes fatigue and pallor, it does not typically lead to acute jaundice and hemoglobinemia.
- Reticulocyte count is usually normal or only mildly elevated, not significantly increased as seen in rapid red blood cell destruction.
*Aplastic anemia*
- **Aplastic anemia** is characterized by **pancytopenia** (decreased red blood cells, white blood cells, and platelets) due to bone marrow failure.
- It does not present with signs of hemolytic crisis such as jaundice, hemoglobinemia, or increased reticulocytes.
*Autoimmune hemolytic anemia (AIHA)*
- While AIHA causes **hemolytic anemia** with similar lab findings (jaundice, increased unconjugated bilirubin, reticulocytosis), the context of a young man of **Mediterranean descent** makes G6PD deficiency a more likely primary consideration, especially without specific triggers for AIHA or a positive direct Coombs test result.
- AIHA involves autoantibodies against red blood cells.
*Anemia caused by renal failure*
- Anemia due to **renal failure** is primarily caused by decreased production of **erythropoietin** leading to **normocytic, normochromic anemia**.
- It does not involve acute hemolysis, jaundice, hemoglobinemia, or increased reticulocytes.
Laboratory findings US Medical PG Question 6: A 69-year-old woman is brought to the emergency department because of fatigue and lethargy for 5 days. She has also had weakness and nausea for the last 3 days. She has sarcoidosis, major depressive disorder, and hypertension. She had a stroke 5 years ago. Current medications include aspirin, nifedipine, prednisolone, fluoxetine, and rosuvastatin, but she has not taken any of her medications for 7 days due to international travel. Her temperature is 36.1°C (96.9°F), pulse is 95/min, and blood pressure is 85/65 mm Hg. She is lethargic but oriented. Examination shows no other abnormalities. Her hemoglobin concentration is 13.4 g/dL and leukocyte count is 9,600/mm3. Both serum cortisol and ACTH levels are decreased. This patient is most likely to have which of the following additional laboratory abnormalities?
- A. Hyperglycemia
- B. Hyperkalemia
- C. Hyponatremia (Correct Answer)
- D. Hypokalemia
- E. Normal anion gap metabolic acidosis
Laboratory findings Explanation: ***Hyponatremia***
- This patient has **secondary adrenal insufficiency** due to **HPA axis suppression** from chronic prednisolone use, precipitated by abrupt withdrawal after 7 days without medication.
- **Both decreased cortisol and ACTH** confirm secondary (central) adrenal insufficiency, distinguishing it from primary adrenal insufficiency where ACTH would be elevated.
- **Hyponatremia** develops due to **cortisol deficiency** impairing free water excretion, leading to dilutional hyponatremia—a hallmark laboratory finding in adrenal insufficiency.
- Clinical features include **fatigue, lethargy, hypotension, nausea, and weakness**, consistent with adrenal crisis.
*Hyperglycemia*
- While **glucocorticoids** cause hyperglycemia, **cortisol deficiency** in adrenal insufficiency leads to **impaired gluconeogenesis** and a tendency toward **hypoglycemia**, not hyperglycemia.
- The patient's presentation with hypotension and weakness is consistent with adrenal crisis, not hyperglycemia.
*Hyperkalemia*
- **Hyperkalemia** is characteristic of **primary adrenal insufficiency** (Addison's disease) due to **aldosterone deficiency** affecting the renin-angiotensin-aldosterone system.
- In **secondary adrenal insufficiency**, the hypothalamic-pituitary axis is suppressed but the **renin-angiotensin-aldosterone system remains intact**, so aldosterone secretion is preserved and significant hyperkalemia does not occur.
*Hypokalemia*
- **Hypokalemia** is not a typical feature of adrenal insufficiency and is more commonly associated with diuretic use, primary hyperaldosteronism, or other conditions not present in this case.
- The patient's condition reflects cortisol deficiency with preserved aldosterone function.
*Normal anion gap metabolic acidosis*
- **Normal anion gap metabolic acidosis** occurs in conditions like **renal tubular acidosis** or **diarrhea**, but is not a direct or common consequence of secondary adrenal insufficiency.
- The acute presentation with hypotension and electrolyte disturbance (hyponatremia) is the primary metabolic derangement in this case.
Laboratory findings US Medical PG Question 7: A patient in a phase 1 trial for a novel epoxide reductase inhibitor, being studied for stroke prophylaxis, develops pain and erythema on the right thigh two days after starting the trial. This rapidly progresses to a purpuric rash with necrotic bullae within 24 hours. Lab results show a PTT of 29 seconds, PT of 28 seconds, and INR of 2.15. What is the most likely pathogenesis of this condition?
- A. Decreased plasmin activity
- B. Decreased platelet count
- C. Decreased protein C levels (Correct Answer)
- D. Increased factor VIII activity
- E. Decreased antithrombin III activity
Laboratory findings Explanation: ***Decreased protein C levels***
- The clinical presentation of **pain and erythema progressing to purpuric rash with necrotic bullae** within 2-3 days of starting therapy, along with elevated PT/INR, is **pathognomonic for warfarin-induced skin necrosis**.
- This novel **epoxide reductase inhibitor** works like warfarin by inhibiting **vitamin K epoxide reductase**, which depletes all vitamin K-dependent factors.
- **Protein C and protein S** (natural anticoagulants) have **short half-lives** (6-8 hours) and drop rapidly, while procoagulant factors II, VII, IX, and X have longer half-lives (24-60 hours).
- This creates a **transient hypercoagulable state** in the first 2-3 days of therapy with **low protein C/S** but relatively preserved procoagulant factors, leading to **microvascular thrombosis** and skin necrosis.
- Most common in patients with **hereditary protein C or S deficiency** or those receiving loading doses.
*Decreased antithrombin III activity*
- Antithrombin III is **not a vitamin K-dependent factor** and is not directly affected by epoxide reductase inhibitors.
- Decreased antithrombin III would cause thrombosis but does not explain the **specific temporal relationship** and mechanism of warfarin-induced skin necrosis.
- Antithrombin III deficiency causes **venous thromboembolism**, not the characteristic cutaneous necrosis pattern.
*Decreased plasmin activity*
- Plasmin is involved in **fibrinolysis** and is not affected by vitamin K epoxide reductase inhibitors.
- Decreased plasmin activity would impair clot breakdown but does not explain the **early hypercoagulable state** specific to warfarin initiation.
- This mechanism is not relevant to warfarin-induced skin necrosis.
*Decreased platelet count*
- The lab values provided show **elevated PT/INR**, consistent with coagulation factor depletion, not thrombocytopenia.
- Thrombocytopenia causes **petechiae and mucosal bleeding**, not the large **necrotic bullae** seen here.
- Platelet count is not affected by epoxide reductase inhibitors.
*Increased factor VIII activity*
- Factor VIII is **not a vitamin K-dependent factor** and is not depleted by epoxide reductase inhibitors.
- While elevated factor VIII can contribute to hypercoagulability, it does not explain the **specific mechanism and timeline** of warfarin-induced skin necrosis.
- This is not the primary pathogenesis of this condition.
Laboratory findings US Medical PG Question 8: A 2-year-old boy is brought to the emergency department by his parents because of facial swelling that has now progressed to total body swelling. He also complains of nausea and abdominal pain. The child was in his usual state of health a week ago when they first notice swelling around his eyes. A few days later his legs started to swell. The boy was born at 39 weeks gestation via spontaneous vaginal delivery. He is up to date on all vaccines and is meeting all developmental milestones. Today, his blood pressure is 104/60 mm Hg, the heart rate is 90/min, the respiratory rate is 25/min, and the temperature is 37.1°C (98.8°F). On examination, he has facial edema, abdominal shifting dullness, and bilateral leg edema up to the knees. Urine dipstick shows 4+ protein and urinalysis shows fatty casts. Serum albumin is 2.2 g/dL. Which of the following is the most likely etiology of this patient condition?
- A. Acute glomerulonephritis
- B. Minimal change disease (Correct Answer)
- C. Congestive heart failure
- D. Kwashiorkor
- E. Protein-losing enteropathy
Laboratory findings Explanation: ***Minimal change disease***
- This patient presents with **generalized edema**, **heavy proteinuria** (4+ protein with fatty casts), and **hypoalbuminemia** (< 2.5 g/dL), classic findings of **nephrotic syndrome**.
- **Minimal change disease** is the most common cause of nephrotic syndrome in children, typically presenting between 2 and 6 years of age, matching the patient's age and clinical picture.
*Acute glomerulonephritis*
- This condition is typically characterized by **hematuria**, **hypertension**, and **mild proteinuria**, often following a streptococcal infection.
- The patient's presentation with **massive proteinuria** and absence of hematuria or significant hypertension makes acute glomerulonephritis less likely.
*Congestive heart failure*
- While CHF can cause edema, it is usually accompanied by signs of **cardiac dysfunction** such as tachycardia, tachypnea, and an enlarged heart on imaging, which are not described.
- The primary cause of edema in CHF is **fluid overload** due to impaired cardiac output, not massive proteinuria and hypoalbuminemia as seen here.
*Kwashiorkor*
- This is a form of **severe protein malnutrition** leading to edema and abdominal distension, often seen in regions with food scarcity.
- The clinical context does not suggest malnutrition, and the presence of **heavy proteinuria** points to a renal pathology rather than a primary nutritional deficiency.
*Protein-losing enteropathy*
- This condition involves excessive protein loss through the **gastrointestinal tract**, leading to hypoalbuminemia and edema.
- However, it typically presents with **diarrhea** and malabsorption symptoms, which are not reported in this patient.
Laboratory findings US Medical PG Question 9: A 3500-g (7.7-lbs) girl is delivered at 39 weeks' gestation to a 27-year-old woman, gravida 2, para 1. Apgar scores are 8 and 9 at 1 and 5 minutes, respectively. The mother had regular prenatal visits throughout the pregnancy. She did not smoke or drink alcohol. She took multivitamins as prescribed by her physician. The newborn appears active. The girl's temperature is 37°C (98.6°F), pulse is 120/min, and blood pressure is 55/35 mm Hg. Examination in the delivery room shows clitoromegaly. One day later, laboratory studies show:
Hemoglobin 12.8 g/dL
Leukocyte count 6,000/mm3
Platelet count 240,000/mm3
Serum
Na+ 133 mEq/L
K+ 5.2 mEq/L
Cl− 101 mEq/L
HCO3− 21 mEq/L
Urea nitrogen 15 mg/dL
Creatinine 0.8 mg/dL
Ultrasound of the abdomen and pelvis shows normal uterus and normal ovaries. Which of the following is the most appropriate next step in the management of this newborn patient?
- A. Spironolactone therapy
- B. Estrogen replacement therapy
- C. Dexamethasone therapy
- D. Genital reconstruction surgery
- E. Hydrocortisone and fludrocortisone therapy (Correct Answer)
Laboratory findings Explanation: ***Hydrocortisone and fludrocortisone therapy***
- The newborn presents with **clitoromegaly** and electrolyte abnormalities including **hyponatremia** and **hyperkalemia**, which are characteristic findings of **salt-wasting congenital adrenal hyperplasia (CAH)**.
- CAH is caused by a deficiency in 21-hydroxylase enzyme, leading to inadequate production of cortisol and aldosterone. **Hydrocortisone** (glucocorticoid) and **fludrocortisone** (mineralocorticoid) are essential for replacing these deficient hormones and preventing adrenal crisis.
*Spironolactone therapy*
- **Spironolactone** is an **aldosterone antagonist** and would worsen the existing salt-wasting state and hyperkalemia seen in CAH.
- It works by blocking aldosterone, leading to increased sodium excretion and potassium retention, which is the opposite of what is needed in CAH.
*Estrogen replacement therapy*
- **Estrogen replacement therapy** is not indicated at this stage. It would not address the underlying hormonal deficiencies (cortisol and aldosterone) or correct the electrolyte imbalances in CAH.
- Estrogen is involved in female sexual development but does not play a primary role in the acute management of adrenal insufficiency in newborns with CAH.
*Dexamethasone therapy*
- **Dexamethasone** is a potent **glucocorticoid**, but it is generally not the first-line treatment for chronic management in infants with CAH due to its prolonged half-life and higher risk of growth suppression compared to hydrocortisone.
- While it could address the cortisol deficiency, it does not provide mineralocorticoid activity, which is crucial for managing the salt-wasting component.
*Genital reconstruction surgery*
- **Genital reconstruction surgery** may be considered later in life for cosmetic or functional reasons, but it is not the immediate or most appropriate next step in managing a newborn with CAH.
- The immediate priority is to stabilize the child's hormonal and electrolyte balance to prevent potentially life-threatening adrenal crisis.
Laboratory findings US Medical PG Question 10: A 1-month-old boy is brought in by his mother for episodes of “not breathing.” She reports noticing that the patient will occasionally stop breathing while he’s sleeping, and that these episodes have been occurring more frequently. The patient was born at 32 weeks due to placental insufficiency. He was in the neonatal intensive care unit for 1 day to be placed on a respirator. During prenatal testing, it was revealed that the mother was not immune to rubella, but she otherwise had an uncomplicated pregnancy. She has no medical conditions and took only prenatal vitamins. The patient has a 3-year-old sister who is healthy. His father has a “heart condition.” The patient’s temperature is 98°F (36.7°C), blood pressure is 91/55 mmHg, pulse is 207/min, and respirations are 50/min with an oxygen saturation of 97% on room air. Physical examination is notable for pale conjunctiva. Labs are obtained, as shown below:
Leukocyte count: 10,000/mm^3 with normal differential
Hemoglobin: 8.2 g/dL
Hematocrit: 28%
Mean corpuscular volume (MCV): 100 um^3
Platelet count: 300,000/mm^3
Reticulocyte count: 0.8% (normal range: 2-6%)
Lactate dehydrogenase: 120 U/L (normal range: 100-250 U/L)
A peripheral smear reveals normocytic and normochromic red blood cells. Which of the following is a mechanism for the patient’s most likely diagnosis?
- A. Red blood cell membrane defect
- B. Minor blood group incompatibility
- C. Hemoglobinopathy
- D. Impaired erythropoietin production (Correct Answer)
- E. Congenital infection
Laboratory findings Explanation: ***Impaired erythropoietin production***
- This patient presents with **anemia of prematurity**, indicated by **normocytic, normochromic anemia** with a **low reticulocyte count** in a premature infant.
- The primary mechanism for **anemia of prematurity** is a blunted erythropoietin response to early anemia, leading to **impaired red blood cell production**.
*Red blood cell membrane defect*
- Conditions like **hereditary spherocytosis** or **elliptocytosis** involve red blood cell membrane defects, which typically lead to **hemolytic anemia** with elevated reticulocyte count.
- The patient's **low reticulocyte count** and normal LDH (lactate dehydrogenase is a marker of hemolysis) make a primary membrane defect less likely.
*Minor blood group incompatibility*
- **Minor blood group incompatibilities** (e.g., ABO, Kell, Duffy) typically cause **hemolytic disease of the newborn**, characterized by **elevated reticulocyte count**, **hyperbilirubinemia**, and signs of hemolysis.
- The patient exhibits no signs of hemolysis, such as elevated bilirubin or LDH, and has a normal reticulocyte count.
*Hemoglobinopathy*
- **Hemoglobinopathies** (e.g., sickle cell anemia, thalassemia) involve structural or quantitative defects in hemoglobin, often leading to **microcytic** or **hemolytic anemias** with **elevated reticulocyte counts** or specific red blood cell morphologies.
- The patient's **normocytic, normochromic anemia** and absent signs of hemolysis do not fit typical presentations of common hemoglobinopathies at this age.
*Congenital infection*
- Certain **congenital infections** (e.g., parvovirus B19, congenital syphilis, rubella) can cause anemia by directly suppressing erythropoiesis or causing hemolysis.
- While the mother was not immune to rubella, there are no other clinical signs of congenital infection, and the **normocytic, normochromic anemia** with low reticulocytes is more characteristic of anemia of prematurity.
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