A 19-year-old male with cystic fibrosis is evaluated in the clinic for regular health maintenance. He is compliant with his respiratory therapy, but states that he often "forgets" to take the medications before he eats. A panel of labs is drawn which reveals a moderate vitamin D deficiency. Which of the following electrolyte abnormalities might be seen as a consequence of vitamin D deficiency?
Q62
A 43-year-old woman is found in the hospital to have a plasma sodium concentration of 126 mg/dL. She was hospitalized after she expressed suicidal ideations and was started on a medication for major depressive disorder. Her past medical history is significant for diabetes for which she is currently taking metformin. Her blood pressure while in the hospital has been around 130/85 mmHg and she is not taking any other medications. Laboratory studies show a serum osmolality of 265 mOsm/kg. Which of the following best describes the cell bodies of the cells that are behaving abnormally in this patient?
Q63
A 35-year-old woman, gravida 2, para 1, at 16 weeks' gestation comes to the office for a prenatal visit. She reports increased urinary frequency but otherwise feels well. Pregnancy and delivery of her first child were uncomplicated. Her vital signs are within normal limits. Pelvic examination shows a uterus consistent in size with a 16-week gestation. Urinalysis shows mild glucosuria. Laboratory studies show a non-fasting serum glucose concentration of 110 mg/dL. Which of the following is the most likely explanation for this patient's glucosuria?
Q64
A 68-year-old woman presents to her primary care physician for a regular check-up. She complains of swelling of her legs and face, which is worse in the morning and decreases during the day. She was diagnosed with type 2 diabetes mellitus a year ago and prescribed metformin, but she has not been compliant with it preferring 'natural remedies' over the medications. She does not have a history of cardiovascular disease or malignancy. Her vital signs are as follows: blood pressure measured on the right hand is 130/85 mm Hg, on the left hand, is 110/80 mm Hg, heart rate is 79/min, respiratory rate is 16/min, and the temperature is 36.6℃ (97.9°F). Physical examination reveals S1 accentuation best heard in the second intercostal space at the right sternal border. Facial and lower limbs edema are evident. The results of the laboratory tests are shown in the table below.
Fasting plasma glucose 164 mg/dL
HbA1c 10.4%
Total cholesterol 243.2 mg/dL
Triglycerides 194.7 mg/dL
Creatinine 1.8 mg/dL
Urea nitrogen 22.4 mg/dL
Ca2+ 9.6 mg/dL
PO42- 3.84 mg/dL
Which of the following statements best describes this patient's condition?
Q65
A 78-year-old male with history of coronary artery disease, status post coronary stent placement currently on aspirin and clopidogrel was found down in his bathroom by his wife. His GCS score was 3 and an accurate physical exam is limited. A stat non-contrast CT scan of his brain demonstrated a large right parietal intracranial hemorrhage with surrounding edema. He was promptly transferred to the intensive care unit (ICU) for monitoring. Over the next day, his mental status continues to worsen but repeat CT scan shows no new bleeding. In addition, the patient’s urinary output has been >200 cc/hr over the last several hours and increasing. His temperature is 99.0 deg F (37.2 deg C), blood pressure is 125/72 mmHg, pulse is 87/min, and respirations are 13/min. Which of the following values would most likely correspond to the patient’s urine specific gravity, urine osmolality, plasma osmolality, and serum sodium?
Q66
An 81-year-old man presents to his primary care physician for his yearly exam. His past medical history is significant for osteopenia, nephrolithiasis, and hypertension. His family history is significant for relatives who had early onset kidney failure. He takes occasional acetaminophen and supplemental calcium/vitamin D. He is physically active with a normal body mass index (BMI) and has no current concerns. Review of his laboratory results today were compared with those from 15 years ago with the following findings:
Results today:
Serum creatinine concentration: 1.1 mg/dL
Urine creatinine concentration: 100 mg/dL
Urine volume: 1000 mL/day
Results 15 years ago:
Serum creatinine concentration: 1.1 mg/dL
Urine creatinine concentration: 120 mg/dL
Urine volume: 1000 mL/day
Which is the most likely cause of these changes in his creatinine clearance?
Q67
A 28-year-old research assistant is brought to the emergency department for severe chemical burns 30 minutes after accidentally spilling hydrochloric acid on himself. The burns cover both hands and forearms. His temperature is 37°C (98.6°F), pulse is 112/min, respirations are 20/min, and blood pressure is 108/82 mm Hg. Initial stabilization and resuscitation is begun, including respiratory support, fluid resuscitation, and cardiovascular stabilization. The burned skin is irrigated with saline water to remove the chemical agent. Which of the following is the most appropriate method to verify adequate fluid infusion in this patient?
Q68
A 30-year-old woman is brought to the urgent care clinic by her husband. She complains of numbness around her lips and a tingling sensation in her hands and feet. She underwent near-total thyroidectomy for an enlarged thyroid gland a month ago. Vital signs include: blood pressure is 130/70 mm Hg, pulse is 72/min, respiratory rate is 16/min, and temperature is 37.0°C (98.6°F). A surgical incision scar is present in the anterior aspect of the neck. The attending physician inflates the blood pressure cuff above 150 mm Hg and observes the patient a couple of minutes while measuring her blood pressure. The patient develops sudden stiffness and tingling in her hand. Blood test results are as follows:
Hemoglobin (Hb%) 10.2 g/dL
White blood cell count 7000/mm3
Platelet count 160,000/mm3
Calcium, serum (Ca2+) 6.0 mg/dL
Albumin 4 g/dL
Alanine aminotransferase (ALT), serum 15 U/L
Aspartate aminotransferase (AST), serum 8 U/L
Serum creatinine 0.5 mg/dL
Urea 27 mg/dL
Sodium 137 mEq/L
Potassium 4.5 mEq/L
Magnesium 2.5 mEq/L
Urinalysis shows no white or red blood cells and leukocyte esterase is negative. Which of the following is the next best step in the management of this patient?
Renal US Medical PG Practice Questions and MCQs
Question 61: A 19-year-old male with cystic fibrosis is evaluated in the clinic for regular health maintenance. He is compliant with his respiratory therapy, but states that he often "forgets" to take the medications before he eats. A panel of labs is drawn which reveals a moderate vitamin D deficiency. Which of the following electrolyte abnormalities might be seen as a consequence of vitamin D deficiency?
A. Decreased calcium and increased phosphate
B. Decreased calcium and decreased phosphate (Correct Answer)
C. Increased calcium and increased phosphate
D. Increased calcium and decreased phosphate
E. Normal calcium and decreased phosphate
Explanation: **Decreased calcium and decreased phosphate**
- **Vitamin D deficiency** directly impairs calcium and phosphate absorption in the gut.
- In moderate or severe deficiency, **hypocalcemia** and **hypophosphatemia** result due to reduced GI absorption and impaired bone mineralization.
- This is the **classic electrolyte pattern** of vitamin D deficiency.
*Decreased calcium and increased phosphate*
- While **hypocalcemia** can be a direct result of vitamin D deficiency, **hyperphosphatemia** is not a typical consequence.
- **Increased phosphate** is more characteristic of conditions like kidney failure where phosphate excretion is impaired.
*Increased calcium and increased phosphate*
- **Hypercalcemia** and **hyperphosphatemia** are not associated with vitamin D deficiency.
- These levels are seen in conditions like excessive vitamin D supplementation/toxicity or certain malignancies.
*Increased calcium and decreased phosphate*
- **Hypercalcemia** is not a feature of vitamin D deficiency.
- This pattern is seen in **primary hyperparathyroidism**, where PTH mobilizes calcium from bone and kidneys while promoting phosphate excretion.
*Normal calcium and decreased phosphate*
- In **very early** vitamin D deficiency, compensatory PTH secretion might transiently maintain normal calcium while phosphate drops (PTH increases renal phosphate excretion).
- However, the question specifies **moderate vitamin D deficiency**, which would be severe enough to cause hypocalcemia despite PTH compensation.
- Both calcium and phosphate would be decreased at this stage.
Question 62: A 43-year-old woman is found in the hospital to have a plasma sodium concentration of 126 mg/dL. She was hospitalized after she expressed suicidal ideations and was started on a medication for major depressive disorder. Her past medical history is significant for diabetes for which she is currently taking metformin. Her blood pressure while in the hospital has been around 130/85 mmHg and she is not taking any other medications. Laboratory studies show a serum osmolality of 265 mOsm/kg. Which of the following best describes the cell bodies of the cells that are behaving abnormally in this patient?
A. Basophils in the anterior pituitary
B. Chromophobes in the anterior pituitary
C. Acidophils in the anterior pituitary
D. Located in the hypothalamus (Correct Answer)
E. Located in the posterior pituitary
Explanation: ***Located in the hypothalamus***
- The patient's **hyponatremia** (126 mg/dL) with a **low serum osmolality** (265 mOsm/kg) in the presence of depression and medication suggests **Syndrome of Inappropriate Antidiuretic Hormone (SIADH)**.
- **ADH (vasopressin)** is synthesized in the magnocellular neurosecretory cells of the **hypothalamus** (specifically the supraoptic and paraventricular nuclei) and then transported to the posterior pituitary for release. Since the patient's condition is due to inappropriate ADH secretion, the abnormality originates in the hypothalamus where these cells are located.
*Basophils in the anterior pituitary*
- **Basophils** in the anterior pituitary produce hormones like **TSH, FSH, and LH**, which are not directly involved in the regulation of water balance and sodium levels in the context of SIADH.
- An abnormality in these cells would lead to endocrine dysfunction related to thyroid or gonadal axes, not hyponatremia.
*Chromophobes in the anterior pituitary*
- **Chromophobes** are cells in the anterior pituitary that are typically undifferentiated or degranulated, often representing cells that have released their stored hormones.
- They are not primarily responsible for the production or release of hormones involved in water balance, so an abnormality here is unlikely to cause SIADH.
*Acidophils in the anterior pituitary*
- **Acidophils** in the anterior pituitary produce **growth hormone (GH)** and **prolactin**.
- Abnormalities in these cells would lead to conditions like acromegaly or hyperprolactinemia, neither of which explains the patient's hyponatremia and low serum osmolality.
*Located in the posterior pituitary*
- While the **posterior pituitary** stores and releases **ADH**, it does not synthesize it; the cell bodies responsible for ADH production are in the hypothalamus.
- Therefore, the primary abnormal cells in SIADH are the ones synthesizing ADH in the hypothalamus, not merely storing it in the posterior pituitary.
Question 63: A 35-year-old woman, gravida 2, para 1, at 16 weeks' gestation comes to the office for a prenatal visit. She reports increased urinary frequency but otherwise feels well. Pregnancy and delivery of her first child were uncomplicated. Her vital signs are within normal limits. Pelvic examination shows a uterus consistent in size with a 16-week gestation. Urinalysis shows mild glucosuria. Laboratory studies show a non-fasting serum glucose concentration of 110 mg/dL. Which of the following is the most likely explanation for this patient's glucosuria?
A. Decreased SGLT2 expression
B. Increased glomerular filtration barrier permeability
C. Decreased insulin production
D. Decreased insulin sensitivity
E. Increased glomerular filtration rate (Correct Answer)
Explanation: ***Increased glomerular filtration rate***
- During pregnancy, the **glomerular filtration rate (GFR)** significantly increases, leading to a higher filtered load of glucose.
- This increased load can exceed the reabsorptive capacity of the renal tubules, resulting in **glucosuria** despite normal blood glucose levels.
*Decreased SGLT2 expression*
- **SGLT2 inhibitors** are medications that decrease glucose reabsorption in the renal tubules, but there is no physiological decrease in SGLT2 expression during normal pregnancy that would cause glucosuria with normal blood glucose.
- SGLT2 expression itself is generally not altered in a way that leads to isolated glucosuria in healthy pregnancy.
*Increased glomerular filtration barrier permeability*
- Increased permeability of the **glomerular filtration barrier** would primarily lead to **proteinuria**, not glucosuria.
- Glucosuria implies glucose passing through the barrier normally but being uncleared by the tubules.
*Decreased insulin production*
- **Decreased insulin production** would lead to **hyperglycemia** in addition to glucosuria, which is not seen here as the non-fasting glucose is 110 mg/dL, well within the normal range.
- The patient's blood glucose is normal, ruling out significant insulin deficiency.
*Decreased insulin sensitivity*
- **Decreased insulin sensitivity** (insulin resistance) is a hallmark of gestational diabetes, but it would primarily cause **hyperglycemia**, which is not present in this patient (non-fasting glucose 110 mg/dL).
- While some insulin resistance occurs in pregnancy, it wouldn't cause glucosuria with normal blood glucose in the absence of other factors.
Question 64: A 68-year-old woman presents to her primary care physician for a regular check-up. She complains of swelling of her legs and face, which is worse in the morning and decreases during the day. She was diagnosed with type 2 diabetes mellitus a year ago and prescribed metformin, but she has not been compliant with it preferring 'natural remedies' over the medications. She does not have a history of cardiovascular disease or malignancy. Her vital signs are as follows: blood pressure measured on the right hand is 130/85 mm Hg, on the left hand, is 110/80 mm Hg, heart rate is 79/min, respiratory rate is 16/min, and the temperature is 36.6℃ (97.9°F). Physical examination reveals S1 accentuation best heard in the second intercostal space at the right sternal border. Facial and lower limbs edema are evident. The results of the laboratory tests are shown in the table below.
Fasting plasma glucose 164 mg/dL
HbA1c 10.4%
Total cholesterol 243.2 mg/dL
Triglycerides 194.7 mg/dL
Creatinine 1.8 mg/dL
Urea nitrogen 22.4 mg/dL
Ca2+ 9.6 mg/dL
PO42- 3.84 mg/dL
Which of the following statements best describes this patient's condition?
A. There is an error in Ca2+ measurement because the level of serum calcium is always decreased in the patient’s condition.
B. If measured in this patient, there would be an increased PTH level. (Correct Answer)
C. Increase in 1α, 25(OH)2D3 production is likely to contribute to alteration of the patient’s laboratory values.
D. The calcitriol level is unlikely to be affected in this patient.
E. Hypoparathyroidism is most likely the cause of the patient’s altered laboratory results.
Explanation: ***If measured in this patient, there would be an increased PTH level.***
- This patient presents with signs of **chronic kidney disease (CKD)**, indicated by **elevated creatinine (1.8 mg/dL)** and **urea nitrogen (22.4 mg/dL)**, along with edema.
- In CKD, the kidneys are less able to excrete phosphate and synthesize calcitriol (active vitamin D), leading to **hyperphosphatemia (PO42- 3.84 mg/dL)** and **hypocalcemia**. These imbalances stimulate the parathyroid glands to produce more **parathyroid hormone (PTH)** as a compensatory mechanism, a condition known as **secondary hyperparathyroidism**.
*There is an error in Ca2+ measurement because the level of serum calcium is always decreased in the patient's condition.*
- While **hypocalcemia** is common in CKD, it's not universally present, especially in early or moderate stages.
- The measured **calcium level (9.6 mg/dL)** is within the normal range, suggesting that the compensatory increase in **PTH** might be maintaining **normocalcemia** or that severe hypocalcemia has not yet developed.
*Increase in 1α, 25(OH)2D3 production is likely to contribute to alteration of the patient's laboratory values.*
- In CKD, there is a **decreased production of 1α,25(OH)2D3 (calcitriol)** by the kidneys, not an increase.
- The enzyme **1-alpha-hydroxylase**, responsible for converting 25-hydroxyvitamin D to active calcitriol, becomes deficient as renal function declines.
*The calcitriol level is unlikely to be affected in this patient.*
- The **calcitriol level is significantly affected in CKD**, specifically it is reduced.
- Reduced calcitriol synthesis is a key factor in the development of **secondary hyperparathyroidism** and **renal osteodystrophy**.
*Hypoparathyroidism is most likely the cause of the patient's altered laboratory results.*
- **Hypoparathyroidism** would lead to **low PTH levels**, typically resulting in **hypocalcemia** and **hyperphosphatemia** due to impaired renal phosphate excretion.
- This patient's presentation, particularly the high phosphate and normal calcium (suggesting compensation), is consistent with **hyperparathyroidism secondary to chronic kidney disease**, not hypoparathyroidism.
Question 65: A 78-year-old male with history of coronary artery disease, status post coronary stent placement currently on aspirin and clopidogrel was found down in his bathroom by his wife. His GCS score was 3 and an accurate physical exam is limited. A stat non-contrast CT scan of his brain demonstrated a large right parietal intracranial hemorrhage with surrounding edema. He was promptly transferred to the intensive care unit (ICU) for monitoring. Over the next day, his mental status continues to worsen but repeat CT scan shows no new bleeding. In addition, the patient’s urinary output has been >200 cc/hr over the last several hours and increasing. His temperature is 99.0 deg F (37.2 deg C), blood pressure is 125/72 mmHg, pulse is 87/min, and respirations are 13/min. Which of the following values would most likely correspond to the patient’s urine specific gravity, urine osmolality, plasma osmolality, and serum sodium?
A. Low, High, High, High
B. Low, Low, High, High (Correct Answer)
C. High, High, Low, Low
D. Low, Low, High, Low
E. High, Low, Low, High
Explanation: ***Low, Low, High, High***
- This patient's presentation, particularly the **large intracranial hemorrhage**, worsening mental status despite no new bleeding, and especially the **high urinary output (>200 cc/hr)**, is classic for **diabetes insipidus (DI)**, often neurogenic DI, due to damage to the posterior pituitary or hypothalamus.
- In DI, there is a deficiency of **ADH (vasopressin)**, leading to the kidneys' inability to reabsorb water. This results in the excretion of large volumes of **dilute urine** (low urine specific gravity, low urine osmolality) and concentration of the plasma (high plasma osmolality and hypernatremia, which means high serum sodium).
*Low, High, High, High*
- This pattern would indicate concentrated urine alongside concentrated plasma and high sodium, which contradicts the presence of **polyuria** and the underlying pathology of **diabetes insipidus (DI)**.
- High urine osmolality and specific gravity would suggest intact ADH function and water reabsorption in the kidneys, which is not what occurs in DI.
*High, High, Low, Low*
- This profile describes a state of **concentrated urine** but **dilute plasma** and **hyponatremia**, which is characteristic of the **Syndrome of Inappropriate Antidiuretic Hormone (SIADH)**.
- SIADH is the opposite of diabetes insipidus, involving excessive ADH leading to water retention, not excessive water excretion.
*Low, Low, High, Low*
- While **low urine specific gravity** and **low urine osmolality** are consistent with diabetes insipidus, a **low serum sodium** (hyponatremia) is not.
- In diabetes insipidus, the loss of free water typically leads to **hypernatremia** as the body becomes dehydrated.
*High, Low, Low, High*
- This combination is inconsistent with any common clinical scenario. A **high urine specific gravity** with a **low urine osmolality** is contradictory, as specific gravity is a measure of urine concentration, which correlates with osmolality.
- Furthermore, a **low plasma osmolality** with a **high serum sodium** is physiologically improbable.
Question 66: An 81-year-old man presents to his primary care physician for his yearly exam. His past medical history is significant for osteopenia, nephrolithiasis, and hypertension. His family history is significant for relatives who had early onset kidney failure. He takes occasional acetaminophen and supplemental calcium/vitamin D. He is physically active with a normal body mass index (BMI) and has no current concerns. Review of his laboratory results today were compared with those from 15 years ago with the following findings:
Results today:
Serum creatinine concentration: 1.1 mg/dL
Urine creatinine concentration: 100 mg/dL
Urine volume: 1000 mL/day
Results 15 years ago:
Serum creatinine concentration: 1.1 mg/dL
Urine creatinine concentration: 120 mg/dL
Urine volume: 1000 mL/day
Which is the most likely cause of these changes in his creatinine clearance?
A. Renovascular disease
B. Nephrolithiasis
C. Normal aging (Correct Answer)
D. Polycystic kidney disease
E. Benign prostatic hyperplasia
Explanation: ***Normal aging***
- As individuals **age**, there is a natural decline in **glomerular filtration rate (GFR)** due to nephron loss and sclerotic changes, even with a stable serum creatinine.
- The drop in **urine creatinine concentration** over 15 years, combined with a stable serum creatinine and urine volume, indicates a reduction in muscle mass and creatinine production, which is typical for an 81-year-old, thereby masking a decline in GFR.
*Renovascular disease*
- This typically causes a **drop in GFR** or **acute kidney injury**, often with a **rise in serum creatinine**.
- There is no increase in serum creatinine in this patient, and the presentation does not suggest **flash pulmonary edema** or **uncontrolled hypertension**.
*Nephrolithiasis*
- While the patient has a history of nephrolithiasis, it typically causes **acute, severe flank pain** or **obstructive kidney injury** when significant.
- There are no symptoms of acute obstruction, nor is there a significant increase in serum creatinine that would suggest a new stone causing obstruction.
*Polycystic kidney disease*
- This is a **genetic disorder** causing multiple cysts in the kidneys, leading to progressive kidney failure, often with a **family history of early-onset kidney failure**.
- While the family history is relevant, there are **no symptoms or physical exam findings** suggestive of PKD, such as kidney enlargement or hematuria.
*Benign prostatic hyperplasia*
- BPH can cause **obstructive uropathy** and a **rise in serum creatinine**, particularly if it leads to urinary retention.
- The patient has a normal urine volume and no symptoms of urinary obstruction such as **hesitancy, weak stream, or nocturia**.
Question 67: A 28-year-old research assistant is brought to the emergency department for severe chemical burns 30 minutes after accidentally spilling hydrochloric acid on himself. The burns cover both hands and forearms. His temperature is 37°C (98.6°F), pulse is 112/min, respirations are 20/min, and blood pressure is 108/82 mm Hg. Initial stabilization and resuscitation is begun, including respiratory support, fluid resuscitation, and cardiovascular stabilization. The burned skin is irrigated with saline water to remove the chemical agent. Which of the following is the most appropriate method to verify adequate fluid infusion in this patient?
A. The Parkland formula
B. Blood pressure
C. Pulmonary capillary wedge pressure
D. Heart rate
E. Urinary output (Correct Answer)
Explanation: ***Urinary output***
- Maintaining a specific **urinary output** (e.g., adult with major burns: 0.5-1.0 mL/kg/hr or 30-50 mL/hr) is the most reliable clinical indicator of adequate fluid resuscitation in burn patients.
- This ensures sufficient end-organ perfusion and avoids both under-resuscitation (leading to shock and organ damage) and over-resuscitation (risk of compartment syndrome and pulmonary edema).
*The Parkland formula*
- The **Parkland formula** is used to *calculate* the initial fluid volume needed, but it does not *verify* the adequacy of the infusion once started.
- This formula provides a starting point for fluid administration, which then needs to be adjusted based on the patient's response.
*Blood pressure*
- **Blood pressure** can be misleading in burn patients; it may remain deceptively normal due to compensatory mechanisms even with significant fluid deficits.
- It is a late indicator of hypovolemic shock, and relying solely on it can lead to under-resuscitation.
*Pulmonary capillary wedge pressure*
- **Pulmonary capillary wedge pressure (PCWP)** requires invasive monitoring via a pulmonary artery catheter, which is rarely indicated for routine fluid management in burn patients due to its invasiveness and associated risks.
- Less invasive and equally effective methods, like urinary output, are preferred for monitoring resuscitation.
*Heart rate*
- **Heart rate** is a sensitive but non-specific indicator of fluid status; it can be elevated due to pain, anxiety, or infection, not solely hypovolemia.
- While a decreasing heart rate can indicate improved fluid status, it is not as reliable or direct an indicator of end-organ perfusion as urinary output.
Question 68: A 30-year-old woman is brought to the urgent care clinic by her husband. She complains of numbness around her lips and a tingling sensation in her hands and feet. She underwent near-total thyroidectomy for an enlarged thyroid gland a month ago. Vital signs include: blood pressure is 130/70 mm Hg, pulse is 72/min, respiratory rate is 16/min, and temperature is 37.0°C (98.6°F). A surgical incision scar is present in the anterior aspect of the neck. The attending physician inflates the blood pressure cuff above 150 mm Hg and observes the patient a couple of minutes while measuring her blood pressure. The patient develops sudden stiffness and tingling in her hand. Blood test results are as follows:
Hemoglobin (Hb%) 10.2 g/dL
White blood cell count 7000/mm3
Platelet count 160,000/mm3
Calcium, serum (Ca2+) 6.0 mg/dL
Albumin 4 g/dL
Alanine aminotransferase (ALT), serum 15 U/L
Aspartate aminotransferase (AST), serum 8 U/L
Serum creatinine 0.5 mg/dL
Urea 27 mg/dL
Sodium 137 mEq/L
Potassium 4.5 mEq/L
Magnesium 2.5 mEq/L
Urinalysis shows no white or red blood cells and leukocyte esterase is negative. Which of the following is the next best step in the management of this patient?
A. 24-hour urinary calcium
B. Serum vitamin D level
C. CT scan abdomen with pancreatic protocol
D. Thyroid function tests
E. Serum parathyroid hormone (PTH) level (Correct Answer)
Explanation: ***Serum parathyroid hormone (PTH) level***
- The patient presents with **symptoms of hypocalcemia** (perioral numbness, tingling in hands and feet, positive Trousseau's sign, and serum calcium of 6.0 mg/dL) following a **near-total thyroidectomy**.
- Measuring **PTH levels** is crucial to determine if the hypocalcemia is due to **parathyroid gland damage** (low PTH) or another cause (high PTH).
*24-hour urinary calcium*
- This test is primarily used in the workup of **hypercalcemia** or **kidney stone disease** to assess calcium excretion.
- It is **not the initial diagnostic step** for symptomatic hypocalcemia post-thyroidectomy.
*Serum vitamin D level*
- While **vitamin D deficiency** can contribute to hypocalcemia, the acute onset of symptoms following thyroid surgery strongly points to parathyroid involvement.
- Addressing the **immediate calcium deficit** and evaluating PTH are higher priorities than measuring vitamin D levels at this stage.
*CT scan abdomen with pancreatic protocol*
- A CT scan of the abdomen with pancreatic protocol is used to evaluate **pancreatic pathology**, such as pancreatitis or tumors.
- This investigation is **irrelevant** to the patient's symptoms and recent thyroid surgery.
*Thyroid function tests*
- While important for managing patients post-thyroidectomy, routine thyroid function tests (TSH, T3, T4) are primarily to assess for **hypothyroidism** or **hyperthyroidism**.
- They do **not directly explain acute hypocalcemic symptoms** or guide immediate management of low calcium.
