calcium,phosphate and magnesium metabolism
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Time limit: 10 minutes
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Question 1
Multiple choiceA 63-year-old male presents with chronic kidney disease. Laboratory analysis reveals a serum calcium level of 1.8 mmol/L (normal range: 2.2–2.6), phosphate level of 2.0 mmol/L (normal range: 0.8–1.4), and elevated parathyroid hormone (PTH) levels. Given the clinical picture, what is the most likely cause of his hypocalcemia?
Explanation
The hypocalcemia in a patient with chronic kidney disease is primarily due to impaired renal excretion of calcium, as the kidneys are unable to adequately filter and reabsorb calcium. Increased phosphate retention can contribute to secondary hyperparathyroidism, but it is the renal failure that directly accounts for the hypocalcemia.
Question 2
Multiple choiceA 45-year-old woman with a history of hyperthyroidism presents with symptoms of muscle weakness and fatigue. Laboratory tests indicate hypercalcemia (total calcium 3.2 mmol/L) and low phosphorus levels. What is the most appropriate next step in management?
Explanation
The hypercalcemia is likely due to increased bone turnover from hyperthyroidism. Proper management involves controlling the hyperthyroidism, which should lead to normalization of calcium levels. Vitamin D supplementation is inappropriate as it could worsen hypercalcemia.
Question 3
Multiple choiceA 50-year-old woman with chronic alcoholism presents with confusion, muscle cramps, and fatigue. Laboratory results show calcium level 1.9 mmol/L, magnesium 0.5 mmol/L, and phosphate 0.7 mmol/L. Which aspect of her laboratory findings most significantly impacts her neuromuscular function?
Explanation
The low magnesium level is critical as magnesium is essential for neuromuscular transmission. Its deficiency can lead to neuromuscular excitability, explaining the confusion and muscle cramps. Calcium and phosphate levels, while also relevant, do not explain her acute neuromuscular symptoms as clearly as magnesium does.
Question 4
Multiple choiceA 32-year-old man presents with muscle cramps, laryngeal spasms, and paresthesias of the hands. His total calcium level is normal at 2.4 mmol/L, but ionized calcium is critically low. What laboratory test would most likely help clarify the cause of his symptoms?
Explanation
Measuring the serum albumin will clarify whether the low ionized calcium is due to low protein levels affecting the total calcium count, as only the ionized calcium level represents the biologically active form. Normal total calcium does not rule out hypocalcemia from low albumin.
Question 5
Multiple choiceA 70-year-old female diagnosed with osteoporosis presents with a recent hip fracture after a minor fall. Her lab results show high levels of serum ALP and urinary NTx. Which factor most significantly influences her current clinical situation?
Explanation
Increased ALP and NTx levels indicate heightened osteoclastic activity, which is driving bone resorption leading to bone loss. This increases the risk for fractures in osteoporotic patients. Other factors like renal function or diet may contribute but are not the primary drivers in this scenario.
Question 6
Multiple choiceA 75-year-old man with a history of prolonged PPIs presents with chronic fatigue, muscle weakness, and numbness of the extremities. Serum analysis confirms hypomagnesemia. What is the most effective management strategy for this patient?
Explanation
Starting magnesium supplementation is critical to correct the hypomagnesemia and alleviate the symptoms. PPIs are known to cause magnesium malabsorption; therefore, while long-term management could include addressing PPI use, immediate supplementation is necessary.
Question 7
Multiple choiceA 55-year-old female is treated for chronic renal failure. She exhibits signs of hypocalcemia, and lab tests reveal elevated PTH levels and low serum calcium. Which factor is most likely contributing to her condition?
Explanation
In chronic renal failure, the kidneys are unable to produce sufficient calcitriol (active vitamin D), leading to reduced intestinal absorption of calcium and low serum calcium levels. This in turn stimulates PTH secretion as a compensatory mechanism.
Question 8
Multiple choiceA 30-year-old female who recently underwent gastric bypass surgery is found to have osteopenia. Her biochemical profile shows low vitamin D and calcium levels. What is the best course of action for managing her osteopenia?
Explanation
Providing vitamin D and calcium supplementation is critical for improving her mineral status post-surgery, as gastric bypass can limit nutrient absorption. Bisphosphonates are not first-line treatment without further assessment of bone density.
Question 9
Multiple choiceA 62-year-old man with multiple myeloma presents to the emergency room with severe back pain and weakness. His lab results indicate hypercalcemia, renal impairment, and low albumin levels. What likely underlying mechanism is contributing to his hypercalcemia?
Explanation
The hypercalcemia in this scenario is primarily driven by the osteolytic lesions associated with multiple myeloma, leading to increased bone resorption and subsequent release of calcium into the bloodstream, rather than through dietary intake or renal route.
Question 10
Multiple choiceA 65-year-old male patient presents to the emergency department with symptoms of muscle weakness, nausea, and confusion. His medical history includes chronic renal failure and prolonged use of a loop diuretic. Laboratory tests show elevated serum calcium levels at 3.2 mmol/L (normal range 2.20–2.60) and decreased serum phosphate at 0.5 mmol/L (normal range 0.8–1.4). Given this information, what is the most likely explanation for his current clinical status?
Explanation
The patient's renal failure is the primary factor leading to impaired calcium excretion, resulting in hypercalcemia. The use of a loop diuretic may exacerbate the imbalance, leading to additional electrolyte disturbances, such as hypophosphatemia. Other options do not effectively explain the combination of hypercalcemia and hypophosphatemia in this context.