Increases in PTH are often accompanied by hypophosphatemia.

In addition, serum creatinine should be measured to assess renal function; hypercalcemia may impair renal function, and renal clearance of PTH may be altered depending on the fragments detected by the assay.

 

 

Content 3

Content 13

A 70-year-old woman is brought to the emergency department with right flank pain, nausea, vomiting, and blood in her urine. She has no fever. She has recurrent kidney stones, vague abdominal pain, muscle weakness, and atrophy.

On examination, she is in moderate distress secondary to her flank pain. Other than right back pain, her physical examination is normal. Urinalysis reveals large amounts of blood but no signs of infection. An intravenous pyelogram (IVP) is performed and reveals numerous kidney stones. A metabolic panel shows an extremely elevated calcium level. Further workup demonstrates that the patient has hyperparathyroidism from a parathyroid adenoma.

Summary: A 70-year-old woman who presents to the emergency department with kidney stones, abdominal pain, and muscle weakness is found to have hyperparathyroidism.

Questions

How does parathyroid hormone (PTH) increase intestinal calcium absorption?

  • PTH Increases absorption by increasing the production of 1,25-dihydroxycholecalciferol (1 α-hydroxylase activity is increased).

What effect do elevated levels of PTH have on renal phosphate reabsorption?

What are three factors that increase the activity of 1 α-hydroxylase in the kidney?

Answers to Case 38: Calcium Metabolism

 

  •  

  • Elevated levels of PTH and effect on phosphate: Inhibits renal phosphate reabsorption in proximal tubule, resulting in phosphate excretion.

  • Three factors that increase 1 α-hydroxylase activity: Increased PTH, decreased serum calcium and phosphate levels.

Clinical Correlation

Hypercalcemia can be caused by a variety of conditions, including those which increase calcium absorption (milk-alkali syndrome), decrease calcium excretion (thiazide use), increase mobilization of the bone (hyperparathyroidism), and involve metastatic cancer (breast, prostate, etc.). A patient's symptoms depend on the level of hypercalcemia. With a mild elevation, a patient may be asymptomatic. With increasing levels, patients may have constipation, anorexia, nausea, vomiting, abdominal pain, nephrolithiasis, renal failure, emotional lability, confusion, psychosis, or coma.

 

Question 1 of 10

A 43-year-old male is admitted to the emergency room for severe pain in his left flank, radiating to the groin. The pain is intermittent and initiated after running a marathon on a hot summer day. The patient is asked for a urine specimen and blood is detected in the urine. He is hydrated, and additional diagnostic procedures are done. Laboratory values show serum Ca2+of 12 mg/dL, and PTH values of 130 pg/mL. Which of the following findings would be predictable in this patient?

The correct answer is B.

The precipitating factor in this young otherwise healthy patient is dehydration. He has high parathyroid hormone (PTH) levels (probably a problem that had been ongoing). High PTH is associated with increased bone resorption resulting in increased serum calcium (and consequently filtered calcium), which with dehydration, precipitated and formed kidney stones (reason for the pain and the blood in the urine when he passed them). You would expect low serum inorganic phosphate (Pi) because PTH promotes Pi excretion. High PTH would stimulate vitamin D synthesis and thus intestinal calcium absorption. The urinary calcium excretion likely reflects a reabsorption process that has been overwhelmed by the excess calcium filtered. The increase in bone resorption and turnover would be expected to be associated with increased serum alkaline phosphatase.

 


 

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