Hypercalcemia and Hypocalcemia

Primary Causes of Calcium and Parathyroid Disorders

• The most common cause of hypocalcemia is primary hypoparathyroidism.

• The second most common cause of hypercalcemia is malignancy.

• There are various forms of hypoparathyroidism that contribute to calcium levels, which require detailed discussion.

Malignancy and Bone Metastasis

• Cancers with an affinity for direct bone metastasis, specifically those exhibiting a tendency toward lytic mats, are a common cause of hypercalcemia.

• Increased lytic activity due to bone metastasis results in the release of calcium and phosphorus into the bloodstream.

• Key Ectopic Mechanisms:

  • Ectopic production of a $PTH$-like substance by certain cancers.

  • Ectopic production of the active form of $\text{Vitamin } D_3$ by specific cancers, which leads to hypercalcemia.

• Multiple Myeloma:

  • This condition increases osteoclast activity, leading to alterations in serum calcium.

Clinical Evaluation and Sequential Diagnostic Steps

• Drug interactions are a frequent source of hypocalcemia, with $\text{Vitamin } D$ toxicity being the most common specific cause.

• Step-by-Step Rule of Thumb for Elevated Calcium:

  1. Inquire about $\text{Vitamin } D$ intake.

  2. Rule out artifactual causes such as venous status during the blood draw; this may necessitate a retest.

  3. If results are confirmed normal and the patient is retested, measure the peak of the parathyroid hormone ($PTH$) to identify potential primary hyperparathyroid situations.

• Associated Signs of Malignancy:

  • Clinical findings such as anemia, inflammation, and other related lab results typically accompany malignancy-related calcium issues.

Artifactual Hypercalcemia and Albumin Binding

• Artifact hypercalcemia is very common and is usually the cause of borderline or slight elevations in calcium findings.

• Slight elevations warrant a retest to rule out errors.

• Causes of Artifacts:

  • Venous status.

  • Hyper pro anemia: This refers to elevated albumin levels. Since calcium binds to albumin, higher protein levels increase the amount of bound calcium, making it appear as though hypercalcemia is present.

The CHIMPS Mnemonic for Hypercalcemia

• The mnemonic CHIMPS is used to recall the primary causes of hypercalcemia:

  • C: Cancers.

  • H: Hypothyroidism.

  • I: I at eugenic (such as excessive $\text{Vitamin } D$ administration or specific drug interactions).

  • M: Multiple Myeloma. This involves the secretion of an active, classic activating factor, resulting in either diffuse osteopenia or multiple punched out lytic lesions.

  • P: Primary. Specifically primary hypoparathyroidism.

  • S: Sarcoidosis.

Causes of Calcium Imbalance and Lab Errors

• Lab errors can lead to a diagnosis of hypercalcemia.

• Hypo pro anemia is a common cause, specifically hypo albumin anemia (hypoalbuminemia) involving the calcium bound to albumin.

• This is frequently the most common cause of hypercalcemia.

• Hypo albumin IMU typically stems from malabsorption or malnutrition.

Chronic Renal Failure and Calcium Absorption

• Chronic renal failure is categorized as the second most common cause of hypercalcemia.

• Mechanism:

  • The final activation of $\text{Vitamin } D_3$ does not occur in the kidneys.

  • The absence of active $\text{Vitamin } D_3$ leads to a decrease in the absorption of calcium from the gut.

Post-Surgical Hypoparathyroidism and Vitamin D Deficiency

• Post-Surgical Hypoparathyroidism:

  • Occurs following a complete thyroidectomy if the small parathyroid glands are lost or impacted by disease.

  • Results in a decreased level of $PTH$, leading directly to hypercalcemia.

• Vitamin D Deficiency:

  • This deficiency causes osteo Malaysia in adults and rickets in children.

  • These are malnutrition diseases characterized by decreased $\text{Vitamin } D$ intake.

  • This leads to a decrease in calcium absorption from the gut, which ultimately results in hypercalcemia.