Normal variant: A calcium level of 8.4 is within the normal range (typically 8.5-10.5 mg/dL, but can vary slightly by lab) for most adults, suggesting that this value may not indicate any underlying pathology.

Dehydration: Can cause a mild elevation in calcium levels due to hemoconcentration.
Mild hyperparathyroidism: Early or mild cases might not significantly elevate calcium levels above the normal range but could still be present with levels at the higher end of normal.
Vitamin D deficiency: Although more commonly associated with low calcium, some cases might have a compensatory mechanism keeping calcium levels in the normal range.

Hyperparathyroidism: Even though the calcium level is at the lower end of normal or slightly below, hyperparathyroidism, especially primary hyperparathyroidism, needs to be considered due to its potential for significant morbidity if left untreated.
Malignancy: Certain cancers, like multiple myeloma or other lymphoproliferative disorders, can lead to hypercalcemia, but early stages might not significantly elevate calcium levels.
Vitamin D intoxication: Although less common, it can lead to hypercalcemia and has serious implications.

Familial hypocalciuric hypercalcemia (FHH): A rare genetic disorder that affects calcium metabolism, leading to mild hypercalcemia.
Lithium-induced hypercalcemia: Patients on long-term lithium therapy can develop hyperparathyroidism or have altered calcium homeostasis.
Thyroid disease: Both hyperthyroidism and hypothyroidism can affect calcium levels, though this is less common and usually associated with other clinical findings.