Hypertension: A DBP of 100 is above the normal range, suggesting hypertension as the most likely diagnosis. This is a common condition that can be primary (essential) or secondary to other factors such as kidney disease, sleep apnea, or certain medications.

White Coat Hypertension: This condition is characterized by elevated blood pressure readings in a clinical setting but normal readings at home. It could be a factor if the DBP of 100 is consistently observed only in a medical environment.
Anxiety or Stress: Temporary elevations in blood pressure can occur due to anxiety or stress, which might explain a DBP of 100 in certain situations.
Pregnancy-Induced Hypertension: In pregnant women, a DBP of 100 could indicate pregnancy-induced hypertension, a condition that requires close monitoring.

Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodic or sustained hypertension. Although unlikely, missing this diagnosis could be fatal due to the risk of hypertensive crises.
Renal Artery Stenosis: Narrowing of the arteries that supply blood to the kidneys, which can lead to secondary hypertension. This condition is important not to miss because it may require specific intervention.
Hyperthyroidism: An overactive thyroid gland can cause increased blood pressure. While not the most common cause of hypertension, it's a condition that needs to be identified and treated appropriately.

Cushing's Syndrome: A rare endocrine disorder caused by excess cortisol, which can lead to hypertension among other symptoms.
Hyperaldosteronism: A condition characterized by the overproduction of aldosterone, leading to hypertension and hypokalemia (low potassium levels).
Coarctation of the Aorta: A congenital condition where the aorta is narrowed, which can cause high blood pressure, particularly in younger individuals.