Nephrolithiasis (Kidney Stones): This condition is characterized by the formation of stones in the kidneys, which can cause severe pain (often referred to as colic) and hematuria (blood in the urine). The pain typically starts in the flank area (costovertebral angle tenderness) and can radiate to the groin. The presence of blood in the urine supports this diagnosis, as stones can cause microscopic or gross hematuria.

Pyelonephritis: An infection of the kidney, which can cause flank pain, fever, and hematuria. The costovertebral angle tenderness is a classic sign of pyelonephritis.
Urinary Tract Infection (UTI): While more commonly associated with lower urinary tract symptoms, an upper UTI can cause flank pain and hematuria.
Glomerulonephritis: An inflammation of the glomeruli, the filtering units of the kidneys, which can cause hematuria and flank pain.

Renal Cell Carcinoma: Although less common, it's crucial not to miss this diagnosis. Hematuria can be a presenting symptom, and flank pain can occur if the tumor grows large enough to cause discomfort or if it metastasizes.
Renal Infarction: A condition where the blood supply to the kidney is interrupted, leading to tissue death. It can cause severe flank pain and hematuria. This is a medical emergency.
Aortic Aneurysm or Dissection: While not directly related to the urinary system, a ruptured abdominal aortic aneurysm or dissection can cause flank pain and, if it involves the renal arteries, can lead to hematuria. This is a life-threatening condition.

Renal Trauma: Direct injury to the kidney can cause hematuria and flank pain. This would typically be associated with a history of trauma.
Vasculitis: Certain types of vasculitis, such as ANCA-associated vasculitis, can affect the kidneys and cause hematuria and flank pain.
Tuberculosis of the Kidney: A rare condition in many parts of the world, which can cause chronic flank pain and hematuria.