Differential Diagnosis for Flank Pain, RBC, and Protein in Urine

The patient's presentation of flank pain, red blood cells (RBC), and protein in the urine, with negative findings for crystals on microscopy and a negative bacterial culture, suggests several potential diagnoses. These can be categorized as follows:

• Single Most Likely Diagnosis

  • Nephrolothiasis (Kidney Stones): Although the microscopy was negative for crystals, kidney stones can still be present, especially if they are not actively shedding crystals at the time of the test or if the stone is made of a material not typically visible under microscopy (e.g., certain types of drug stones). The presence of flank pain and hematuria (RBC in urine) are classic symptoms for nephrolothiasis.

• Other Likely Diagnoses

  • Glomerulonephritis: This condition involves inflammation of the glomeruli, the filtering units of the kidneys, and can present with hematuria and proteinuria. The absence of bacterial infection and crystals does not rule out glomerulonephritis, as it can be caused by various factors, including autoimmune diseases, infections, and vasculitis.
  • Pyelonephritis: Although the bacterial culture is negative, it's possible that the infection was not caught at the right time or that the patient has been partially treated, leading to a false-negative culture. Chronic pyelonephritis can cause scarring and potentially lead to symptoms similar to those presented.
  • Interstitial Nephritis: This condition involves inflammation of the spaces around the renal tubules and can be caused by drugs, infections, or systemic diseases. It may present with flank pain, hematuria, and proteinuria.

• Do Not Miss Diagnoses

  • Renal Cell Carcinoma: Although less common, renal cell carcinoma can present with hematuria and flank pain. It's crucial to consider this diagnosis to avoid missing a potentially life-threatening condition.
  • Vasculitis (e.g., ANCA-associated vasculitis): Conditions like granulomatosis with polyangiitis (formerly known as Wegener's granulomatosis) can cause renal symptoms, including hematuria and proteinuria, along with systemic symptoms. Missing this diagnosis could lead to significant morbidity and mortality.
  • Renal Infarction: This is a rare but potentially life-threatening condition where the blood supply to the kidney is interrupted, leading to tissue death. It can present with acute flank pain and hematuria.

• Rare Diagnoses

  • Loin Pain-Hematuria Syndrome: A rare condition characterized by recurrent episodes of severe flank pain and hematuria, often without an identifiable cause. It's considered when other diagnoses have been ruled out.
  • Nutcracker Phenomenon: A rare condition where the left renal vein is compressed between the aorta and the superior mesenteric artery, leading to hematuria and flank pain. It's more common in younger individuals and those with a thin body habitus.
  • Renal Artery Aneurysm or Arteriovenous Malformation: These vascular abnormalities can cause hematuria and flank pain due to the abnormal blood flow within the kidney. They are rare and often require specific imaging studies for diagnosis.