Differential Diagnosis for Left Back Pain, Increased Urination, and Abnormal Urinalysis

Single Most Likely Diagnosis

• Pyelonephritis: This condition, an infection of the kidney, is suggested by the combination of left back pain (which could indicate involvement of the left kidney), increased urination, and the presence of small leukocytes and trace blood in the urinalysis. These symptoms are classic for a urinary tract infection that has ascended to the kidney.

Other Likely Diagnoses

• Nephrolithiasis (Kidney Stones): The presence of back pain and trace blood in the urine could indicate kidney stones, especially if the stones are causing obstruction or irritation leading to increased urination and possibly infection (suggested by leukocytes).
• Urinary Tract Infection (UTI) - Lower: While the back pain might suggest an upper urinary tract infection, it's possible that a lower UTI (cystitis) could cause similar symptoms, especially if the infection is severe or if there's associated ureteral irritation.
• Prostatitis: In males, prostatitis could cause increased urination frequency, pain, and potentially some back pain, along with abnormal urinalysis findings.

Do Not Miss Diagnoses

• Sepsis from a Urinary Source: Although less likely, any urinary tract infection can potentially lead to sepsis, a life-threatening condition. Early recognition and treatment are crucial.
• Renal Infarction: This is a rare but serious condition where the blood supply to the kidney is interrupted, potentially causing severe back pain and changes in urination. It would be a critical diagnosis not to miss.
• Pyclonephritis with Obstruction: If a kidney stone or other obstruction is present along with pyelonephritis, it could lead to severe consequences, including sepsis or loss of kidney function.

Rare Diagnoses

• Renal Cell Carcinoma: Although rare, kidney cancer could potentially cause back pain, changes in urination, and blood in the urine. It would be an important diagnosis to consider, especially in older adults or those with risk factors.
• Interstitial Nephritis: This condition, often caused by medications or infections, could lead to similar symptoms, including pain and changes in urination, but is less common than other diagnoses listed here.
• Vascular Conditions (e.g., Renal Artery Aneurysm or Vasculitis): These are rare conditions that could potentially cause back pain and changes in urination but would be less likely without other specific symptoms or risk factors.