Differential Diagnosis

Based on the patient's laboratory results and allergy to doxycycline, the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis
  • Urinary Tract Infection (UTI): The elevated leukocyte count and low urobilinogen suggest a possible infection. The acidic urine pH and high specific gravity also support this diagnosis, as they can indicate concentrated urine, which is common in UTIs. Given the patient's age and symptoms, a UTI is a common and likely diagnosis.
• Other Likely Diagnoses
  • Pyelonephritis: This is an infection of the kidney, which could explain the elevated leukocyte count and low urobilinogen. The patient's symptoms and laboratory results could be consistent with pyelonephritis, especially if the UTI has ascended to the kidneys.
  • Dehydration: The high specific gravity of the urine suggests dehydration, which could be a contributing factor to the patient's symptoms. Dehydration can also cause a concentrated urine, leading to an acidic pH.
• Do Not Miss Diagnoses
  • Sepsis: Although less likely, sepsis is a life-threatening condition that requires immediate attention. The elevated leukocyte count could be indicative of a systemic infection, and it is crucial to rule out sepsis, especially in a patient with a potential infection.
  • Kidney Stones: Kidney stones can cause severe pain, nausea, and vomiting, and can also lead to a UTI. The patient's symptoms and laboratory results could be consistent with kidney stones, and it is essential to consider this diagnosis to avoid missing a potentially serious condition.
• Rare Diagnoses
  • Interstitial Nephritis: This is a rare condition characterized by inflammation of the kidney tissue. The patient's symptoms and laboratory results could be consistent with interstitial nephritis, although it is less likely.
  • Glomerulonephritis: This is a rare condition characterized by inflammation of the glomeruli, the filtering units of the kidney. The patient's symptoms and laboratory results could be consistent with glomerulonephritis, although it is less likely.

Given the patient's allergy to doxycycline, alternative antibiotic recommendations for a UTI or pyelonephritis could include:

• Trimethoprim-sulfamethoxazole
• Ciprofloxacin
• Amoxicillin-clavulanate
• Cefixime

It is essential to note that the patient's age (15 years old) and allergy to doxycycline should be taken into consideration when selecting an antibiotic. A healthcare professional should be consulted to determine the best course of treatment.