Differential Diagnosis for Elevated CRP with Mild Fever, Flank Pain, and Urinalysis Findings
Single Most Likely Diagnosis
- Pyelonephritis: This condition is characterized by an infection of the kidney, which could explain the flank pain, mild fever, elevated CRP, and the presence of blood and trace leukocytes in the urine. The absence of nitrates does not rule out this diagnosis, as not all urinary tract infections (UTIs) produce positive nitrate tests.
Other Likely Diagnoses
- Nephrolithiasis (Kidney Stones): The presence of flank pain and blood in the urine (hematuria) are classic symptoms for kidney stones. While kidney stones may not directly cause an elevated CRP, the associated pain and possible infection could lead to an inflammatory response.
- Urinary Tract Infection (UTI) with Involvement of the Lower Urinary Tract: Although the primary symptoms suggest upper urinary tract involvement, a UTI limited to the lower urinary tract (e.g., cystitis) could also present with similar findings, especially if there's an associated inflammatory response.
Do Not Miss Diagnoses
- Sepsis from a Urinary Source: Although less likely given the mild presentation, any infection in the urinary tract has the potential to 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, leading to tissue death. It can present with acute flank pain and might be associated with an elevated CRP due to the inflammatory response to tissue necrosis.
Rare Diagnoses
- Renal Cell Carcinoma: While rare, certain types of kidney cancer could present with hematuria and flank pain. An elevated CRP could be seen in the context of a paraneoplastic syndrome or if the tumor causes an obstructive infection.
- Vasculitis Involving the Kidneys (e.g., ANCA-associated vasculitis): These are autoimmune conditions that can affect the kidneys and present with a wide range of symptoms, including flank pain, hematuria, and elevated inflammatory markers like CRP.
- Xanthogranulomatous Pyelonephritis: A rare form of chronic pyelonephritis that can present with flank pain, hematuria, and systemic symptoms like fever, often associated with a long-standing urinary tract obstruction and infection.