Differential Diagnosis for Positive CRP Test
A positive CRP (C-reactive protein) test indicates inflammation in the body. The differential diagnosis can be broad, given the nonspecific nature of CRP elevation. Here's a categorized approach to differential diagnoses:
- Single Most Likely Diagnosis
- Bacterial Infection: This is often the first consideration due to the body's acute phase response to bacterial infections, which typically causes a significant rise in CRP levels. Common examples include pneumonia, urinary tract infections, and sepsis.
- Other Likely Diagnoses
- Viral Infections: While CRP levels may not rise as high as in bacterial infections, certain viral infections, especially those causing significant tissue damage or systemic illness (like COVID-19), can lead to elevated CRP.
- Autoimmune Diseases: Conditions such as rheumatoid arthritis, lupus, and inflammatory bowel disease can cause chronic elevation of CRP due to ongoing inflammation.
- Trauma or Surgery: Significant tissue injury from trauma or surgery can lead to an acute phase response, elevating CRP levels.
- Do Not Miss Diagnoses
- Sepsis: Although mentioned under bacterial infections, sepsis is a critical diagnosis that must not be missed due to its high mortality rate if not promptly treated.
- Malignancy: Certain cancers can cause chronic inflammation, leading to elevated CRP levels. While not the most common cause, missing a diagnosis of cancer can have severe consequences.
- Giant Cell Arteritis/Polymyalgia Rheumatica: These conditions can present with elevated CRP and require prompt treatment to prevent complications like vision loss.
- Rare Diagnoses
- Familial Mediterranean Fever: A genetic disorder that causes recurrent episodes of fever and inflammation, leading to elevated CRP during episodes.
- Hyper-IgD Syndrome: A rare condition characterized by recurrent episodes of fever and inflammation, with elevated IgD levels and CRP during episodes.
- Castleman Disease: A rare disorder that involves an overgrowth of cells in the body's lymph nodes, which can lead to elevated CRP among other symptoms.
Each of these diagnoses has a different set of clinical presentations, histories, and additional diagnostic tests that can help narrow down the cause of a positive CRP test. Clinical judgment, combined with a thorough patient history and physical examination, is crucial for guiding further diagnostic workup and management.