The C-reactive protein (CRP) test is a blood test that measures the level of CRP in your blood, which can be an indicator of inflammation in the body. While not a specific test for tuberculosis (TB), it can help in excluding a TB diagnosis under certain conditions, which is described below.
How the CRP test relates to TB
-
Not a direct diagnostic tool: CRP is an inflammation marker that can be elevated due to many conditions, not just TB. Therefore, it can not confirm a TB diagnosis on its own.
-
Excluding TB: According to the reference, a very low CRP level can help rule out TB. Specifically, a CRP level of less than 1.5 mg/L could reliably exclude a diagnosis of TB. However, this only applies to a relatively small percentage of people being screened.
-
Thresholds and predictive value: The reference shows that the negative predictive value of the CRP test for TB increases as the CRP threshold decreases:
CRP Threshold (mg/L) Negative Predictive Value for TB ≥50 91.1% ≥1.5 100%
Key takeaways:
- CRP alone can not diagnose TB: High CRP levels indicate inflammation, which could be due to many causes.
- Low CRP may rule out TB: A CRP level of below 1.5 mg/L indicates a very low probability of TB, according to the provided reference.
- Clinical judgment is crucial: CRP levels need to be interpreted within the context of other symptoms, test results, and patient history.
