How Accurate Is The Probe To Bone Test In Diagnosing Osteomyelitis?
A new meta-analysis in Clinical Infectious Diseases notes that the commonly used probe to bone test can accurately rule in diabetic foot osteomyelitis in high-risk patients and rule out osteomyelitis in patients at low risk for the bone infection.1 Based on seven studies that met the inclusion criteria, Lam and colleagues found pooled sensitivity and specificity for the probe to bone test to be 0.87 and 0.83 respectively.
What matters in testing for osteomyelitis is pre-test probability. This is based on Bayes’ theorem.2 Therefore, the location of where the test happens is important. In the case of probe to bone, if someone is in the hospital where the probability of having osteomyelitis is very high, then the likelihood of a probe to bone test being accurate is high. If, however, one is in an outpatient center where the probability of osteomyelitis is lower (like one in five), then this is a less accurate test.
However, you can use that to your advantage. You can say if the probe to bone test is negative on an outpatient, you can rely on it, and if it is positive on an inpatient, you can rely on it. That is the essence of this excellent meta-analysis.
References
1. Lam K, Van Asten SA, Nguyen T, et al. Diagnostic accuracy of probe to bone to detect osteomyelitis in the diabetic foot: a systematic review. Clin Infect Dis. 2016; epub July 1.
2. Boone K. Bayesian statistics for dummies. Available at https://www.kevinboone.net/bayes.html .
