Finding | Increased Disease Probability (Positive Likelihood Ratio) |
---|---|

Positive proximal CUS, complete CUS, or color flow duplex US | 12.1 |

Note: accuracy of ultrasound is operator-dependent. Reported LRs may not be reproducible by an inexperienced sonographer. LR+ reported as a range and listed here as upper limit for the purposes of this interactive tool (see below for detail). |

Finding | Decreased Disease Probability (Negative Likelihood Ratio) |
---|---|

Negative proximal CUS, complete CUS, or color flow duplex US | 0.03 |

Note: accuracy of ultrasound is operator-dependent. Reported LRs may not be reproducible by an inexperienced sonographer. LR- reported as a range and listed here as upper limit for the purposes of this interactive tool (see below for detail). |

**Narrative:** This was a small systematic review (n = 201) that evaluated the utility of emergency department (ED) performed ocular ultrasound. A total of 3 studies were included in the final analysis and overall the data was low risk for bias. Operating characteristics were not pooled. Among the 3 studies included, there was not a clear definition for a positive test result. In one of the included studies, no positive test definition was provided. These results should be interpreted with caution given the small number of patients included and the operator dependent nature of this POCUS exam. A more recent study with larger variability in operator experience suggests the all-comer sensitivity may be much lower.

**Caveats:** Note: accuracy of ultrasound is operator-dependent. Reported LRs may not be reproducible by an inexperienced sonographer.

*Published in collaboration with The POCUS Atlas*

**Author:** Matthew Riscinti, MD

**Published/Updated:** September 13, 2018

LR, pretest probability and posttest (or posterior) probability are daunting terms that describe simple concepts that we all intuitively understand.

Let's start with pretest probability: that's just a fancy term for my initial impression, before we perform whatever test it is that we're going to use.

For example, a patient with prior stents comes in sweating and clutching his chest in agony, I have a pretty high suspicion that he's having an MI – let's say, 60%. That is my pretest probability.

He immediately gets an ECG (known here as the "test") showing an obvious STEMI.

Now, I know there are some STEMI mimics, so I'm not quite 100%, but based on my experience I'm 99.5% sure that he's having an MI right now. This is my posttest probability - the new impression I have that the patient has the disease after we did our test.

And likelihood ration? That's just the name for the statistical tool that converted the pretest probability to the posttest probability - it's just a mathematical description of the strength of that test.

Using an online calculator, that means the LR+ that got me from 60% to 99.5% is 145, which is about as high an LR you can get (and the actual LR for an emergency physician who thinks an ECG shows an obvious STEMI).

(*Thank you to Seth Trueger, MD for this explanation!*)