The Fagan’s nomogram is widely recognised as a convenient graphical calculator and is frequently referenced in evidence-based medicine and clinically . the LR for the test result that may be used, will point to the post-test probability of disease. Adapted from Fagan TJ. Nomogram for. Bayes’s theorem N Engl J Med . Two-step Fagan Nomogram. A Graphical Tool to Interpret a Diagnostic Test Result Without Calculation. What’s a nomogram? A nomogram is a.

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You also need to know the likelihood ratio for the diagnostic test. View December 4, The point of intersection is the new estimate of the probability that your patient has this disease.

Suppose one of our patients is a boy with no special risk factors. Learn more about this tracker and how you need to take action.

The EU Trials Tracker: In this blog, Giorgio Karam examines the evidence on antihypertensive drugs for primary prevention — when do we start treatment? View March 8, Here are details on how the graph works and how you could construct a similar graph yourself.

File:Fagan – Wikimedia Commons

This version requires the Shockwave plug-in. When you extend this line to the right, it intersects nomobram the post-test probability of disease. Subscribe to our newsletter You will receive our monthly newsletter and free access to Trip Premium. Nomoggram is usually related to the prevalence of the disease, though this may be modified up or down on the basis of certain risk factors that are present nomogrxm your patient pool or possibly in this particular patient.

You can also browse for pages similar to this one at Category: Fagan inis a useful paper-only tool in the practice of evidence-based medicine. In one way, this method will confirm the diagnosis and will give the physician a good standpoint from which to start the indicated treatment.


In the case of medicine, a radiography or CT with contrast medium is more expensive and carries a higher risk for the patient than an ultrasound nonogram example. The two-step Fagan nomogram takes a step back, incorporating lines for test sensitivity and specificty, which are used to directly determine the Likelihood Ratios.

File:Fagan nomogram.svg

First, the computations involved use odds rather than ratios. Therefore, in the absence of a broad existence of evidence-based tools for determining the pre-test probability of many diseases, clinicians may end up making an estimate based on their existing knowledge and observations. What are the key steps in EBM? But how is it estimated? View March 9, These figures are often more widely known than the LRs derived from them. What can we say about the chances that this boy will develop hip dysplasia?

In order to elucidate this method in a simple manner we will review this example in an emergency department setting: View April 9, Suppose a LR in 4 for a positive test in diagnosing a disease. The diagnostic test is positive. A web based version of the Fagan Nomogram is available at www. The Fagan nomogram is a graphical tool for estimating how much the result on a diagnostic test changes the probability that a patient has a disease NEJM ; Is it possible to achieve a good probability to diagnose a disease with the safer test available?

If you multiply the pre-test odds by the likelihood ratio, you will get the post-test odds. EBM at the bedside: In this case, there are some simple methods the physician can use to obtain some evidence to support his decision-making.


One way to interpret and analyze a diagnostic test is by using likelihood ratios LRwhich are basically a ratio of the probability that a result is correct to the probability that the result is incorrect.

Obtaining the pre-test probability is the first step of this method. In moderate risk patient points the odds of PE are To answer this question I would like to address an example: You draw a line connecting the pre-test probability of disease and the nonogram ratio.

After conducting a primary examination the physician suspects an episode of fwgan embolism PE. To use this tool, you need to provide your best estimate of the probability of the disease prior to testing.

Write labels in terms of probabilities rather than odds. The intuitive concept of a LR is this. With the prevalence of To illustrate how likelihood ratios work, let me take the example of a year-old male with a positive stress nomohram exam used in patients with suspected coronary artery disease.

ragan Therefore, the odds of this patient having PE is around A picture of the Fagan nomogram appears below. As you can see in the image, this tool is composed of seven criteria with scores that range from 1. The likelihood of this patient having a disease has increased by approximately six-fold given the positive test result. Here are a couple examples of how to use the Fagan nomogram. The results of the score are 6.