Dyspnea Due to Heart Failure (With Chronic Respiratory Disease)

Diagnostics and Likelihood Ratios, Explained

Positive Findings (Patient Has This)

Risk FactorsIncreased Disease Probability (Positive Likelihood Ratio)
History of Atrial fibrillation4.1× (2.5-6.6)
History of Coronary artery bypass grafting2.8× (1.3-5.8)
History of Myocardial infarction2.2× (1.4-3.5)
History of Diabetes mellitus2.0× (1.3-3.2)
History of Coronary artery disease2.0× (1.5-2.6)
History of Angina1.7× (1.0-2.5)
History of Hypertension1.2× (0.95-1.5)
SymptomsIncreased Disease Probability (Positive Likelihood Ratio)
Orthopnea1.3× (1.1-1.5)
Fatigue1.1× (0.96-1.3)
Nocturnal cough0.93× (0.73-1.2)
SignsIncreased Disease Probability (Positive Likelihood Ratio)
3rd heart sound (ventricullar filling gallop)57.0× (7.6-425)
JVD4.3× (2.8-6.5)
Lower extremity edema2.7× (2.2-3.5)
Rales2.6× (2.1-3.3)
Hepatic congestion2.4× (1.2-4.7)
Enlarged heart1.6× (0.43-6.2)
Wheezing0.85× (0.65-1.1)
OtherIncreased Disease Probability (Positive Likelihood Ratio)
Clinician's Gestalt9.9× (5.3-18)
CXR FindingsIncreased Disease Probability (Positive Likelihood Ratio)
Edema11.0× (5.8-22.0)
Cardiolmegaly7.1× (4.5-11.0)
Pleural effusion(s)4.6× (2.6-8.0)
Pneumonia1.0× (0.46-2.3)
Hyperventilation0.53× (0.25-1.1)
Normal0.11× (0.04-0.28)
EKG FindingsIncreased Disease Probability (Positive Likelihood Ratio)
Atrial fibrillation6.0× (3.4-10.0)
Ischemic ST-T waves4.6× (2.4-8.7)
Q waves3.1× (1.8-5.5)
BNP LevelsIncreased Disease Probability (Positive Likelihood Ratio)
BNP ≥100 pg/ml4.1 (3.3-5.0)

Negative Findings (Patient Doesn't Have This)

Risk FactorsDecreased Disease Probability (Negative Likelihood Ratio)
Coronary artery disease0.67× (0.54-0.84)
Atrial fibrillation0.74× (0.63-0.85)
Myocardial infarction0.84× (0.74-0.96)
Hypertension0.84× (0.65-1.1)
Diabetes mellitus0.85× (0.74-0.97)
Angina0.90× (0.80-1.0)
Coronary artery bypass grafting0.92× (0.84-0.99)
SymptomsDecreased Disease Probability (Negative Likelihood Ratio)
Orthopnea0.68× (0.48-0.95)
Fatigue0.79× (0.54-1.2)
Nocturnal cough1.1× (0.85-1.4)
SignsDecreased Disease Probability (Negative Likelihood Ratio)
Rales0.39× (0.28-0.55)
Lower extremity edema0.41× (0.30-0.57)
JVD0.65× (0.54-0.78)
3rd heart sound (ventricullar filling gallop)0.83× (0.75-0.91)
Hepatic congestion0.91× (0.84-1.0)
Enlarged heart0.99× (0.95-1.0)
Wheezing1.2× (0.94-1.4)
OtherDecreased Disease Probability (Negative Likelihood Ratio)
Clinician's Gestalt0.65× (0.55-0.77)
CXR FindingsDecreased Disease Probability (Negative Likelihood Ratio)
Cardiolmegaly0.54× (0.44-0.67)
Edema0.68× (0.58-0.79)
Pleural effusion(s)0.78× (0.69-0.89)
Pneumonia1.0× (0.93-1.1)
Hyperventilation1.1× (1.0-1.2)
EKG FindingsDecreased Disease Probability (Negative Likelihood Ratio)
Atrial fibrillation0.73× (0.63-0.84)
Ischemic ST-T waves0.83× (0.74-0.93)
Q waves0.84× (0.75-0.94)
BNP LevelsDecreased Disease Probability (Negative Likelihood Ratio)
BNP ≥100 pg/ml0.09× (0.04-0.19)


A low BNP might be helpful in ruling out CHF if the pre-test probability is equivocal. However, if pretest probability for CHF is low and BNP is above threshhold, BNP would not be helpful in ruling in CHF. In other words, very low BNP values in patients with low probability of heart failure and very high BNP values in patients with high probability of the disease can confirm clinical suspicions.



Khaled Hassan, MD and Shahriar Zehtabchi, MD


April 8, 2013

What are Likelihood Ratios?

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!)