Quiz 14

A 69 year old male patient suddenly becomes short of breath 3 days after surgical repair of a femoral hip fracture. His EKG shows sinus tachycardia. There is no sign of ischemia. He undergoes a test to detect if he has had a pulmonary embolus. The sensitivity of the test is 90% and the specificity of the test is 90% against the gold standard test.

Q1. What is the positive predictive value of the test?

1. 98%
2. 90%
3. 85%
4. 50%
5. More information is required to say this

Answer is Choice 5. With the given info, positive predictive value of the test cannot be calculated. To calculate either the positive or the negative predictive value of the test, one has to have not only the sensitivity and specificity of the test in question but also the prevalence of the disease in the population being tested.

Q2. The test comes back as positive (High probability).What is the most appropriate next step?

1. Start IV (Intravenous) heparin
2. Start IV heparin and oral Warfarin
3. Place an IVC (Inferior vena cava) filter
4. Do a pulmonary angiogram
5. Repeat the test in 2-3 days

Answer is Choice 1. The next step is IV heparin alone until you establish that the APTT is in therapeutic range. Although in Britain I used to start Heparin and Warfarin at the same time, it is not the standard of care in the USA. This is based on the fact that the first vitamin K dependant factors affected by Warfarin are Factors C & S. These natural anticoagulants , once affected , lead to a pro-coagulant state. They should not be targeted until heparin has laid down an anti-coagulant affect.