Final answer:
In patients with a low probability of PE based on the Wells criteria, the D-dimer test is most helpful in ruling out the condition due to its high negative predictive value when negative.
Step-by-step explanation:
The laboratory study most helpful in ruling out a pulmonary embolism (PE) in patients with a low probability based on the Wells criteria is the D-dimer test. The D-dimer is a fibrin degradation product that is typically elevated in the presence of a significant clot or thrombus because it is released when a blood clot is broken down in the body. A low or normal D-dimer level can be used to rule out PE with a high degree of certainty in patients who are judged to be low-risk by clinical assessment tools such as the Wells score.
However, a high D-dimer level is not definitive for PE, as it can be elevated in various conditions, including infection, inflammation, trauma, or recent surgery. Therefore, the D-dimer test is most valuable when it is negative, which has a high negative predictive value for PE in a low-risk patient.
The lab study that is most helpful in ruling out a PE (pulmonary embolism) in a patient with a low probability based on the Wells criteria is a D-dimer test.
D-dimer is a blood test that measures a substance released when a blood clot breaks up. If the D-dimer level is low, it indicates a low likelihood of a PE.
It is important to note that a negative D-dimer test cannot completely rule out a PE, and further imaging tests may be necessary to confirm the absence of a PE.