Another great study resource. It is important to interpret the D-dimer in relation to the Wells PE score. A low risk PE based on Wells score should be investigated with a D dimer (ie low Wells score and negative D-dimer rule out a PE). However, if the patient has a high Wells score (>4) then there is a risk of false negatives with the D dimer - therefore it is recommended that these patient go straight to have a CTPA without a D dimer. Check with your local hospital guidelines for exact cut off values. Age adjusted D-dimers and the use of the PERC score are also interesting discussion points and can help decision making in clinical practice.