The perks of PERC

The really worrying question sometimes arises (or depending on your luck, most times arises) while you are in an ED, and you see a patient who comes in with ‘some chest pain’ that’s maybe a little pleuritic in nature, but pleuritic chest pain could result from a punch to the chest, or if you cough too hard or too long (I unfortunately speak from experience!) and you don’t know what to do and someone’s already done a D-Dimer on the patient’s initial bloods as they were triaged, before you saw them, if you are lucky enough to work in a department as great as ours (or unlucky, depending on how you view the over-testing of D-Dimers!) – I have been handed the most amazing tool: the PERC score, or the Pulmonary Embolism Rule-out Criteria. For those of you already aware of the existence of such a magic wand – bravissimo and kudos to you, and no need to read on any further. For the ones like me who until very recently hadn’t even heard of it, please proceed further.

Patients who present with clinically low risk for development of a PE can be subjected to the PERC. This is a pre-test probability type situation, whereby you assess a patient based on clinical parameters (which you obviously already do!) but you mentally check them off a list of specific parameters, and if they meet all 8 (yes EIGHT!) criteria, then you can safely say they do not need further assessment RE:pulmonary embolism, D-dimers, CTPA route etc. This creates a warm and fuzzy feeling in me, because almost every patient in the past 3 years of practising emergency medicine in the UK that presents even remotely with pleuritic sounding chest pain, regardless of whether they have a clinical indication or not, automatically had a D-dimer, and, God forbid, should they have an ever-so-slightly-raised D-dimer level, they were referred to the acute medical team faster than you could say enoxaparin. These were then possibly unnecesarily given doses of enoxaparin, until the gold standard rule-out test could be performed, which is the CT PA (CT pulmonary angiography). That’s just the way things worked, because a positive D-dimer can indicated possible pulmonary embolism, but it needs to be taken with the complete clinical picture, and a (very large) grain of salt. D-dimers can, unfortunately or fortunately, be raised in a number of different situations, e.g an underlying active malignancy (which gives the double whammy of raising your chances of getting a PE in the first place), an infection anywhere in the body, certain medications and inflammatory medical conditions. ┬áThis lead to over treatment of many patients with anticoagulants till the CTPA was performed to finally confirm the existence or absence of the offending clot. Things may have changed for the better with the PERC, though.

The parameters you base your PERC score on are Age (< 50 years), O2 sats (greater than or equal to 95%), Heart Rate (less than 100 BPM), Absence of Hemoptysis, Absence of Oestrogen usage (Contraceptive pills), Absence of history of surgery/trauma requiring hospitalisation/immobilisation within past 4 weeks, Absence of lower limb swelling (unilateral), and absence of prior personal history of clots/emboli/thrombi.

These parameters and this score are widely used now and available as calculator/apps on most phones.

So the way I understand is, low-risk patients meeting the PERC score criteria need not be further assessed (even if they have had a D-dimer done that’s slightly raised, you can ignore it because the pre-test probability was extremely low). Low-risk patients not meeting the PERC criteria may then go on to be assessed on the D-dimer route, and the high risk patients go directly to CTPA without faffing around with PERCs and WELLS and GENEVAs.

Good luck, and happy PERC-ing!