I love a good algorithm. Evidence-backed decision trees and clear-cut clinical calculation tools help guide my practice as a nurse practitioner. They take the guesswork out of decision making so I can act with confidence, in the best interest of my patients. As I have become a more experienced NP, my toolkit of clinical decision making tools has expanded. Among my favorite go-to resources are two clinical calculators for detecting the likelihood of blood clots.
If you’re a nurse practitioner unfamiliar with Wells’ Criteria for DVT or the PERC Rule for Pulmonary Embolism, get acquainted. These two calculations make it easy for you to confidently rule out a clot, either a deep venous thrombosis (DVT) or pulmonary embolism (PE) in your patients. If you can’t rule out a clot, this signals you may need further testing to make your diagnosis. Here’s a quick rundown of these helpful tests.
Wells Criteria for DVT
The Wells Criteria comes in handy when you’ve got a patient with DVT symptoms. You know, swelling (usually unilateral) to a limb, pain, discoloration and/or warmth to the limb. Developed in 1995, Wells Criteria helps determine a patient’s probability of having a DVT. Answering a series of questions determines if DVT is a likely or unlikely diagnosis for your patient and guides the next steps in making a diagnosis or ruling out the condition. Patients unlikely to have a DVT based on their score may proceed to have the condition ruled out with lab work (D-dimer). Patients with a higher likelihood of DVT based on responses to Wells Criteria may need an ultrasound to rule out the condition.
The PERC rule is a useful tool for ruling out a pulmonary embolism (a blood clot in the lung). Patients with shortness of breath and chest pain (usually sharp, stabbing) and other PE symptoms are prime candidates for applying the PERC rule as there are a number of non-emergent problems that can also cause these symptoms. If none of the eight PERC criteria are present, you can rule out a pulmonary embolism in a patient who’s low risk. That means no further workup (for a PE, anyway) saving the time, risks and cost of imaging.
Remember, the PERC criteria can’t be applied to every patient you treat. The mnemonic HAD CLOTS helps recall which patients the PERC rule can’t be applied to:
Age > 50
DVT / PE history
O2 < 95%
Surgery / trauma < 28 days
You can see the specific PERC rule here as well as an outline for next steps depending on your patient’s score.
My favorite resource for making these clinical calculations quickly is MDCalc. The website is simple, easy to use, and contains basic background information and evidence for each test. Not to mention, you can simply input the parameters required by each calculation for your patient and the site will determine the clinical score for you. Don’t forget – it’s up to you as a nurse practitioner to decide if the clinical score applies to your patient and is the appropriate tool for ruling out the condition.