Jeff Kline Answers Your Clotting Questions

Pulmonary embolism testing hinges on pretest probability, and D-dimer becomes far less specific in COVID. Pregnancy, PERC nuance, and newer D-dimer strategies all change how clinicians can safely avoid over-imaging while still respecting missed-clot risk.

COVID, PE, and D-dimer

• Poor specificity in COVID: A normal D-dimer still helps exclude PE, but in COVID the standard threshold has only about 15% specificity, making positive results common and often unhelpful.
• CT over reflex dimer: In sick COVID patients with real concern for pulmonary embolism, CT pulmonary angiography is the more useful test because D-dimer can stay markedly elevated for weeks without a visible macro clot.
• Ambulatory versus admitted risk: Discharged ambulatory COVID patients do not appear to need extra PE testing or routine anticoagulation simply because of COVID, while admitted patients carry substantially higher thromboembolic risk.
• Early clotting signal: Thrombotic risk seems to rise early, around the onset of myalgias, but how long that risk persists after acute illness is less certain. We get into the practical timing uncertainty in the episode.
• PERC in COVID: Available reports suggest PERC still performs if every criterion is met, with the oxygen saturation cutoff doing important work in COVID patients.

PERC nuance and new cutoffs

• Highest heart rate counts: For PERC, the official answer is to use the highest recorded heart rate, so a transient tachycardia at triage still makes the patient PERC positive.
• YEARS-guided dimer strategy: Low-risk patients who are PERC positive can sometimes use a higher D-dimer threshold when the YEARS score is zero, a shift that reduces imaging without losing safety. We walk through that pairing in the chapter.
• Which clots get missed: The main PEs below the higher D-dimer threshold are typically subsegmental or chronic clots, not the larger obstructive events most clinicians are trying to catch.
• Why 500 is low: The classic 500 ng/mL cutoff is framed as overly conservative, reflecting a push for near-perfect sensitivity rather than the clinically meaningful clots that drive outcomes.
• Gestalt decision domains: Kline breaks PE suspicion into five elements: knowledge, present data, visual impression, pattern recognition, and normative behavior, giving gestalt a more explicit structure.

Pregnancy PE evaluation and practice

• Normal dimer still helps: A normal D-dimer can support stopping the PE workup in pregnancy across any trimester, rather than treating pregnancy itself as a reason to ignore the test.
• Pregnancy-adapted thresholds: Pregnancy-adjusted D-dimer strategies can safely raise the cutoff in selected low-pretest-probability patients, while keeping a lower threshold when YEARS features are present.
• Bedside leg ultrasound role: For pregnant patients with an intermediate D-dimer result, bedside venous ultrasound for DVT can clarify the workup before moving straight to chest imaging.
• Austere setting bridge therapy: When transfer delays make PE workup impractical, a single dose of low molecular weight heparin or rivaroxaban may be reasonable if there are no contraindications.
• Documenting considered PE: If PE crossed your mind but you chose not to test, document that you considered it and why it was unlikely; that charting distinction is worth hearing in the podcast.

References:

1. Kline JA, et al. Multicenter registry of United States emergency department patients tested for SARS-CoV-2. J Am Coll Emerg Physicians Open. 2020 Nov 12;1(6):1341-1348. PMID: 33392542.
2. Freund Y, et al. Effect of a Diagnostic Strategy Using an Elevated and Age-Adjusted D-Dimer Threshold on Thromboembolic Events in Emergency Department Patients With Suspected Pulmonary Embolism: A Randomized Clinical Trial. JAMA. 2021 Dec 7;326(21):2141-2149. PMID: 34874418.
3. van der Pol LM, et al; Artemis Study Investigators. Pregnancy-Adapted YEARS Algorithm for Diagnosis of Suspected Pulmonary Embolism. N Engl J Med. 2019 Mar 21;380(12):1139-1149. PMID: 30893534.
4. ATTACC Investigators; ACTIV-4a Investigators; REMAP-CAP Investigators, Lawler PR, et al. Therapeutic Anticoagulation with Heparin in Noncritically Ill Patients with Covid-19. N Engl J Med. 2021 Aug 26;385(9):790-802. PMID: 34351721.
5. Elberts SJ, et al. The impact of COVID-19 on the sensitivity of D-dimer for pulmonary embolism. Acad Emerg Med. 2021 Oct;28(10):1142-1149. PMID: 34425044.