While the majority of patients fully recover from COVID-19, a significant number experience long-term health consequences. A study of 273,618 COVID-19 survivors published in PLOS medicine1 has revealed that one out of three patients has shown clinical features of long COVID even three up to six months after their COVID-19 diagnosis.
The NICE guideline on long COVID2 defines long COVID syndrome as symptoms that develop during or following an infection with COVID-19 and continue for more than 12 weeks. The full clinical picture of long COVID is complex and far from being understood. It comprises a constellation of heterogeneous symptoms with unclear cause and uncertain direct association with SARS-CoV-2 infection.
More than 50 long-term symptoms have been documented3; the most frequent ones are fatigue, anosmia and dyspnea, headaches, and attention deficit. Factors like female sex, older age, active smoking or a severe, acute illness are associated with a higher risk to develop “long COVID”.
Currently, no laboratory test definitively distinguishes long COVID conditions from other etiologies, partly due to the heterogeneity of post COVID conditions. In the follow-up of recovered patients with post-acute consequences, clinical tests provide reliable support to identify the causes of ongoing symptoms and, most importantly, rule out serious diseases. In patients with ongoing symptoms, a basic panel of laboratory tests should be taken into consideration, which include tests for comorbidities that may contribute to the disease.
Guidelines recommend assessing a basic panel including electrolytes, renal and liver function tests, transaminases CRP and Ferritin in all long COVID patients. A study4 has revealed that more than a quarter of patients having recovered from COVID-19, have shown elevated D‑dimer levels up to four months after diagnosis. Since elevated D-dimer levels increase the long-term risk for a thromboembolic disease, it is recommended to observe this marker during post COVID monitoring in justified cases as well.
1. Taquet M, Dercon Q, Luciano S, Geddes JR, Husain M, et al. (2021) Incidence, co- occurrence, and evolution of long-COVID features: A 6-month retrospective cohort study of 273,618 survivors of COVID-19. PLOS Medicine 18(9): e1003773. https://doi.org/10.1371/journal.pmed.1003773
2. National Institute for Health and Care Excellence, Royal College of General Practitioners, Healthcare Improvement Scotland SIGN. COVID-19 rapid guideline: managing the long term effects of COVID-19. 2020. www.nice.org.uk/guidance/ng188.
3. Lopez-Leon, S., Wegman-Ostrosky, T., Perelman, C. et al. More than 50 long-term effects of COVID-19: a systematic review and meta-analysis. Sci Rep 11, 16144 (2021). https://doi.org/10.1038/s41598-021-95565-8
4. Townsend L, Fogarty H, Dyer A, et al. Prolonged elevation of D-dimer levels in convalescent COVID-19 patients is independent of the acute phase response. J Thromb Haemost. 2021;19:1064–1070. https://doi.org/10.1111/jth.15267