Long Covid continues to evade clear diagnostic testing, as researchers from the National Institute of Health's RECOVER Initiative revealed in a study published in the Annals of Internal Medicine.

Despite examining data from over 10,000 patients across 83 clinical sites, the study found no significant differences in routine lab results between those suffering from long Covid and those without the condition.

This outcome underscores the challenges in diagnosing Long Covid, a condition estimated to affect around 17 million Americans.

The study diagnosed Long Covid based on a scoring system of 12 symptoms, including brain fog, dizziness, and palpitations, without requiring a positive Covid test.

This approach, while thorough, has left some experts questioning its effectiveness.

Dr. Marc Sala, a pulmonologist and co-director of the Comprehensive COVID Center at Northwestern Medicine, acknowledged the study's merits but also pointed out its limitations.

In an NBC News report, Sala argued that routine tests might not be sufficient to uncover novel causes of Long COVID-19 and that more specialized tests, such as those conducted during exercise or following COVID-19 pneumonia, might be necessary.

The researchers said after propensity score adjustment, participants with prior infection had a lower mean platelet count than participants without known prior infection, as well as higher mean hemoglobin A1c (HbA1c) level (5.58%) vs. 5.46% and urinary albumin–creatinine ratio (81.9 mg/g) vs. (43.0 mg/g).

Although differences were of modest clinical significance. The difference in HbA1c levels was attenuated after participants with preexisting diabetes were excluded.

Among participants with prior infection, no meaningful differences in mean laboratory values were found between those with a post-acute sequelae of SARS-CoV-2 infection (PASC) index of 12 or higher and those with a PASC index of zero.

Researchers note that laboratory tests might detect persistent organ damage in individuals with minimal or no symptoms. Although studies have identified potential biomarkers related to Post-Acute Sequelae of SARS-CoV-2 (PASC), the results have been inconsistent, likely due to variations in study definitions, biomarkers used, comparison groups, symptom duration, types of symptoms, and patient demographics.

Autoimmune, hormonal, viral, and other biomarkers linked to PASC phenotypes have been reported, but small sample sizes, inadequate follow-up, and lack of proper controls have limited many studies.

Additionally, early small-cohort studies did not find routine clinical biomarkers, and there is a shortage of large-scale research on the effectiveness of standardized lab tests in clinical care.

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