Urokinase-type plasminogen activator soluble receptor (suPAR) assay in clinical routine: evaluation one year after its introduction in the high automation corelab of the A. Gemelli hospital

To the Editor,

Medical laboratories undergo a continuous quality improvement process to increase efficiency and customer satisfaction and answer and meet clinical requests.

It is an ongoing process that evaluates how an organization can improve its processes, to guarantee the best possible healthcare, to deliver the right test to the right patient prompting the right action and to reduce overall healthcare costs [1].

The critical role of laboratory medicine in SARS-CoV-2 pandemic extends far more than the etiological diagnosis of COVID-19 [2]. Biochemical monitoring of COVID-19 patients through biomarkers has become critical for assessing disease severity and progression, monitoring therapeutic intervention as well as making treatment decisions using a precision medicine approach [3].

Literature data from the last two years has shown increasing interest towards the relationship between soluble urokinase-type plasminogen activator receptor (suPAR) concentration and clinical severity and/or mortality in patients with SARS-CoV-2 infection [4] and the SAVE-MORE trial showed how an early treatment with Anakinra guided by suPAR levels (suPAR≥6 ng mL), in patients hospitalized with moderate and severe SARS-CoV-2 infection, significantly reduced the risk of worse clinical outcome [5, 6].

suPAR is the soluble circulating, and therefore easily measurable form of uPAR and is present on immunologically active cells but also on endothelial cells, keratinocytes, fibroblasts, smooth muscle cells, megakaryocytes, certain tumor cells, kidney podocytes and is considered one of the strongest biomarkers of innate immunity activation [7].

Several studies have documented that high suPAR levels has been observed in several conditions, including aging, sepsis, bacterial and viral infection, chronic inflammation, chronic renal injury chronic liver disease, diabetes, certain types of cancer and consistently associates with mortality in septic patients in intensive care units [8, 9].

Moreover, it seems to robustly predict all cause mortality both cardiovascular and non-cardiovascular in patients with chronic heart failure and in hemodialysis patients [10].

During the fight against COVID 19 disease, in our Polyclinic A. Gemelli laboratory, several routine and novel biomarkers have been used to identify patients at higher risk of developing severe diseases and to ensure the safe and quick discharge of patients who will not develop severe and fatal forms.

Among these novel biomarkers, the suPAR assay was introduced in March 2021 in our High Automation Corelab (the first clinical routine customer in Italy and one of the study sites from the SAVE-MORE clinical trial) to answer and meet the infectious disease specialist requests, with the objective of identifying COVID-19 patients to be treated in early stages with Anakinra.

SuPAR is one of the relatively few biomarkers that has evolved from laboratory investigations into routine clinical use, but the technology for using suPAR in clinical routine has hampered its implementation.

The first commercially available dosages were ELISA methods (suPARnostic^® ViroGates or Human uPAR R&D systems), then a lateral flow assay for point-of-care use (suPARnostic^® Quick Triage, ViroGates) was produced.

Only recently a turbidimetric assay was available on commercial platform, allowing suPAR to be analyzed with a short turnaround time at highly automated laboratories with fast, robust, repeatability and accurate and precise determination, therefore ensuring a higher analytical quality and a wider application of the assay in clinical practice [11].

Since the suPAR implementation in our routine laboratory workflow, we have observed a progressive increase in clinical requests despite the COVID 19 hospitalization decrease; we then thought to analyze the number of suPAR tests performed in our Corelab, differentiated by department and patient pathologies, to evaluate the impact of the suPAR introduction on clinicians and in non-COVID 19 areas.

From 13.04.2021 to 13.05.2022, we performed 2,532 suPAR assays in plasma samples anticoagulated with EDTA, using a turbidimetric immunoassay (suPARnostic^® TurbiLatex, ViroGates A/S, Copenhagen, Denmark). The kit was applied according to the manufacturer’s instructions on Advia XPT analyzer (Siemens Healthcare Diagnostics, USA), with lower limit of quantification of 1.7 ng/mL and upper limit of quantification of 26.5 ng/mL.

The CV intra-assay and inter-assay at 3.2 ng/mL level, were 3.5 and 11%, respectively.

The total number of patients was 2,350 (males 65%; mean age 68 ± 23 y) and COVID19 positive ones were 70%. The 88% of the dosages (n. 2,225) showed values above the clinical cut-off of 3.0 ng/mL, in particular 930 were between 3 and 5.9 ng/mL (mean and median: 4.4 ng/mL, 25–75P: 3.7–5.1 ng/mL) and 1,295 were higher than 6 ng/mL (mean: 11.7 ng/mL, median: 9.5 ng/mL and 25–75P: 7.5–13.6 ng/mL) while 307 dosages were below the cut off of 3 ng/mL (mean and median: 2.4 ng/mL, 25–75P: 2.2–2.7 ng/mL).

In the 8 months of 2021, 1,296 tests were performed, while in the first 5 months of 2022 an increase of 40% was observed (1,236 tests). In 2021 the requests from COVID departments were 66.5%, from the Department of Emergency and Acceptance (DEA) 16.5% and from various units (Medicine, Surgery, Intensive care) 17%; in 2022 requests for COVID19 patients confirmed the levels of 2021 (67.6%), while those from DEA decreased to 7.4% and those from other units increased up to 25%.

We analyzed the diagnoses of all patients, using in-hospital Laboratory Information System. If, in 2021, the requests were almost all from COVID 19 patients, including those from the DEA, in 2022 there was a progressive expansion of the clinical reasons.

SuPAR test was required in cardiological, haematological, nephrological and hemodialyzed patients, in critically ill patients with suspected sepsis or Acute Coronary Syndrome, mainly for risk stratification in several clinical settings, not exclusively infectious.

Because of the routine availability of the test and supported by the evidence from the scientific literature on suPAR clinical utility, clinicians began to use and appreciate the suPAR, in a variety of conditions beyond the COVID 19 disease.

Therefore, the suPAR test introduced during the SARS Cov 2 pandemic to answer to infectious disease specialists request, is progressively becoming a predictive and independent biomarker for our clinicians, to evaluate the patient outcome in diversified areas, to improve the diagnostic accuracy, to guide therapeutic decisions and to safely and quickly distinguish between high-risk acute patients who will require admission to hospitals and low-risk patients who can be discharged. Therefore, the suPAR assay implementation in clinical routine workflow seems to support healthcare professionals in making clinical decisions and improve patient management and outcome.