Research Tracker›Biomarker Atlas›Long COVID›Cystatin D (CST5)

Cystatin D (CST5) in Long COVID

Cystatin D (CST5), also described as Protease inhibitor, belongs to the inflammatory group of Long COVID (PASC, Post-Acute Sequelae of COVID-19) markers and is reported to be raised relative to Non-COVID controls. Symptom domains tied to this marker in the source include elevated at 6 months post-infection. This entry summarises Kallaste et al. 2025. Group-level associations like this do not translate into an individual diagnostic cut-off.

↑ ElevatedInflammatory

Summary

Direction in Long COVID↑ Elevated — higher than in the comparison group
CategoryInflammatory
Also described asProtease inhibitor
Compared againstNon-COVID controls
Associated symptomsElevated at 6 months post-infection
Test typeBlood test (serum / plasma / whole blood)
SourceKallaste et al. 2025 — doi:10.3390/medicina61060996
Condition atlasLong COVID Biomarker Atlas

Related Inflammatory markers in Long COVID

Full list: Long COVID Biomarker Atlas.

Frequently asked questions

Is Cystatin D (CST5) high or low in Long COVID?

Elevated. Studies summarised in the OSMF atlas report higher Cystatin D (CST5) in Long COVID than in Non-COVID controls. Source: Kallaste et al. 2025.

What symptoms is Cystatin D (CST5) associated with in Long COVID?

The cited literature associates this marker with Elevated at 6 months post-infection. These are population-level associations and do not mean the marker causes the symptoms.

Which test measures Cystatin D (CST5)?

It is measured as a blood test (serum / plasma / whole blood). Many of the cited studies used research-grade assays, so clinical availability may vary.

Is one abnormal Cystatin D (CST5) result diagnostic of Long COVID?

No. No single biomarker is diagnostic of Long COVID. Cystatin D (CST5) findings come from group comparisons, overlap considerably between patients and controls, and vary with study design, timing and comparison group. A result should be interpreted by a clinician alongside symptoms, history and other tests.

Cite this page

Open Source Medicine Foundation. (2026). Cystatin D (CST5) in Long COVID: direction, evidence and what it means. OSMF Research Tracker. Retrieved October 7, 2026, from https://research.opensourcemed.info/biomarkers/long-covid/cystatin-d-cst5.html
Get OSMF research updates. New biomarker, trial and treatment evidence summaries by email.
Subscribe on Substack

Last reviewed: 2026-06-29 · Page generated from long-covid.json · Browse: Long COVID atlas · Biomarker Index · All marker pages

Disclaimer: This page is an educational synthesis of published, peer-reviewed research and is not medical advice. Biomarker findings vary across studies with case definitions, comparison groups, timing and assay methods. Direction of change reflects the predominant finding in the cited source and does not establish a diagnostic threshold. Discuss any test result with a qualified clinician.