Journal of veterinary internal medicine2026; 40(5); aalag207; doi: 10.1093/jvimsj/aalag207

Thymidine kinase 1 activity in serum and body cavity fluids of horses with lymphoma.

Drozdzewska, K
·
Burde, S
·
Müller, E
·
Merle, R
·
Gehlen, H

Abstract: The accuracy of serum thymidine kinase 1 (TK1S) as a biomarker of lymphoma in horses is variable. The value of measurement in body cavity fluid (TK1F) has not been established. Objective: (1) TK1F and TK1S will be higher in horses with lymphoma compared to diseased controls (DCs); (2) TK1F will be higher than TK1S; and (3) there will be a strong correlation between both measurements. Methods: Twenty animals in the lymphoma and 31 animals with nonneoplastic, gastrointestinal/respiratory disorders in DC group. Methods: This was a cross-sectional study using prospectively collected data and samples obtained during routine diagnostic evaluation at referral hospitals. Thymidine kinase 1 was measured using chemiluminescence immunoassay and presented as median (and interquartile range). Nonparametric tests compared TK1F and TK1S between and within groups and Kendall's Tau assessed correlation between TK1F and TK1S. Results: Median TK1F was 7.48 (2.20-48.23) U/L in horses with lymphoma vs 2.50 (0.59-4.83) U/L in the DC group (P = .007); median TK1S was 4.26 (0.46-9.37) U/L vs 0.40 (0.40-0.75) U/L (P < .001), respectively. Both biomarkers showed good discrimination (area under the curve > 0.70) between lymphoma and the DC group, with optimal cutoff values of 5.7 and 2.5 U/L, respectively. Thymidine kinase 1 activity in body cavity fluid (3.62 [0.85-9.86] U/L) was significantly higher than TK1S (0.50 [0.40-2.09] U/L; P < .001) and there was no significant correlation between them within groups. Conclusions: Thymidine kinase 1 activity in body cavity fluid and TK1S provide different information and should be interpreted independently. They proved useful in lymphoma diagnosis, but not as a standalone test.

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Publication Date: 2026-09-27 PubMed ID: 42800046PubMed Central: PMC13615731DOI: 10.1093/jvimsj/aalag207Google Scholar: Lookup

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Summary
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MeSH
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Conflict of Interest
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Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

This study investigated the activity of thymidine kinase 1 (TK1) in serum and body cavity fluids of horses with lymphoma compared to diseased controls.
The goal was to determine if TK1 activities could serve as biomarkers to help diagnose lymphoma in horses and whether measurements in body cavity fluids provide additional diagnostic value over serum measurements.

Background

Thymidine kinase 1 (TK1) is an enzyme associated with cell proliferation and is often elevated in cancerous tissues.
Measuring TK1 in serum (TK1S) has shown variable accuracy as a lymphoma biomarker in horses, prompting research into other fluids such as body cavity fluids.
Body cavity fluids are fluid accumulations in spaces such as the chest or abdomen, potentially reflecting local tumor activity better than serum.

Objectives

Compare TK1 activity in body cavity fluids (TK1F) and serum (TK1S) between horses with lymphoma and diseased controls (horses with nonneoplastic gastrointestinal or respiratory diseases).
Determine if TK1F is higher than TK1S in horses with lymphoma.
Assess the correlation between TK1F and TK1S within and between groups.

Study Design and Methods

Cross-sectional study using prospectively collected clinical data and samples from referral hospitals.
20 horses diagnosed with lymphoma and 31 diseased control horses were included.
TK1 activity was measured using a chemiluminescence immunoassay, a sensitive technique for detecting enzyme activity.
Results were expressed as median values and interquartile ranges to describe central tendency and variability.
Statistical tests:
- Nonparametric tests to compare TK1F vs TK1S between groups (lymphoma and controls) and within groups.
- Kendall’s Tau to evaluate the correlation between TK1F and TK1S measurements.
- Receiver Operating Characteristic (ROC) curve and area under the curve (AUC) to assess the diagnostic accuracy of the biomarkers.

Key Findings

TK1 activity in body cavity fluid (TK1F) was significantly higher in horses with lymphoma (median 7.48 U/L) compared to diseased controls (median 2.50 U/L) with a P value of 0.007.
Serum TK1 activity (TK1S) was also significantly elevated in lymphoma cases (median 4.26 U/L) versus controls (median 0.40 U/L, P < 0.001).
Both TK1F and TK1S demonstrated good diagnostic discrimination between lymphoma and controls with area under the curve (AUC) values above 0.70:
- Optimal cutoff values were identified as 5.7 U/L for TK1F and 2.5 U/L for TK1S to differentiate lymphoma cases.
Within individuals, TK1 activity in body cavity fluid was significantly higher than in serum (median 3.62 vs. 0.50 U/L, P < 0.001).
No significant correlation was found between TK1F and TK1S within groups, indicating that these two measurements provide different biological or diagnostic information.

Conclusions

TK1 activity in both serum and body cavity fluids can be useful to support lymphoma diagnosis in horses.
Measuring TK1 in body cavity fluids offers additional diagnostic information that is not reflected by serum TK1 alone.
Because TK1F and TK1S are not correlated, they should be interpreted independently rather than interchangeably.
Although helpful, TK1 measurements are not definitive standalone diagnostic tests for lymphoma and should be combined with other clinical and laboratory findings.

Implications for Veterinary Medicine

Veterinarians may consider including TK1 activity in body cavity fluid analysis when lymphoma is suspected, especially if fluid samples are available from affected horses.
The combined assessment of TK1 in serum and fluids may enhance diagnostic accuracy but should be used as part of a comprehensive diagnostic workup.
Further research may be needed to refine cutoff values and validate these findings in larger cohorts and varied clinical settings.

Cite This Article

APA

Drozdzewska K, Burde S, Müller E, Merle R, Gehlen H. (2026). Thymidine kinase 1 activity in serum and body cavity fluids of horses with lymphoma. J Vet Intern Med, 40(5), aalag207. https://doi.org/10.1093/jvimsj/aalag207

Publication

Journal of veterinary internal medicine

ISSN: 1939-1676

NlmUniqueID: 8708660

Country: England

Language: English

Volume: 40

Issue: 5

PII: aalag207

Researcher Affiliations

Drozdzewska, Karolina

Equine Clinic, Freie Universität Berlin, Berlin, Germany.
Roseworthy Veterinary Hospital, School of Animal and Veterinary Sciences, Adelaide University, Roseworthy, Australia.

Burde, Sophie

Laboklin Laboratory for Clinical Diagnostics GmbH & Co. KG, Bad Kissingen, Germany.

Müller, Elisabeth

Laboklin Laboratory for Clinical Diagnostics GmbH & Co. KG, Bad Kissingen, Germany.

Merle, Roswitha

Institute of Veterinary Epidemiology and Biostatistics, Freie Universität Berlin, Berlin, Germany.

Gehlen, Heidrun

Equine Clinic, Freie Universität Berlin, Berlin, Germany.

MeSH Terms

Animals
Horses
Thymidine Kinase / blood
Thymidine Kinase / metabolism
Lymphoma / veterinary
Lymphoma / enzymology
Lymphoma / blood
Horse Diseases / enzymology
Horse Diseases / blood
Body Fluids / enzymology
Male
Female
Cross-Sectional Studies
Biomarkers, Tumor / blood

Grant Funding

Laboklin Laboratory for Clinical Diagnostics GmbH & Co. KG, Germany
Freie Universität Berlin

Conflict of Interest Statement

Sophie Burde and Elisabeth Müller are associated with Laboklin Laboratory for Clinical Diagnostics GmbH & Co. KG, which offers measurement of the thymidine kinase 1 activity described in the study. All authors declare that the interpretation of results and the preparation of the manuscript were conducted independently of the laboratory’s commercial interests. All other authors declare no conflicts of interest.

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