# Effect of Hyperthermia on Prothrombin Time (PT), International Normalized Ratio (INR), and Activated Partial Thromboplastin Time (APTT)

## TL;DR

This study shows that higher temperatures, like those seen in fever, can significantly slow blood clotting times in lab tests.

## Contribution

The study demonstrates that hyperthermia prolongs PT, INR, and APTT in coagulation tests, which may affect clinical interpretations.

## Key findings

- PT increased significantly at 39°C, 41°C, and 43°C compared to 37°C.
- INR and APTT also showed significant increases with rising temperatures.
- Patients on anticoagulants or with liver disease had greater prolongation of clotting times.

## Abstract

Background

Coagulation testing in the laboratory is performed at 37°C. However, this in vitro testing may not reflect the in vivo pathophysiology affecting coagulation factors in clinical conditions that cause hyperthermia. This study aimed to evaluate the effect of hyperthermia on prothrombin time (PT), international normalized ratio (INR), and activated partial thromboplastin time (APTT).

Methodology

This cross-sectional analytical study was conducted in a teaching hospital in North India over a period of one and a half years. In total, 50 patients aged >18 years were randomly selected from the samples received for coagulation testing in the laboratory. PT and APTT were determined by the standard manual tilt tube method within four hours of collection. For PT, uniplastin 5 (ISI-1.1), and for APTT, Liquicelin-E (Tulip diagnostics) was used. PT and APTT were determined at three different hyperthermic temperatures (39°C, 41°C, and 43°C). Testing at the standard 37°C was also performed. Parametric data were reported as mean and standard deviation, while non-parametric data were reported as median and interquartile range. The variation in PT/INR and APTT results at four designated temperatures was analyzed by repeated-measures analysis of variance. Statistical analysis was performed using SPSS version 16.0 (SPSS Inc., Chicago, IL, USA).

Results

Mean PT at 39°C, 41°C, and 43°C was 16.0 ± 7.1 seconds, 17.2 ± 9.6 seconds, and 19.7 ± 14.4 seconds, respectively. Mean PT at 37°C was 15.1 ± 4.9 seconds. The difference was statistically significant (p = 0.001). Mean INR at 37°C, 39°C, 41°C, and 43°C was 1.2 ± 0.4, 1.3 ± 0.6, 1.4 ± 0.9, and 1.6 ±1.4, respectively. The rising trend with increasing temperatures was significant (p = 0.004). Mean APTT at 37°C, 39°C, 41°C, and 43°C was 30.3 ± 11.6 seconds, 32.6 ± 11.5 seconds, 36.2 ± 13.2 seconds, and 42.5 ± 14.7 seconds, respectively. The difference was statistically significant (p < 0.001).

Conclusions

This study showed significant prolongation of PT, INR, and APTT at hyperthermic temperatures. The degree of prolongation of clotting times was greater in patients on oral anticoagulant therapy and those with liver disease.