How EKHO and CRT works

The inner workings of the CRT test

EKHO & the Continuous Reaction Times (CRT) test

The CRT test has been the preferred method for diagnosis, grading and follow-up of covert/minimal Hepatic Encephalopathy for decades in the Danish Health System. A considerable body of research exists that support the method, and show that EKHO and the CRT test have proven useful for diagnosing and grading covert/minimal Hepatic Encephalopathy.

EKHO is a computerized implementation of the CRT test, that is very easy and reliable to use. It requires a minimum of time and no special skills of the clinician or the patient. It has also been shown, that CRT is unaffected by a number of confounding factors, such as age, gender, education and illiteracy. Furthermore there is no learning effect affecting the result of the tests.

The CRT test outputs a single number, the CRT-index that is a measure of the stability of the patient’s reaction and attention. The CRT method and the CRT index is a prime candidate for a psychometric test to routinely screen, grade and monitor covert/minimal Hepatic Encephalopathy in liver patients.

The test method

A CRT test is a series of measurements of the patient’s reaction time to an auditory stimulus. The patient is given 100-150 500Hz audio signals at roughly 90dB and must press a button in response to those stimuli. The stimuli come at random intervals between 2-5 seconds, and a complete test takes roughly 10 minutes to complete.

The result of the test is the CRT-index which is calculated on the basis of the percentiles of the reaction times (50 percentile / (90-10) percentile). This index is a good measure of the reaction and attention stability, and can be used to assess attention and cognition deficits.

A value of the CRT index of <1.9 discriminates between organic brain damage and Hepatic Encephalopathy with a sensitivity and specificity well above 90% and is used as a normal value treshold by the software.



The EKHO system implements the CRT method in a way, that makes it very easy to handle patients and conduct the tests. It uses custom-built hardware to measure the reaction times with an accuracy better than 1ms.

The EKHO software visualizes the reaction pattern of patients as both a scatter plot of the test series, as well as a distribution plot, enabling the test conductor to quickly assess the reaction pattern of the patient.

All the results, percentiles and the graphical representations are included in the printed report, that the system makes.


Stable reaction pattern of a healthy person

The patient reacts steadily without much variation throughout the entire test.

Unstable reaction pattern of a person with possible m/cHE

Large variations in the reaction times throughout the test.

Other Psychometric tests

EKHO and the CRT test compares very favorably with other psychometric tests, in that it requires very little skill and time to complete, and the result is independent of age, gender and a host of other factors.

The result is also very easy to interpret, and can be used to grade the severity of the patient’s condition.

International acclaim

The CRT test and the EKHO system has received very positive mention in the new international practice guideline for HE made in co-operation between the American and European Associations for the Study of Liver (AASLD & EASL).


 Further study

The information in this article is primarily based on an article called “The continuous reaction times method for diagnosing, grading, and monitoring minimal/covert hepatic encephalopathy.” by Mette Munk Lauridsen et al.

This and further articles can be found in the EKHO library.