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Clinical Research: Constipation Sections
Author Biography
Introduction
What is constipation?
Understanding the problem
Currently Selected Section: Objective Measurement
Subjective Measurement
Measuring Components
Precipitating Factors
Therapeutic Comparisons
Research Questions
Conclusion

Chapter 3: Methods for Clinical Research in Constipation: Objective Measurement of Constipation
          

Table 4.1 Rival Methods for Measure of Transit Time (MTT)
Click on each method for calculation details.

Method
Advantage
Disadvantage

Daily markers over several weeks:

All stools collected and markers counted (visually or by X-ray). MTT equal to turnover time

Most accurate MTTMost onerous for both patient and investigator

Different markers on 3 consecutive days:

MTT derived from count of markers in first stool passed on 4th day.

More accurate than single marker dose; less onerous than daily markers over several weeksMore onerous than single marker dose; less accurate than daily markers over several weeks

Single marker dose:

The weighted mean is calculated for the number of markers passed in each stool.

Least onerous for patient and investigatorLeast accurate

Figure 4.1 Radio-opaque markers
Graphic depiction of radio-opaque markers, described in text.
Radiograph of a stool containing three sizes of radio-opaque markers, collected as part of the estimation of intestinal transit time.

Problem 4.2

An example of the usefulness of different measurement methods is found in a study in which transit time was measured in a palliative care population using both MTT-S (single dose measure of transit time) and SST (single stool measure of transit time) techniques (Sykes, 1990).

In the study, MTT-S rather than MTT-C was used as the "gold standard" in order to minimize the impact on patients. The objective was to see if transit time could be accurately measured in this group, some of whom had marked degrees of gut slowing, by marker analysis of a single stool (SST).

Data from the study show that:

  • SST correlates very well with MTT-S, but the timing of the single stool giving this result varies according to the transit time in that population; and
  • SST works only in a homogeneous population, and the single stool, which will give an accurate measurement of transit time, will vary according to the transit time of the group.

  • If marker estimation of transit time is carried out in a mixed patient group, like the one in this study whose members vary widely in their transit times, or one in which the transit time is likely to be abnormal, MTT-C or MTT-S must be used.


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