Ward et al developed the Symptom Index (SI) to help correlate clinical symptoms with evidence of acid reflux in patients undergoing esophageal pH monitoring. This can help establish a cause and effect relationship for what can be vague complaints.
Method:
(1) A patient undergoes 24 hour esophageal pH monitoring.
(2) Each time a symptom was experienced the patient records the time.
(3) Upon completion of the monitoring the symptom log is compared to the record of low esophageal pH readings (< 4). A symptom was considered to be associated with a low pH if the symptom occurs within 2 minutes of a reflux episode (4 minute window).
Symptoms to evaluate:
(1) heartburn
(2) chest pain
(3) any other symptom
symptom index =
= (number of times symptom noted when pH was < 4) / (total number of times symptom noted) * 100%
Interpretation:
• minimum SI: 0%
• maximum SI: 100%
• The higher the SI the greater the apparent linkage between acid reflux and symptoms
Symptom Index
Interpretation
< 25%
low SI
25 - 49%
50 - 74%
>= 75%
high SI
Limitations:
• Johnston et al (1994) stated that the index does not take into account the number of episodes with pH < 4 nor the total time period that the pH < 4. Interestingly the lead author found the SI useful for management of patients with GERD in 1992.
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