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PhaosawasdiK, etal. BMJ Open Gastro 2022;9:e000976. doi:10.1136/bmjgast-2022-000976
Prevalence of achlorhydria in an Asian
population detected using Congo red
staining during routine gastroscopy: 22
years’ experience from a single centre
Kamthorn Phaosawasdi,1 Yingluk Sritunyarat,2 Chawin Lopimpisuth ,2
Nutbordee Nalinthassanai,2 Yongkasem Vorasettakarnkij,3
Pradermchai Kongkam2,3
To cite: PhaosawasdiK,
SritunyaratY, LopimpisuthC,
etal. Prevalence of achlorhydria
in an Asian population detected
using Congo red staining
during routine gastroscopy:
22 years’ experience from a
single centre. BMJ Open Gastro
2022;9:e000976. doi:10.1136/
bmjgast-2022-000976
►Additional supplemental
material is published online
only. To view, please visit the
journal online (http:// dx. doi.
org/ 10. 1136/ bmjgast- 2022-
000976).
Received 11 June 2022
Accepted 10 August 2022
1Gastrointestinal and Liver
Clinic and Endoscopy Unit,
Vichaiyut Hospital, Bangkok,
Thailand
2Excellence Center for
Gastrointestinal Endoscopy,
King Chulalongkorn Memorial
Hospital, Bangkok, Thailand
3Department of Medicine,
Division of Hospital and
Ambulatory Medicine,
Chulalongkorn University
Faculty of Medicine, Bangkok,
Thailand
Correspondence to
Dr Pradermchai Kongkam;
kongkam@ hotmail. com
Endoscopy
© Author(s) (or their
employer(s)) 2022. Re- use
permitted under CC BY- NC. No
commercial re- use. See rights
and permissions. Published
by BMJ.
ABSTRACT
Objective We aimed to study the prevalence of
achlorhydria (AC) in a large Asian population.
Design Medical records of patients who underwent
oesophagogastroduodenoscopy (OGD) with Congo red
staining method at the Vichaiyut Hospital from January
2010 to December 2019 were retrospectively reviewed.
Results A total of 3597 patients was recruited; 223 were
excluded due to concurrent use of proton pump inhibitors.
Eighteen from 3374 patients (0.53%) had AC. Seven
patients were presented with permanent AC (5F, 2M)
(median age=69 years; range 58–92). Among 11 patients
with temporary AC (5M, 6F: mean age 73.4 years; SD 13.2
years), all had gastrointestinal Helicobacter pylori bacterial
infection and were over 45 years old. After successful
treatment for H. pylori, AC was absent among patients
with temporary AC. If counting only patients over 45 years
of age, the prevalence of AC was 0.68% (18/2614). No
adverse events arising from Congo red occurred.
Conclusion AC is relatively rare. Permanent and
temporary AC were found only when they were over 55
and 45 years old, respectively. Staining Congo red on
gastric mucosa can be safely and routinely incorporated
into the OGD procedure for early detection of AC. We
recommended a low- cost screening test such as serum
vitamin B levels for screening only in patients aged 50 and
over.
INTRODUCTION
Achlorhydria (AC) refers to a state in
which the stomach is unable to produce
hydrochloric acid, which is a significant
component of gastric secretions produced
by the stomach. The acid digests food and
protects the body from foodborne patho-
gens. Gastric acid are fluids secreted by the
stomach, consisting of hydrochloric acid,
potassium chloride and sodium chloride.
Parietal cells lining the stomach wall are
the cells responsible for producing gastric
acid. Various factors can damage these cells
include surgery, bacteria (Helicobacter pylori),
WHAT IS ALREADY KNOWN ON THIS TOPIC
⇒Achlorhydria (AC) is relatively rare.
⇒Prevalence of AC has been reported in only small
and selective samples of patients.
⇒Early detection of AC can prevent irreversible brain
damage from pernicious anaemia which can lead to
irreversible neurological decit.
⇒Gastroscopy has been increasingly used worldwide.
⇒Congo red testing during gastroscopy can be simply
used to identify AC on- site.
WHAT THIS STUDY ADDS
⇒In our study, AC is only present in patients over 45
years of age.
⇒Our prevalence of AC from a large Asian population
is demonstrated to be rarer than previously reported
from Western country.
⇒Systematic use of Congo red testing during oesoph-
agogastroduodenoscopy can be done with little to
no extra burden or adverse events as shown by two-
decade procedural implementation.
⇒All patients with permanent AC in our study were
aged 55 years or older at the time of diagnosis.
⇒Given the low prevalence of the AC, although it can
cause a serious complication, we recommend a
low- cost screening test such as serum vitamin B12
levels for screening only in patients aged 50 and
over.
HOW THIS STUDY MIGHT AFFECT RESEARCH,
PRACTICE, OR POLICY
⇒This present study shows that AC is rare, seen only
in patients over 50 years of age. Screening is quick
and easy with the Congo red test during an upper
gastrointestinal endoscopy. The information from
this current study is therefore one of the important
pieces of information to be taken into consideration
regarding screening policy for the disease: should
doctors consider screening methods for this disease
in the future? To our knowledge, no study of the dis-
ease in such a large number of Asian ethnicities has
been reported before.
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Open access
medication and certain antibodies which may lead to AC
among patients.
AC can be categorised into two groups based on its
causes: (1) permanent achlorhydria (permanent AC),
whose condition is irreversible; and (2) temporary achlo-
rhydria (temporary AC), whose cause or association with
certain diseases can be cured. One example being infec-
tion with H. pylori in the stomach and using a proton
pump inhibitor.
AC can lead to several diseases or conditions. One
condition is pernicious anaemia (PA) where the process
of vitamin B12 absorption has been altered. The pres-
ence of PA leads to irreversible neurological deficits,
which includes the following neurological symptoms:
personality changes, cognitive impairment, paresthesia,
psychosis, dementia, weakness of muscle, paraplegia and
urinary incontinence. Detecting AC is crucial since reme-
dies are often available.
Diagnostic techniques for AC can be performed in a
number of ways. One simple method is to diagnose while
the physician is performing an oesophagogastroduode-
noscopy (OGD). This method involves staining Congo
red on the gastric mucosa. Congo red is pH sensitive
and changes its colour from red to dark blue or black
in an acidic environment which is the body’s normal
condition. When patients have AC, Congo red does not
change colour. Staining the gastric mucosa only takes a
few additional minutes during OGD. Congo red can be
completely washed off with normal rinse. The use of dye
in the digestive tract is not harmful to the body.
In this current study, researchers collected data from
a large referral hospital in Thailand which has incorpo-
rated Congo red staining of gastric mucosa as protocol
during OGD since 1998. The procedure was performed
in all patients who had undergone OGD with no contra-
indications for the use of Congo red for staining of gastric
mucosa. The primary objective is to determine the prev-
alence of AC among this population with a secondary
objective to identify the clinical features of patients with
AC. Ascertainment of the likely cause of AC in each
patient will also be investigated.
METHODS
Medical records inspection
This study conducted a large single- centre retrospective
examination of medical records of patients that under-
went OGD at Vichaiyut Hospital in Bangkok, Thailand
from January 1998 to December 2019. Inclusion criteria
were patients undergoing successful OGD by means of
various indications and staining of gastric mucosa with
Congo red. Exclusion criteria were patients taking either
a proton pump inhibitor or histamine receptor antago-
nist within 2 weeks before the procedure. For patients
with positive Congo red results, researchers conducted
a comprehensive review of patient data including the
results of the OGD, results of gastric mucosa staining and
clinical background information. The data were then
summarised and analysed. The protocol was approved by
the Ethics Committee of the Vichaiyut Hospital.
Procedure for detection of AC using Congo red
While performing the routine OGD, the following
sequence of steps are taken. The physician inserts a gastro-
scope into the patient’s upper digestive area to check the
mucosa of the stomach and duodenum to determine if
there are cancerous or non- cancerous lesions. A small
tube is then inserted through the instrument channel
of the gastroscope to protrude into the stomach area.
A 10 cc syringe containing Congo red paint is sprayed
through the rubber tube on the gastric mucosa in the
body of the stomach. Through visual identification, any
colour change of the gastric mucosa is identified. The
diagnostic criterion for AC is no change in the colour of
Congo red (figure 1). If Congo red is exposed to acidic
conditions, the colour will change from red (pH 5.0)
to dark blue or black (pH 3.0) (figure 2; online supple-
mental videos 1 and 2, respectively).
Figure 1 Congo red does not change its colour because
there is no acid on gastric mucosa.
Figure 2 Congo red changes its colour from red to dark
blue or black in an acidic environment.
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Monitoring and isolating patients with AC
According to protocols at Vichaiyut Hospital, patients
confirmed with AC were advised that determination of
the cause according to clinical information from history
taking, physical examination and further inspection
would be undertaken. Physicians would also recommend
for patients to attend regular follow- up appointments to
treat AC and its underlying causes. Further inspection
recommended by the physician included pathological
examination of the gastric mucosa, gastrin level, H. pylori
infection and vitamin B12 blood test.
Results obtained from the examination and extracted
from the patient records were studied by the researchers.
The patients were divided into two groups: the first
group included patients with permanent AC. Due to
the unknown aetiology of permanent AC, this group of
patients was treated with vitamin B12 to prevent compli-
cations such as neurological deficits and anaemia. The
second group included patients with temporary AC who
were treated and received follow- up examinations to
determine if AC and the diseases which caused it had
improved. If the physician was unable to treat the cause
of the disease or the treatment took a long time, the
physician would also treat AC with B12 supplements to
prevent complications from such a condition.
Statistical analysis
The researchers presented demographic and clinical
characteristics of individuals found with AC using counts
and percentages. Prevalence calculations are presented
as a number and percentage. No statistical tests were
performed.
RESULTS OF STUDY
A review of medical records at Vichaiyut Hospital from
January 1998 to December 2019 revealed that a total of
3597 patients had undergone OGD and the Congo red
method. All patients met the inclusion criteria; 223 were
excluded due to concurrent use of proton pump inhib-
itors or histamine receptor antagonists within 2 weeks
before the procedure. Eventually, 3374 were recruited in
the study. A total of 18 patients were found to have had
AC, 7 of whom were categorised as permanent AC and
11 as temporary AC. The total prevalence of AC among
subjects was 0.53% (18/3374) (figure 3)
Clinical data on the seven patients with permanent AC
are shown in table 1.
Five of the seven patients (71.4%) with permanent AC
were women and two (38.6%) were men. The mean age
of patients at diagnosis time was 74.6 years (SD 11.9). The
second patient who tested positive for H. pylori infection
was categorised as having permanent AC since AC could
still be detected after successful treatment for H. pylori.
All patients were found to have high levels of serum
gastrin (median=3000 pg/mL; range=1300–3000 pg/
mL). All patients in this group were confirmed with
intestinal metaplasia from pathological results from the
gastric mucosa (table 2).
Clinical data on the 11 patients with temporary AC are
shown in table 3.
Five were men (45%) and six were women (55%).
Patients had a mean age of 73.4 years (SD 13.2 years). All
patients in this group had gastrointestinal H. pylori bacte-
rial infection while being examined with Congo red.
After treatment for H. pylori, patients were re- examined
with Congo red and AC was absent.
After completing an OGD at Vichaiyut Hospital, a
follow- up typically would occur 1 day after a procedure
was performed. The patient would either meet the physi-
cian or would be contacted via telephone by the nursing
team or medical personnel to monitor their condition.
Review of all data found that no patients had complica-
tions arising from the Congo red procedure in this study.
DISCUSSION
The present study included a large number of subjects
from a single institution over a period of 10 years. To our
knowledge, this present study has the largest number
of participants. Past studies have a smaller population.
Demographics tend to be niche populations that are
more likely to be AC than the general population. It is
therefore not surprising that the prevalence of AC in
this current study was lower than that reported in other
previous studies such as a prospective survey by Carmel et
al that was conducted to determine cobalamin levels and
anti- intrinsic factor antibodies in 729 people who were
over 60 years of age. It was found that 14 of them were
present with PA, which accounts for 1.9%. Most of the
patients were asymptomatic with no anaemia.1 Bins et al
studied a blood test for serum gastrin levels after patients
had been fully stimulated with pentagastrin. In the diag-
nosis of AC in the Bins et al study, the prevalence of AC
was found to be 2.5%.2 A prospective survey by Carmel
et al was conducted to determine cobalamin levels and
Figure 3 Diagram showing ow and number of patients
involved in this current study. AC, achlorhydria; OGD,
oesophagogastroduodenoscopy; PPI, proton pump inhibitor.
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Open access
anti- intrinsic factor antibodies in 729 people who were
over 60 years of age. It was found that 14 of them were
present with PA, which accounts for 1.9%. Most of the
patients were asymptomatic with no anaemia.3 In the
Jacobson et al study, the type of population was patients
with autoimmune disease.4 The prevalence of AC from
other studies has been estimated at 2%, while the preva-
lence of permanent AC in this study was 0.19%, a rate 10
times smaller. The reason for such a difference is that the
types of studies and population were different, especially
in terms of the groups or characteristics of the popula-
tion who participated in the study.
Ethnicity is likely another factor since Asians have been
found to have a lower prevalence of AC than other races
according to past studies and our study was exclusively
an Asian population. Data indicate that the prevalence of
the disease varies between races. In a study of 156 patients
in Europe, 73 patients were European in origin, mean
age among black women (53±1) was lower than that of all
the others, and another study found that Latin- American
people with pernicious anaemia were both significantly
younger than white men and women.1 5
One interesting information from the results of this
study is that permanent AC is found only in the popu-
lation aged 55 years and over, but including temporary
AC, it is found only in the population aged 45 and over.
This is an important issue because if we look at PA as
a disease that causes disability and may be the cause of
death, and if we can diagnose in the first place before
the patient has consequences of neurological diseases,
treatment would be very easy with the cheap cost of treat-
ment. Therefore, we should have a plan for screening
for AC at an appropriate age of patients. However, there
may be some objections that, given the low prevalence of
the disease, screening tests are not appropriate. Never-
theless, if we look closely, we will find that screening for
AC is very simple and cheap if not counting the endo-
scopic examination, which is the method used in this
present research. Another interesting method is to test
vitamin B12 levels, which is easy, inexpensive and patients
do not need an endoscopy. Considering this study’s data
which found that this disease is found only in patients
aged 45 years and over, we may therefore have future
studies to study whether it is worthwhile or not that we
will only screen for AC in patients aged 50 years and over
by using a cheap and easy way to do it in general such
as checking vitamin B12 levels, but at the same time, if
the patient is required to undergo a gastroscopy, we may
consider using Congo red test used in this current study.
Nevertheless, the data presented in this current study, in
fact, do not support that Congo red screening is appro-
priate as the very low detection rate suggests that it is
not worthwhile. It seems to be more reasonable for us to
suggest that vitamin B12 screening may be an appropriate
routine test in those with risk factors with age more than
50 years.
Table 1 Characteristics of patients with permanent AC
Patient number Age (years)
Serum vitamin B12 (pg/mL)
(normal value=187–883 pg/mL) Anti- intrinsic factor Serum gastrin level (pg/mL)
1 58 2000 Positive 2000
2 86 2000 Positive 3000
3 69 405 Positive 3000
4 69 224 Negative 1300
5 80 1642 Positive 3000
6 92 265 Positive 3000
7 68 100 Negative 2100
AC, achlorhydria.
Table 2 Light microscopic nding among patients with permanent AC
Patient number Finding Pathology nding
1 Focal area of mild gastritis at body, fundus and antrum Mild chronic gastritis with IM mature type
2 Focal area of mild gastritis at antrum Mild chronic gastritis with IM mature type
3 Atrophic gastritis at body and fundus, mild gastritis at antrum Mild chronic gastritis with IM mature type
4 Focal area of mild hyperemia at antrum Mild chronic gastritis with IM mature type
5 Focal area of mild gastritis at antrum Mild chronic gastritis with IM mature type
6 Focal area of mild gastritis at antrum Mild chronic gastritis with IM mature type
7 Focal area of mild gastritis at antrum Mild chronic gastritis with IM mature type
AC, achlorhydria; IM, intestinal metaplasia.
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Open access
This present study showed the use of the Congo red
method during OGD, which is a very convenient way of
diagnosing AC from gastric mucosa. The process can be
carried out with ease and safety, taking only an additional
few minutes during an OGD. The results are also immedi-
ately produced and reportable. Using Congo red is a safe
method because it causes no adverse event. In terms of
the efficacy of AC detection, a prospective study by Tóth
et al assessed the efficacy of the Congo red technique in
106 patients with the maximal acid output of less than
6.9 mmol/hour in men and 5.0 mmol/hour in women.
The accuracy of the Congo red method was as high as
0.98 (95% CI 0.93 to 0.99).6 Moreover, using endoscopic
findings from OGD alone is not sensitive enough to detect
early stages of gastritis that have AC conditions such as
early staged autoimmune gastritis. The use of Congo red
in combination with OGD can help endoscopists better
diagnose AC and be more sensitive.7 8
Other methods that can be used to diagnose AC
were reported as follows. Measuring vitamin B12 level is
another method which can detect patients with vitamin
B12 deficiency. It is not the most efficient way because
the threshold for vitamin B12 deficiency is a value of
less than 100 pg/mL, while simply being below average
is less than 200 pg/mL.9 10 Examination of parietal cell
antibodies and intrinsic factor antibodies is also useful in
detecting patients with AC and PA, with intrinsic factor
antibodies being more specific but less sensitive than
anti- parietal cell antibodies. The sensitivity and specificity
of anti- parietal cell antibodies were found to be at 81%
and 90%, respectively, while sensitivity and specificity
of anti- intrinsic factor antibodies were 27% and 100%,
respectively.11
In conclusion, results from this study which used the
Congo red technique to detect AC during gastroscopy
indicated that such a method could be easily used to diag-
nose AC. Nevertheless, given that the prevalence of AC
in this current study was low, using vitamin B12 level in
the high- risk group as a screening test seems to be more
reasonable than the Congo red test. While the preva-
lence of AC in this current study was much less than that
of AC reported in other studies, the characteristics of the
population were different both in terms of ethnicity and
types of population that were examined. The methods
of testing were also different. Future prospective studies
should be conducted to explore the benefits of using
simple methods such as vitamin B12 level to detect AC in
the population over 50 years old.
Contributors KP: guarantor, data curation, formal analysis, writing—original draft,
writing—review and editing. YS: data curation, writing—review and editing. CL:
writing—review and editing. NN: data curation, writing—review and editing. YV:
writing—review and editing. PK: data curation, formal analysis, writing—original
draft, writing—review and editing.
Funding The authors have not declared a specic grant for this research from any
funding agency in the public, commercial or not- for- prot sectors.
Competing interests None declared.
Patient consent for publication Not applicable.
Ethics approval Not applicable.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available on reasonable request.
Open access This is an open access article distributed in accordance with the
Creative Commons Attribution Non Commercial (CC BY- NC 4.0) license, which
permits others to distribute, remix, adapt, build upon this work non- commercially,
and license their derivative works on different terms, provided the original work is
properly cited, appropriate credit is given, any changes made indicated, and the
use is non- commercial. See:http://creativecommons.org/licenses/by-nc/4.0/.
ORCID iD
ChawinLopimpisuth http://orcid.org/0000-0003-0308-4986
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Patient number Age Sex
Serum gastrin
(pg/mL) HP status Pathology nding
1 82 M 84 Positive IM chronic gastritis
2 80 F N/A Positive IM mature type with atrophic gastritis
3 65 M N/A Positive Mild chronic gastritis
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9 62 F 200 Positive HP- related gastritis
10 64 M 96 Positive HP- related gastritis
11 101 F 250 Positive Mild chronic gastritis with IM mature type
AC, achlorhydria; HP, Helicobacter pylori; IM, intestinal metaplasia; N/A, not available.
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