|
|
Utility of Spot Testing Kit in the Assessment of
Iodine Content of Salt- A Multicentric
Study
Department
of Human Nutrition
All India
Institute of Medical Sciences
New
Delhi-110029
1999
Principal
Investigators
1. Dr. Subhadra Seshadri,
Head,
Department of Foods & Nutrition,
M S University,
2. Dr. S. S. Swami,
Head,
Department of Prevalence and Social Medicine,
3. Ms. Beena,
Chief Co-ordinator,
Mamta Samajik Sanstha,
53-c,
Deharadun.
4. Dr. B.P. Mathur,
Reader,
Department of Preventive and Social Medicine,
5. Dr. T.D. Sharma,
Principal,
Health and Family Welfare and Social Medicine,
Kangra,
District Kangra (H.P.)
6. Dr. Kumud Khanna,
Director,
7. Dr. Rita Singh Raghuvanshi,
Reader & Senior Research Officer,
Deptt. of Foods & Nutrition,
GBPUAT, Pantnagar,
District Udham Singh Nagar (U.P.)
8. Dr. Umesh Kapil,
Additional Professor,
Department of Human Nutrition and Gastroenterology,
All India Institute of Medical Sciences,
New Delhi-110029.
And
Dr. S.N. Dwivedi,
Associate Professor and Head,
Department of Biostatics,
All India Institute of Medical Sciences,
New Delhi-10029
(Central Co-ordinating Unit)
Editors
Dr. Umesh Kapil
Additional Professor,
Human Nutrition Unit,
All India Institute of
Medical Sciences,
Ansari Nagar, New
Delhi-110029.
Dr. S.N. Dwivedi
Associate Professor and
Head
Department of Biostatics,
All India Institute of
Medical Sciences,
Ansari Nagar,
Assistant Editors
Monica Tandon*
Priyali Pathak*
Ritu Pradhan*
* Research Scientists,
Department of Human
Nutrition,
All India Institute of
Medical Sciences,
New Delhi-110029
List of Contents
Contents
1. Executive Summary
2. Introduction
3. Objective
4. Research Methodology
5. Results
6. Discussion
7. References
8. Appendices
List of Tables
Tables
Table 1 Total Number of Salt Samples Analysed
Table 2 Iodine Content of Salt Samples by
Iodometric Titration Method
Table 3 Iodine Content of Salt Samples at
Different centres
By Both STK and IT Method
Table 4 Analysis of Salt Samples at Different
Centres
by both STK and IT Method
Table 5 Specificity
and Sensitivity of STK Against IT Method at Different Centres Studied
Table 5.1
Table 5.2
Table 5.3 Dehradun
Table 5.4
Table 5.5 Kangra
Table 5.6
Table 5.7 Udham
Singh Nagar
Table 5.8
Table 6 Pooled
Analysis of Results of Eight Centers
Table 7 Sensitivity,
Specificity, PPV and NPV of STK
against
Iodometric Titration Method at
different
Centres
List of Appendices
I. List
of Different Centres Participating in the Multicentric
Study
for Assessment of Utility of Spot Testing kit
II. Research
Methodology for Collection of Salt Samples
III. Estimation
of Iodine Content in salt by Iodometric Titration
IV. Use
of Spot Testing Kit
V. Brief
Note on Sensitivity and Specificity
VI. Internal
Quality Control Procedure Adopted in IT Method
VII. Evaluation
of Universal Salt Iodisation in
(Excerpts
from the detailed report)
Abbreviations Used
AIIMS : All
India Institute of Medical Sciences
IDD : Iodine Deficiency Disorders
IHE :
IT :
Iodometric Titration
LDPE : Low
Density Poly Ethylene
PPM : Parts Per Million
RTM : Research Team Members
STK : Spot Testig Kit
UNICEF : United
Nations Children’s Fund
WHO : World Health Organization
Acknowledgements
We would like to thank Dr. Sheila Vir, Project Officer,
1. Executive
Summary
The
use of iodised salt has been evolved as a major strategy to combat Iodine
Deficiency Disorders (IDD). IDD are preventable by supplementing the diet
regularly with iodine. Iodine concentration to be added in the salt is
specified as the number of parts of iodine per million parts of salt, or “ppm”.
Salt should contain at least 15 ppm iodine to provide the normal requirements
of 150 micrograms per day to the consumer. Careful monitoring and control of
iodine levels at the production, storage, sale and consumption stages, and
prevention of use of uniodated or substandard iodised salt, are vital
components of universal salt iodisation programme. For the successful
implementation of this strategy, monitoring the quality of iodised salt is
essential. The iodine content of iodised salt is estimated routinely by the standard “Iodometric Titration” (IT)
method in the laboratory. However, a simple Spot Testing Kit (STK) containing
starch solution has been advocated as a method for semi-quantitative estimation
of iodine content in salt.
The
present multicentric study was conducted with the objective to assess the
utility of the STK (against the standard
iodometric titration) in the semi-quantitative estimation of iodine in salt.
The
study was conducted at eight centres in the country, namely, Baroda, Bikaner,
Dehradun, Jhansi, Kangra, New Delhi (IHE), Udham Singh Nagar and New Delhi
(AIIMS) co-ordinated by the Department of Human Nutrition, All India Institute
of Medical Sciences, New Delhi. Uniform protocol was utilised at all the eight
centres to conduct the study.
The
iodine content of more than 700 salt samples at each center (total 6302 salt
samples) was estimated by two different methods i.e. IT and STK method
and the results were compared. The
results of IT method were used as reference standard for comparison. The
Sensitivity, Specificity, Positive Predictive Value (PPV) and Negative
Predictive Value (NPV) of the STK method in relation to the IT was calculated,
using the standard formulae.
The
sensitivity of the STK method reported at different centers ranged from 80.7%
to 95.59%, with an average sensitivity
of 89.8% (as calculated after pooling the data of eight centers). The
specificity reported from various research centres also ranged from 50.5% to
100.0% with an average specificity of 65.6%.
The
present study revealed that for semi quantitative estimation of iodine in
salt, STK method has a high sensitivity
but relatively low specificity. These findings suggest that STK method can be
used for semi-quantitative estimation of iodine by the government and
non-government functionaries for assessment of iodine content of salt for the
purpose of monitoring the quality of salt available to the community.
It
is further recommended that for monitoring the quality of iodised salt
available to the community members, it is necessary to analyze a large number
of salt samples to visualize the trend. In this context, the STK can prove a
simple and useful tool as compared to IT which requires laboratory facilities.
2. Introduction
The
use of iodised salt has been evolved as a major strategy to combat Iodine
Deficiency Disorders (IDD). IDD are preventable by supplementing the diet
regularly with iodine. An inexpensive and effective preventive method is to add
iodine to salt. Iodine concentration is specified as the number of parts of
iodine per million parts of salt, or “ppm”. Salt should contain at least 15 ppm
iodine to provide the normal requirements of 150 micrograms per day to the
consumer. It is usually necessary to iodate the salt at higher levels (50 ppm
or more) to compensate for the loss of iodine in storage and distribution.
There are many studies to show that when salt without iodine was provided to
population, it has no impact on IDD. On the other hand IDD has been eradicated
in many countries by ensuring an effective level of iodine in the salt. Careful
monitoring and control of iodine levels at the production, storage, sale and
consumption stages, and prevention of use of uniodated or substandard iodised
salt, are vital components of universal salt iodisation programme. For the
successful implementation of this strategy, monitoring the quality of iodised
salt is essential. The iodine content of iodised salt is estimated routinely
by the standard “Iodometric Titration”
(IT) method in the laboratory (1). However, recently a simple kit has been
developed by MBI chemicals Ltd.,
3. Objective
The
present study was conducted with the objective to assess the utility of the
STK (against the standard iodometric
titration) in the semi-quantitative estimation of iodine in salt.
4. Research
Methodology
The
present multicentric research project was conducted at eight centres in the
country, namely, Baroda, Bikaner, Dehradun, Jhansi, Kangra, New Delhi (IHE), Udham
Singh Nagar and New Delhi (AIIMS). The research project was co-ordinated by the
Department of Human Nutrition, All India Institute of Medical Sciences,
The
iodine content of each salt sample was estimated by two different methods i.e.
IT and STK method and the results were compared. The results of IT method was used as
reference standard for comparison.
More
than 700 salt samples were collected at each of the 8 centres selected for the
study (Appendix II). Each salt sample was given an identification number and
was analysed for its iodine content by IT method (Appendix III) by a research
scientist. Subsequently, the salt samples were
recoded and tested again for the iodine content by the STK method (As
the scientist was given recoded samples, he was not aware about the results of
IT method).
The
procedure for use of STK was as follows: The STK consists of a test solution
(A), and a recheck solution (B). One
drop of test solution (A) was added to about 5 gm of salt sample. The change in
colour of the salt sample ranged from white (no change in colour) to dark
violet depending on the iodine content of salt, i.e. Nil, less than 15
ppm, and 15 ppm and above, which was compared with the standard colour chart
provided with the STK. If on addition of test solution (A), no change in colour
of salt was observed, the recheck solution (B) was added. This was done to make
the salt medium acidic, in case the salt had alkaline constituents,
subsequently, the test solution (A) was added again. The intensity of the blue
colour was directly proportional to the iodine content of salt (Appendix IV).
For
the purpose of present study, the results of iodine content of salt as analysed
by STK method was reported under two categories i) salt samples with less than
15 ppm of iodine and ii) salt samples with 15 ppm and more of iodine.
The
Sensitivity, Specificity, Positive Predictive Value (PPV) and Negative
Predictive Value (NPV) of the STK method in relation to the IT was calculated,
using the standard formulae (Appendix V) (4).
The
sensitivity of STK was calculated as the percentage of salt samples truly
identified by STK as having 15 ppm and more of iodine content (usually known as
positives) of those positives identified by the IT method also. Sensitivity was
calculated as the ability of a test (STK) to identify correctly all those salt
samples which had more than 15 ppm iodine content; that is, true positive. A 90
per cent sensitivity of STK means that 90 per cent of the salt samples screened
by the STK test will give a “true positive” result and the remaining 10 per cent
as “false negative” result where negative means samples having less than 15 ppm
of iodine content.
Similarly,
the specificity was calculated as the percentage of salt samples truly
identified by the STK as having less than 15ppm of iodine content (usually
known as negatives) of those negatives
identified by IT method. Specificity was calculated as the ability of a test
(STK) to identify those salt samples which do not have salt iodine content more than 15 ppm, that is, “true negative”. A
90 per cent specificity of STK means
that 90 per cent of the salt samples having iodine content less than 15 ppm
will give “true negative” results by the STK test and remaining 10 per cent of
the salt samples who have iodine content less than 15 ppm, screened by the STK
test will be wrongly classified as having more than 15 ppm iodine content.
The
PPV was determined as the percentage of salt samples with iodine content of 15
ppm or more indicated by IT out of those
identified by the STK. On the other hand, the NPV was determined as the
percentage of salt samples with less than 15ppm iodine content indicated by the
IT method out of those identified by the STK (2).
Each
centre conducted the internal quality control program with each batch of salt
samples analysed by them (Appendix VI).
Under
National Iodine Deficiency Disorder Control Programme (NIDDCP) it is stipulated
that, at the beneficiary level, the salt should contain a minimum of 15 ppm of iodine.
In the present study, ability of STK method was compared to correctly identify
the salt samples with 15 ppm and more when compared with the standard IT
method.
4.1 Calculation of
Sample Size
With an anticipated
agreement between iodometric titration method and spot testing kit as 85%
(5) and assuming ideal agreement as 80%,
to have level of confidence of 95% as well as power of the study 95%, the
minimum sample size required was calculated to be approximately 660. To have higher precision, it was decided to
undertake study with sample size of 700 at each centre.
4.2 Interpretation of sensitivity and specificity
A
sensitive test will correctly identify a high proportion of samples of salt
that have a stipulated concentration of iodine. A specific test will rarely
give a positive result in a sample of salt which actually has less than the
specified minimum concentration of iodine. In all spot test, there is a trade
off between sensitivity and specificity, the ideal spot test would be one which
has both i.e. high sensitivity and high specificity.
4.3 Nature of the Spot Testing Kit in Use
All
known salt test kits in use are based on the long known ‘iodine/starch’
reaction. The kit which is designed to test for iodate, contains potassium iodide,
soluble starch, sulfuric acid and stabilizers. The iodide reacts with iodate,
in the presence of acid, to liberate free iodine. The iodine reacts with starch
to give a strong blue colour known as the starch-iodine complex.
When
the kit reagent is dripped onto dry salt, a blue colour develops, the intensity
of which is approximately proportionate to the concentration of iodate in the
salt-over a certain range. The intensity of the colour also depends on other factors which include
temperature, colour of the salt, particle size of the salt, moisture content of
the salt, and type of starch used in the
preparation of the test kit.
5. Results
A
total of 6302 salt samples were collected and analysed at eight different centers
in the country out of which 18.8% samples were of crystalline variety (Table
1). Analysis of salt samples by
iodometric titration revealed that 38% samples had less than 15 ppm and 62% had
15 ppm and more of iodine content (Table 2). By STK method 31.3% salt samples
had less than 15 ppm of iodine and 68.7% had iodine content of 15 ppm and more
(Table 3). Table 4 reveals the results of salt iodine content by STK and IT
method.
The
sensitivity of spot testing kit was assessed in terms of the number of salt
samples having 15 ppm and more iodine correctly identified by STK method
against the total number of salt samples identified as having 15 ppm and more
iodine by titration method.
The
results of sensitivity and specificity of STK against iodometric titration
method assessed at eight different centres in the country has been depicted in
tables 5.1 to 5.8. The highest sensitivity of STK was reported by Pant Nagar
(Udham Singh Nagar) centre (95.5%). The sensitivity of various research centers
ranged from 80.7% to 95.5% (Table 7).
The
specificity was determined as the number of salt samples having <15 ppm
iodine correctly identified by STK method against the total number of salt
samples identified as having <15 ppm iodine by titration method. The
specificity of various research centres ranged from 50.4% to 100.0% (Table 7).
The
PPV was determined as the percentage of salt samples with iodine content 15 ppm
or more as indicated by STK method and titration methods both to the total
number of samples with iodine content 15 ppm or more as indicated by the STK
method. The positive predictive value of the various research centres ranged
from 58.4% to 100.0% (Table 7).
Conversely,
the NPV was expressed as the percentage of salt samples with iodine content
<15 ppm as indicated by STK method and IT method both to the total number of
samples with iodine content <15 ppm as indicated by the STK method. The NPV
of the various research centres ranged from 26.8% to 90.4% (Table 7).
6. Discussion
Iodometric
titration is the recommended method for assessment of iodine content of salt.
However, it requires a laboratory set up and trained manpower. The STK method
is simple and can be used by peripheral health functionaries, school teachers,
community leaders and traders without any formal training. The STK method is
recommended by the Government of India for qualitative assessment of iodine in
salt to be used routinely by the government and non-government functionaries.
The present study revealed that STK method had an average sensitivity of 89.8%
and specificity of 65.6%.
A
study conducted by Indian Institute of Health Management Research, Jaipur in
1997 on salt samples collected from seven different states also reported the
sensitivity of STK between 77% to 99.2% and specificity from 23.7 to 77.2% in different states (2) (Appendix VII).
The
present study revealed that for semi-quantitative estimation of iodine in
salt, STK method has a high sensitivity
but low specificity. These findings suggest that STK method can be used for
semi-quantitative estimation of iodine by the government and non-government
functionaries. The findings of the present study recommend that STK method can
be utilized as a semi-quantitative method for assessment of iodine content of
salt only for the purpose of monitoring the quality of salt available to the
community.
It
is further recommended that for monitoring the quality of iodised salt
available to the community members, it is necessary to analyze a large number
of salt samples to visualize the trend. In this context, the STK can prove a
simple and useful tool as compared to IT which requires laboratory facilities.
Table 1
Total
Number of Salt Samples Analysed at Different Centres
|
Centre |
No. of Salt Samples |
Type of
Salt Sample |
|||
|
Powdered
n (%) |
Crystalline
n (%) |
||||
|
|
700 |
684 |
(98.0) |
16 |
(2) |
|
|
700 |
576 |
(82.3) |
124 |
(17.2) |
|
Dehradun |
797 |
422 |
(52.9) |
375 |
(47.1) |
|
Jhansi |
855 |
364 |
(42.6) |
491 |
(57.4) |
|
Kangra |
746 |
746 |
(100.0) |
0 |
(0.0) |
|
(IHE) |
887 |
887 |
(100.0) |
0 |
(0.0) |
|
Udham Singh Nagar |
736 |
676 |
(91.8) |
60 |
(8.2) |
|
(AIIMS) |
881 |
764 |
(86.7) |
117 |
(13.3) |
|
Total |
6302 |
5119 |
(81.2) |
1183 |
(18.8) |
Table 2
Iodine Content of Salt by Iodometric Titration
Method at Different Centres
|
Centre |
<15
ppm |
15
ppm and More |
||
|
n |
% |
n |
% |
|
|
|
208 |
(29.7) |
492 |
(70.3) |
|
|
351 |
(50.1) |
349 |
(49.8) |
|
Dehradun |
302 |
(37.9) |
495 |
(62.1) |
|
|
461 |
(53.9) |
394 |
(46.1) |
|
Kangra |
49 |
(6.6) |
697 |
(93.4) |
|
|
455 |
(51.3) |
432 |
(48.7) |
|
Udham Singh
Nagar |
168 |
(22.8) |
568 |
(77.2) |
|
|
403 |
(45.7) |
478 |
(54.3) |
|
Total |
2397 |
(38.0) |
3905 |
(62.0) |
Table 3
Iodine Content of Salt by Iodometric STK Method
at Different Centres
|
Centre |
<15
ppm |
15
ppm and More |
||
|
n |
% |
n |
% |
|
|
|
234 |
(33.4) |
466 |
(66.6) |
|
|
365 |
(52.2) |
335 |
(47.8) |
|
Dehradun |
240 |
(30.1) |
557 |
(69.9) |
|
|
311 |
(36.4) |
544 |
(63.6) |
|
Kangra |
93 |
(12.5) |
653 |
(87.5) |
|
|
374 |
(42.2) |
513 |
(57.8) |
|
Udham Singh
Nagar |
117 |
(15.9) |
619 |
(84.1) |
|
|
239 |
(27.1) |
642 |
(72.9) |
|
Total |
1973 |
(31.3) |
4315 |
(68.7) |
Table 4
Iodine Content of Salt Samples by Both IT and STK
Methods at different Centres
|
Centre |
Salt
Iodine Content |
|||||||
|
a* |
b* |
c* |
d* |
|||||
|
n |
(%) |
n |
(%) |
(n) |
(%) |
(n) |
(%) |
|
|
(n=700) |
466 |
(66.6) |
00 |
(0.0) |
26 |
(3.7) |
208 |
(29.7) |
|
(n=700) |
284 |
(40.6) |
51 |
(7.3) |
65 |
(9.3) |
300 |
(42.8) |
|
Dehradun (n=797) |
472 |
(59.2) |
85 |
(10.7) |
23 |
(2.9) |
217 |
(27.2) |
|
(n=855) |
318 |
(37.2) |
226 |
(26.4) |
76 |
(8.9) |
235 |
(27.5) |
|
Kangra (n=746) |
629 |
(84.3) |
24 |
(3.2) |
68 |
(9.1) |
25 |
(3.4) |
|
(n=887) |
350 |
(39.5) |
163 |
(18.4) |
82 |
(9.2) |
292 |
(32.9) |
|
Udham Singh
Nagar (n=736) |
543 |
(73.8) |
76 |
(10.3) |
25 |
(3.4) |
92 |
(12.5) |
|
(n=881) |
443 |
(50.3) |
199 |
(22.6) |
35 |
(3.9) |
204 |
(23.2) |
|
Total (n=6302) |
3505 |
(55.6) |
824 |
(13.1) |
400 |
(6.3) |
1573 |
(25.0) |
a* = Iodine content 15
ppm and more by IT method as well as STK method
b* = Iodine content
less than 15 ppm by IT method but 15 ppm and more by STK method
c* = Iodine content 15
ppm and more by IT method but less than 15 ppm by STK method
d* = Iodie content less
than 15 ppm by IT method as well as STK method
Table 5
5.1 Sensitivity and Specificity of STK against IT
method at Baroda Centre
Principal Investigator
: Prof. S. Seshadri
Head,
Deptt. of Fods & Nutrition
Faculty
of Home Science
Baroda-390002.
Sensitivity and
Specificity of STK against IT method
(n=700)
Titration Method
|
|||
|
STK Method |
15 ppm & more |
<15 ppm |
Total |
|
15 ppm & more |
466 |
0 |
466 |
|
<15 ppm |
26 |
208 |
234 |
|
Total |
492 |
208 |
700 |
Sensitivity = 466/492 X100 = 94.7%
Specificity = 208/208 X 100 = 100.0%
Positive Predictive Value = 466/466 X 100 = 100.0%
Negative Predictive Value = 208/234
X 100 = 88.1%
5.2 Sensitivity and
Specificity of STK against IT method at
Principal Investigator : Dr.
S.S. Swami
Deptt.
of Preventive and Social Medicine
Sensitivity and Specificity of STK against IT method
(n=700)
Titration Method
|
|||
|
STK Method |
15 ppm & more |
<15 ppm |
Total |
|
15 ppm & more |
284 |
51 |
335 |
|
<15 ppm |
65 |
300 |
365 |
|
Total |
349 |
351 |
700 |
Sensitivity = 284/349 X 100 = 81.4%
Specificity = 300/351 X 100 = 85.5%
Positive Predictive
Value = 284/335 X 100 = 64.8%
Negative Predictive
Value = 300/365
X 100 = 82.2%
5.3 Sensitivity and
Specificity of STK against IT method at Dehradun
Centre
Principal Investigator : Ms.
Beena
Mamta
Samajik Sanstha
UNICEF
Sponsored Programme
S3-
Dehradun-248001
Sensitivity and Specificity of STK against IT Method
(n=797)
Titration Method
|
|||
|
STK Method |
15 ppm & more |
<15 ppm |
Total |
|
15 ppm & more |
472 |
85 |
557 |
|
<15 ppm |
23 |
217 |
240 |
|
Total |
495 |
302 |
797 |
Sensitivity = 472/495 X 100 = 95.4%
Specificity = 217/302 X 100 = 71.8%
Positive Predictive
Value = 472/557 X 100 = 84.7%
Negative Predictive
Value = 217/240
X 100 = 90.4%
5.4 Sensitivity
and Specificity of STK against IT method at
Principal Investigator : Dr.
B.P. Mathur
Reader, Deapartment
of PSM,
Sensitivity and Specificity of STK against IT
method
(n=855)
Titration Method
|
|||
|
STK Method |
15 ppm & more |
<15 ppm |
Total |
|
15 ppm & more |
318 |
226 |
544 |
|
<15 ppm |
76 |
235 |
311 |
|
Total |
394 |
461 |
855 |
Sensitivity = 318/394 X 100 = 80.7%
Specificity = 235/461 X 100 = 50.9%
Positive Predictive
Value = 318/544 X 100 = 58.4%
Negative Predictive
Value = 235/311 X 100 = 75.6%
5.5 Sensitivity and Specificity of STK against IT method at
Kangra Centre
Principal Investigator : Dr.
T.D. Dharma
Principal
Health & Family
Welfare Centre
Kangra- 176001
Sensitivity and Specificity of STK against IT
method
(n=746)
Titration Method
|
|||
|
STK Method |
15 ppm & more |
<15 ppm |
Total |
|
15 ppm & more |
629 |
24 |
653 |
|
<15 ppm |
68 |
25 |
93 |
|
Total |
697 |
49 |
746 |
Sensitivity = 629/697 X 100 = 90.2%
Specificity = 25/49 X 100 = 51.0%
Positive Predictive
Value = 629/653 X 100 = 96.3%
Negative Predictive
Value = 25/93 X 100 = 26.8%
5.6 Sensitivity
and Specificity of STK against IT method at
Principal Investigators: Dr. Kumud Khanna
and Dr. Amita Attle
Department
of Foods and Nutrition,
Institute
of Home Economics (IHE),
New
Delhi
Sensitivity and Specificity of STK against IT
method
(n=887)
Titration Method
|
|||
|
STK Method |
15 ppm & more |
<15 ppm |
Total |
|
15 ppm & more |
350 |
163 |
513 |
|
<15 ppm |
82 |
292 |
374 |
|
Total |
432 |
455 |
887 |
Sensitivity = 350/432 X 100 = 81.0%
Specificity = 292/455 X 100 = 64.2%
Positive Predictive
Value = 350/513 X 100 = 68.2%
Negative Predictive
Value = 292/374 X 100 = 78.1%
5.7
Sensitivity and Specificity of STK against IT method at
Udham Singh Nagar Centre
Principal Investigator
: Dr. R.S. Raghuvanshi
Reader, Deptt. of Foods &
Nutrition
GB Pant
and Technology,
Pantnagar, Udham Singh
Nagar-263145
Sensitivity and Specificity of STK against IT
method
(n=736)
Titration Method
|
|||
|
STK Method |
15 ppm & more |
<15 ppm |
Total |
|
15 ppm & more |
543 |
76 |
619 |
|
<15 ppm |
25 |
92 |
117 |
|
Total |
568 |
168 |
736 |
Sensitivity = 543/568 X 100 = 95.5%
Specificity = 92/168 X 100 = 54.7%
Positive Predictive
Value = 543/619 X 100 =
87.7%
Negative Predictive
Value = 92/117
X 100 = 78.6%
5.8 Sensitivity and Specificity of STK against IT method at
Principal Investigator : Dr. Umesh Kapil
and Dr. S.N. Dwivedi
Additional
Professor,
Department
of Human Nutrition and
Biostatistics,
All
India Institute of Medical Sciences,
Ansari
Nagar, New Delhi-110029
(n=881)
Titration Method
|
|||
|
STK Method |
15 ppm & more |
<15 ppm |
Total |
|
15 ppm & more |
443 |
199 |
642 |
|
<15 ppm |
35 |
204 |
239 |
|
Total |
478 |
403 |
881 |
Sensitivity = 443/478 X 100 = 92.7%
Specificity = 204/404 X 100 = 50.5%
Positive Predictive Value = 443/642 X
100 = 69.0%
Negative Predictive Value = 204/239 X 100 = 85.3%