Vol. 52, No. 4
Printed in U.S.A.
T H E AMERICAN JOURNAL OF CLINICAL PATHOLOGY
Copyright © 1969 by The Williams & Wilkins Co.
PERFORMANCE OF " K I T S " USED FOR CLINICAL CHEMICAL
ANALYSIS OF GLUCOSE
ROY N. BARNETT, M.D., AND ANN D. CASH, MT (ASCP)
Division of Laboratories, Norwalk Hospital, Norwalk, Connecticut 06852
ABSTRACT
Barnett, Roy N., and Cash, Ann D.: Performance of "kits" used for clinical
chemical analysis of glucose. Am. J. Clin. Path., 52: 457-465,1969. Comprehensive studies were performed on 17 "kits" for glucose analysis on the market in
June 1967. These included reproducibility studies of aqueous solutions at three
levels, reproducibility studies of serum pools at three levels, recovery studies, and
50 patient comparisons using the AutoAnalyzer ferricyanide method for reference.
Operator bias was eliminated by performing all calculations after the experiments
were complete. Five of the kits were found to be satisfactory by arbitrary
performance criteria and 12 were not.
In the first article in this series,3 we
evaluated "kits" used for cholesterol analyses of blood, following a scheme previously
published.1 We found that many of the kits
did not yield analytic results sufficiently
accurate to be medically useful. We demonstrated the feasibility of studying a large
number of different kits concurrently and
established an appropriate protocol for collection of data in an efficient fashion.
Glucose was selected for our second study
because there are many glucose kits in use
and because glucose analyses are of great
clinical importance.
M A T E R I A L AND METHODS
In March 1967, we found 16 glucose kits
advertised in medical or laboratory journals
and, in June 1967, one more appeared and
was incorporated in the study. We purchased the materials through distributors
when possible; otherwise, we got them from
the manufacturer. Depending upon the
number of tests which could be performed
with one set of reagents, we bought from
Received November 11,1968; accepted for publication May 13, 1969.
The research upon which this publication is
based was performed pursuant to Contract FDA
67-44 with the Food and Drug Administration,
Department of Health, Education, and Welfare.
This report reflects the opinion of the authors and
not necessarily that of the Food and Drug Administration.
457
one to four individual packages, usually at
the same time. As the materials were received, each was assigned a letter. Table 1
lists by assigned letter the catalog name and
manufacturer of each kit and the type of
reaction employed.*
As a reference method we chose the AutoAnalyzer ferricyanide method.6 Although
this is not absolutely specific for glucose,
"specificity of the chemical system is about
the same as the combined zinc hydroxide
precipitation and oxidation-reduction color
reaction of the Somogyi-Nelson method." 4
In addition, this is a very widely used technic with satisfactory precision. All other
methods were performed exactly as specified
by the manufacturer and we made no attempt to alter or improve any procedure.
For all spectrophotometric readings except Method L, the Coleman Jr. Spectrophotometer Model 6A was utilized. For
Method L, the distributor provided the UniMeter instrument. When possible, the Gilford Model 300 spectrophotometer was
used in parallel with the Coleman Jr. Comparative results with these two instruments
will be reported elsewhere but we can state
that the results were essentially identical.
Method 0 depends on visual color comparison and is semiquantitative. Results with
this method are included in all of our tables
but are discussed separately. Standard
* Some of these methods have been abandoned or
changed since the time that we purchased the kits.
45S
BARNETT AND CASH
TABLE 1
IDENTIFICATION OF GLUCOSE K I T S
Letter
Catalog NTame and
Manufacturer
B
Glucose Set
Medi-Chem, Inc., S a n t a
Monica, Calif.
Hyland Glucose T e s t
Hylancl Laboratories,
Los Angeles, Calif.
Hycel P-M-S
Hycel, Inc., Houston, Tex.
c
D
E
F
G
H
I
J
K
L
M
N
0
P
Q
R
Harleco Glucose
H a r t m a n - L e d d o n C o . , Inc.,
Philadelphia, P a .
Glucose T e s t
Chem-Stat, Inglewood,
Calif.
Sigma Glucose
Sigma Chemical Co.,
St. Louis, Mo.
Blood Sugar
Boehringer-Mannheim,
Biochemical Division
New York, N . Y.
Glucose Set 650-12
National
Bio-Technical
Lab., Seattle, Wash.
Hoppers Glucose-enzyme
Hoppers L a b . , Inc., H o u s ton, Tex.
Gluco-Pak
Uni-Tech, P a n o r a m a City,
Calif.
Glucose Uni-Test
Bio-Dynamics, I n c . , Indianapolis, Ind.
Glucostat
Worthington Biochemical
Corp., Freehold, N . J.
Hycel Carbohydrate
Hycel, Tnc. Houston, Tex.
Dextrostix
Ames Company, E l k h a r t ,
Ind.
T r u e Glucose Set
Medi-Chem, Inc., S a n t a
Monica, Calif.
M a u r u k a s Glucose
Maurukas
Company,
Elyria, Ohio
Glytel
Pfizer Diagnostics, New
York, N . Y.
Chemical
Procedure
Folin-Wu
Oxidase
method
Phenol in
methjd
salicylate
orthoToluidine
Enzyme
method
SomogyiNelson
o-Dianisidine
hydrochloride and
phosphate
buffer
Folin-Wu
Enzyme
reaction
orthoToluidine
Oxidaseperoxidase
Oxidaseperoxidase
Seliwanoff
Oxidase and
chromogen
Modified
Folin-Wu
orlhoToluidine
orthoToluidine
Vol. 52
volumetric pipettes were used except for
methods in which capillary pipettes were
supplied by the manufacturer and Methods
P, N, and Q for which a special dispenser
was obtained from the manufacturer.
Statistical analyses were performed as
previously described,1 with the following
exceptions. First, we considered values to be
outliers only when both statistical and collateral data indicated a high probability of
a technical error. Second, we found that our
earlier recommendation for setting of precision limits derived from repeated analyses
of pure aqueous solutions was unwarranted.
Some methods perform very differently
when aqueous solutions are compared with
serum pools, and it is the latter which are
pertinent to clinical analyses.
Reproducibility studies were performed in
two ways. First, we used aqueous standard
glucose solutions containing 40 mg. per 100
ml., 90 mg. per 100 ml., and 200 mg. per
100 ml. of Baker's dextrose meeting American Chemical Society specifications. Benzoic
acid, 0.2%, was used as a preservative and
the solutions were kept refrigerated when
not in use. For Methods P and N, the pure
dextrose was made up in tungstic acid solution as recommended by the manufacturer.
Each solution was tested by each method
once a day until from 10 to 14 analyses were
completed. Because there were so many
methods, not all 17 could be performed each
day. The order of performance was varied
randomly with some effort to perform each
method sometimes in the morning and sometimes in the afternoon. The spectrophotometric readings were recorded at once, but
no attempt was made to calculate the results
until all analyses were completed. This was
done to avoid possible operator bias. The
first 10 values for each method were used
for calculation unless there was substantial
reason to believe that a technical error had
been made, in which case the value was discarded and the 11th value used in its place.
A second set of reproducibility studies
was made, using serum pools. The pools were
made from a large frozen serum pool containing about 90 mg. per 100 ml. of glucose.
To prepare a low pool (about 40 mg. per 100
ml., of glucose), the original pool was diluted
with serum albumin. To prepare a high pool,
Oct. 1969
"KITS" FOR ANALYSIS OF GLUCOSE
suitable proportions of the original pool
were mixed with a reconstituted commercial
high glucose lyophilized material; the final
concentration was approximately 175 mg.
per 100 ml. by analysis. These three pools
were divided into small tubes which were
then refrozen until use. One of these tubes
was analyzed for each of 10 days at the same
time that the patients' samples were analyzed by the same methods.
Recovery studies were performed by using
a serum pool whose value was 84 mg. per
100 ml. by analysis, using the reference
method. To this we added suitable amounts
of a 400 mg. per 100 ml. aqueous solution
of dextrose, calculated to raise the level by
20% (16.8 mg.), 50% (42 mg.), and 100%
(S4 mg.). These three solutions and the base
material were each analyzed in triplicate in
a single day, by both the reference and the
test method. The recovery for each method
was calculated as the amount found by subtracting the base value for the method from
the value for each of the three solutions, and
also as percentage recovered of the calculated addition. The average of the triplicate analyses was used in each case.
RESULTS
Reproducibility Studies
We found no evidence of spoilage of reagents, glucose solutions, or serum pools in
these experiments. Tables 2, 3, and 4 are
arranged in ascending order of the mean
values for the aqueous standards. Each
table lists results from 10 consecutive oncea-day analyses, indicating mean value, 1
S.D., and coefficient of variation
( i £ x *>)
The level for the aqueous standards indicates the known weight of pure dextrose in
water. The level of each serum pool is the
mean value of 20 reference analyses. The
reference method values are italicized. Inspection of these tables indicates, among
other facts, the sometimes marked discrepancy between values for aqueous and
serum analyses by the same method. The
same data, for serum pools only, are portrayed more vividly in Figures 1, 2, and 3.
459
Recovery Studies
Table 5 lists the recovery studies for each
method, indicating the percentage of glucose recovered. Italicized values differ from
the expected value by more than 1.63 S.D.
for the method calculated from the serum
pool precision studies. These values are considered to be unacceptable. The 1.63 S.D.
figure represents the standard deviation of
the pool (calculated from single observations) times v / 2/"V / 3 because we compare
two different methods and perform each of
them in triplicate; this result is multiplied
by two to give 95 % confidence limits.
In order to illustrate this calculation, we
take the following example from the kit B
studies. The serum pool was analyzed in
triplicate by Method B, yielding values of
79, 88, and 99 mg., average SS.7. The spiked
pools were also analyzed in triplicate, the
values for the high pool being 175, 179, and
1S4 mg., average 179.3. The difference between the high pool and the original pool is,
therefore, 90.6 mg., which is 6.6 mg. less
than the expected difference of S4.0 mg.
based on the addition of pure glucose. The
actual analysis was performed at a level of
179.3 mg., which is very close to the 174.6
mg. of the high reproducibility pool. We
therefore compare the 6.6-mg. discrepancy
with 1.63 times the 15.8S mg. S.D. of the
high serum pool. The discrepancy could be as
high as 1.63 X 15.88 or 25.SS mg. without
being excessive. The value 6.6 mg. is therefore satisfactory.
It should be noted that the less precise
methods are not expected to yield as good
recoveries as the more precise ones. For
methods with very poor precision, the recovery experiments, therefore, do not provide any additional information.
Comparisons of Patients
This portion of the evaluation was concerned with performance of the kits on individual patient's specimen. We first divided the kits into two groups for technical
convenience. Methods requiring filtrates
were placed together and those using serum
were put in a separate group. One method,
G, required anticoagulated whole blood; for
this method the patients' samples used on
the AutoAnalyzer were also whole blood.
TABLE 2
R E P R O D U C I B I L I T Y S T U D I E S U S I N G A Q U E O U S STANDARDS AND P O O L E D S E R U M
Low Level
Method
p
L
G
R
E
K
F
AA (Ref.)
H
0
M
Q
c
N
B
D
J
I
Aqueous standard (40 mg.)*
Serum pool (45.6 mg .)*
Meant
S.D.t
C.V.
Meant
S.D.t
C.V.
33.7
35.1
35.9
38.4
38.8
39.1
39.9
41.5
41.8
42.0
42.6
42.6
43.5
43.9
45.3
50.1
53.2
68.4
7.01
4.98
3.35
2.37
1.75
11.31
4.91
2.72
6.18
1.97
3.69
4.27
10.01
3.00
3.43
3.28
5.71
3.41
%
20.80
14.18
9.33
6.17
4.51
28.92
12.30
6.55
14.78
4.69
S.66
10.02
23.00
6.83
7.57
6.54
10.73
4.98
33.6
30.5
37.4
37.2
18.4
12.2
33.4
45.6
34.2
42.4
42.2
51.9
49.8
41.2
45.8
42.1
36.3
71.2
4.77
3.81
2.95
3.36
4.14
6.39
S.53
5.40
S.4S
2.99
4.15
11.08
9.47
4.52
4.68
5.67
8.S2
15.25
%
14.19
12.45
7.88
9.03
22.50
52.37
25.53
11.84
24.79
7.05
9.83
21.34
19.01
10.97
10.21
13.46
24.29
21.41
* N = 10.
t Mean and s t a n d a r d deviation reported in milligrams per 100 ml.
TABLE 3
R E P R O D U C I B I L I T Y S T U D I E S U S I N G A Q U E O U S STANDARDS AND P O O L E D S E R U M
Medium Level
Method
K
P
E
G
L
F
R
Q
C
J
AA (Ref.)
M
H
O
N
D
B
I
Aqueous standard (90
Serum pool (87.4 mg
Tig-)*
)*
Meant
S.D.t
C.V.
Meant
S.D.t
C.V.
73.3
81.1
84.2
86.1
87.3
88.0
SS.2
S8.2
S9.5
S9.8
90.2
90.3
90.4
92.2
94.0
97.2
9S.3
98.8
8.68
5.92
1.93
2.02
4.72
6.13
4.47
7.76
7.95
5.81
2.90
6.24
5.92
1.84
5.98
4.87
4.85
4.96
%
11.84
7.29
2.29
2.34
5.40
6.96
5.06
8.79
8.88
6.46
3.21
6.91
6.54
1.99
6.36
5.01
4.93
5.02
25.2
78.9
58.6
88.4
73.2
76.1
84.2
102.2
83.4
71.2
87.4
86.3
75.0
94.3
92.1
92.3
98.9
91.8
3.39
10.86
12.96
4.86
11.17
17.30
3.49
37.25
9.75
18.61
7.21
9.96
11.11
3.02
6.66
13.12
5.11
18.68
%
13.45
13.76
22.11
5.49
15.25
22.73
4.14
36.44
11.69
26.13
8.06
11.54
14. SI
3.20
7.23
14.21
5.16
20.34
* JV = 10.
t Mean and s t a n d a r d deviation reported in milligrams per 100 ml.
460
Oct. 1969
461
"KITS" FOE ANALYSIS OF GLUCOSE
TABLE 4
REPRODUCIHILITY STUDIES USING AQUEOUS STANDARDS AND POOLED SERUM
High Level
Method
Aqueous standards (200 mg.)*
Serum pool (174.6 mg.)*
Meanf
S.D.t
C.V.
141.6
179.2
179.5
183.7
184.3
192.1
195.2
198.2
200.5
200.6
202.9
203.1
203.8
206.6
207.8
210.0
211.7
216.2
23.03
12.39
7.71
5.66
11.73
22.87
8.11
23.65
22.82
5.72
13.67
12.18
7.54
7.31
3.81
11.21
5.62
15.45
16.26
6.91
4.29
3.08
6.36
11.90
4.15
11.93
11.38
2.85
6.73
5.99
3.69
3.53
1.83
5.33
2.65
7.14
Meant
S.D.t
C.V.
113.3
137.8
156.9
131.0
140.3
176.8
176.1
49.6
208.7
174-6
168.1
170.4
139.6
169.9
197.3
184.8
167.4
165.0
36.89
24.73
9.18
21.36
34.69
21.81
S.60
S.90
63. S4
9.54
S.76
16.26
21.10
16.01
4.85
15.88
19.94
20.5S
32.55
17.94
5.85
16.30
24.72
12.33
4.88
17.94
30.5S
5.46
5.21
9.54
15.11
9.42
2.45
8.59
11.91
12.47
%
J
I
M
B
C
F
G
K
Q
AA (Ref.)
R
P
L
N
0
B
D
H
%
* N = 10.
t Mean and standard deviation reported in milligrams per 100 ml.
Method O was performed on drops of whole
blood. Each day we selected five patients
whose physicians had requested analyses for
blood glucose. We drew 10 ml. of blood in
plain Vacutainers, and for Method G, an
additional ethylenediaminetetracetic acidfluoride tube was used. The serum was
separated promptly and filtrates were made
at once. Serum that was to be used whole
was refrigerated until the testing was begun.
Samples from five patients were analyzed
each day on 10 successive days for each kit,
a total of 50 patient samples each. As described above, the same patient sample
was subject to analysis by eight or nine kits,
depending on M'hich group was under study
at the time. In addition, we ran the reference
method on each sample. We also carried the
three serum pools along with 10 of the patient studies. Finally, we froze sera from the
first 20 patients in the first group and analyzed them by the reference and several
kit methods in the second group. The
spectrophotometric readings were recorded
promptly but the results were not calculated
until all of the analyses for the group were
completed.
Table 6 indicates the difference in milligrams from the reference method for each
kit for serum pools and patient studies. A
plus sign is obtained if the kit value is
larger and a minus sign if the lcit value is
smaller. The methods are arranged in order
of ascending total difference from the reference values, calculated by adding the three
difference figures for the serum pools, omitting the signs. In the patient studies, only
medium (up to 121 mg.) and high (127 mg.
and above) are present because we did not
encounter any low values in the patient
studies.
In the final table, Table 7, the standard
deviation of the differences between the
reference and test method in the patient
comparisons is enumerated in the column
labeled Patient S.D.f Additional statistical
t The raw material for this study is too voluminous for publication here. It is on file with the
Food and Drug Administration, Washington, D. C.
462
Vol. 52
BARNETT AND CASH
Low (45.6mg) Serum Glucose
Mean + 3S.D.
400 r
I
r ig h (174.6 mg ) Serum Glucose
Mean + 3 S.D.
360
•
Q
C
mg/
100 ml
II
jr..
J
s
111
I
fe
•
H
M
i|S
J1
AA R
n
W:
W
111:
m
1
ill
_J
Order of Ascending Means
F I G . 1. Low serum pool. E a c h 6a?' represents
results for the method designated by the letter
above it. In each bar, t h e middle horizontal line
is the m e a n ; the upper and lower lines are 3 S.D.
limits. M e a n and S.D. are derived from once-aday analyses for 10 days for each method. T h e
uniform
cross-hatched
horizontal area includes
99.73% of t h e values obtained b y t h e reference
method. Methods are arranged from left to right
in order of ascending means.
Medium (89.4 mg) Serum Glucose
Mean + 3 S. D.
mg/
100 ml
C
[i
mg/
100 ml
;::::::::
i
:::::::::
•
K
I
I
F
H D
—|—1
pi.
n
\
\
-
N P
„rT~kAG
nt
5i Li iji 5
3
i
Order of Ascending Means
F I G . 3. High serum pool. Arranged as in Figure 1
did not calculate "large discrepancies." We
decided that outliers identified in this
fashion are not meaningful. We used all of
the data except for a few results which we
believed, on the basis of collateral information, represented errors of technic or transcription not reasonably assignable to
problems with the test method.
Method 0
Order of Ascending Means
F I G . 2. Medium serum pool. Arranged as in
Figure 1.
manipulations were performed as described
previously. These indicated that there was
reagent deterioration of some kits, namely,
E, I, and J. For some of these, we had made
reagents in batches calculated to last several
days when the directions stated that this
was appropriate, but it was evident that the
mixed reagents were not stable.
In contrast to our cholesterol studv, we
This is a semiquantitative method which
specifically is "not intended to replace the
more precise analytic procedures where exact
blood glucose quantitation is required."!
Although the color chart is divided into
rather large increments of 20 to 50 mg., it is
relatively easy to interpolate and we did
attempt exact readings by this method. In
inspecting the data, it will be noted that this
method performed well except in two areas.
One was the high value in the serum studies,
and this is meaningless because the product
should not be used for serum analysis.
The other is the low value in the high
range of patient comparisons, and this is in
accord with the manufacturers' warning that
"values in this range tend to be lower than
J Instructions with the method.
Oct. 1969
463
"KITS" FOR ANALYSIS OF GLUCOSE
TABLE 5
TABLE 6
RECOVERY STUDIES FOR PERCENTAGE OF GLUCOSE
COMPARISON WITH REFERENCE METHOD VALUES
Method
+20%
(16.8 mg.)*
+50%
(42 mg.)*
+100%
(84 mg.)t
Serum Pools
Kit
Ref.
B
C
D
E
F
G
H
[
J
K
L
M
N
0
P
Q
R
89
155
89
190
42
36
113
77
83
65
71
89
71
172
77J
107
119
107
90
117
83
12S
64
33
117
100
SI
50
62
95
45
128
90t
67
166
95
99
107
76
116
71
36
112
107
6S
44
U
99
65
119
89%
S9
182
104
* For first two columns, acceptable if inside
±1.63 S.D. for medium level pool.
f For third column, acceptable if inside ±1.63
S.D. for high level pool. Italicized, not acceptable.
t Semiquantitative method.
those obtained by standard procedures."
We may summarize by saying that, within
those limitations spelled out by the producer, this method performs as well as the
quantitative technics.
DISCUSSION
Criteria for Performance
In order to establish the over-all performance of each kit, it is necessary to set
up some sort of criteria, and this must be
arbitrary indeed. Both precision (reproducibility) and accuracy (difference from
the reference method value) must be considered. Precision should be such that patient values will be reproducible within useful clinical limits. Accuracy should be
sufficient that patient values will not be
greatly different from those determined by
standard methods. Both precision and accuracy should be greatest at decision levels.
We have discussed this whole subject at
some length previously.2 In the present
Low
(45.6)
Medium
(89.4)
Patient Studies
High
(174.6)
Medium
(to 122)
High
(above 127)
mg./lOO ml.
G
N
D
R
B
M
P
F
0*
H
C
I
Q
L
E
J
K
-S.l
-4.3
-3.4
-8.3
+0.3
-3.3
-11.9
-12.1
-3.1
-11.3
+4.3
-9.2
+6.4
-15.0
-27.1
+25.7
-33.3
-1.0
+ 1.5
+2.7
-4.7
+2.9
-7.2
-5.2
-6.5
+9.5 +10.2
- 3 . 1 -17.7
-10.5
-4.2
+2.2
-13.3
+4.9 +22.7
-14.4
-9.6
- 6 . 0 -34.3
+2.4 -36.S
+12. S +34.1
-16.2 -35.0
-30.S -43.6
-18.2 -61.3
- 6 4 . 2 -125.0
+6.0
+5.1
-1.9
+6.7
-4.1
+ 7.S
-10.0
-2.S
+5.S +20.5
- 7 . 2 -26.5
-10.2
-3.0
+4.7
-5.S
- 5 . 9 -36.6
-10.9 - 1 0 . 0
-18.4 -43.4
+2.0 -40.S
+30.2 +20. S
-23.9 - 2 6 . 4
-33.S - 4 9 . 3
- 3 0 . 2 -120.0
-69.7 -120.3
* Semiquantitative method.
context we also consider "state of the art."
There are good, simple, glucose methods,
some of which form the basis for some of the
kits that we studied. We can therefore insist that a useful method for glucose determination must furnish data not appreciably worse than conventional technics
which could be used in similar circumstances.
Certainly it would be unreasonable to require automated machinery in small laboratories. However, it is not unreasonable
to expect these small laboratories to provide
results of analyses that are as medically useful as is possible with ordinary skill and
equipment.
Bearing in mind these factors, we set up
the following arbitrary criteria, all applicable to Table 7.
1. Precision (coefficient of variation).
A. Good (G). Coefficient of variation does
not exceed 1.5 times that of reference
method.
B. Acceptable (A). Coefficient of variation exceeds 1.5 but not 2.0 times that for
reference method.
C. Not acceptable (Ar). Coefficient of vari-
464
BARNETT AND CASH
Vol. 52
TABLE 7
OVERALL PERFORMANCE OP " K I T S " *
Ac ueous S.D.
serum S.D.
Aqueous Bias
Serum Bias
Patient S.D.
Patient Bias
Med.
High
A
N
G
N
A
A
N
G
N
N
N
A
G
A
N
N
A
N
N
G
N
G
G
A
N
N
N
N
N
G
Nt
G
N
G
Kit
Low Med.
Bj
C
D
E
F
Gt
II
I
J
K
L
M
Nt
Of
P
Q
Rt
G
N
G
G
A
G
N
G
A
N
N
G
G
G
N
A
G
A
N
A
G
N
G
N
A
N
N
A
N
A
G
N
N
A
High Low Med. High
A
N
G
G
N
G
N
N
N
N
G
G
G
G
N
N
N
A
G
N
G
G
G
G
N
N
G
G
G
G
G
A
G
G
A
G
A
A
G
G
G
A
G
N
G
G
G
G
A
G
G
G
N
A
N
G
G
N
N
N
G
G
N
G
G
G
G
G
Low Med. High
G
A
G
A
N
G
N
A
N
N
G
G
G
G
G
A
G
G
G
A
N
N
G
A
N
N
A
A
G
G
G
A
N
G
A
N
N
N
N
G
N
N
N
N
N
G
A
G
A
N
G
Low
Med.
High
Med.
High
G
G
G
N
N
A
N
N
N
N
N
G
G
G
N
A
A
A
A
G
N
N
G
N
G
N
N
N
G
G
G
N
N
A
A
N
G
N
G
G
G
N
N
N
N
N
G
Nt
G
N
G
8.27
18.65
12.23
11.97
14.93
15.10
14.48
24.98
18.98
9.13
8.32
10.61
17.24
18.28
15.46
26.74
6.39
14.24
40.18
22.63
21.72
22.46
34.05
14.20
44.55
S2.47
27.36
10.49
20.24
20.78
24.58
18.58
53.44
18.56
Recovery
A
A
A
A
N
A
A
A
A
N
A
N
N
Nt
A
A
A
* G = good, A = acceptable, N = not acceptable; definitions in text,
f Overall performance satisfactory,
t Not meaningful. See text.
ation exceeds 2.0 times that for reference
method.
2. Accuracy (bias), applicable to aqueous
pools, serum pools, and patient comparisons.
A. Good ((?). Bias does not exceed 5 mg.
in low or medium range, or 10 mg in high
range.
B. Acceptable (A). Bias exceeds 5 mg. but
not 10 mg. in low or medium range; exceeds
10 mg. but not 15 mg. in high range.
C. Not acceptable (N). Bias exceeds 10 mg.
in low or medium range, exceeds 15 mg. in
high range.
3. Standard deviation of difference in patient studies. We list the exact figures because we have no set idea on acceptable
levels. The smaller the figure the closer the
test method will come to the reference
method; 68% of values on the same specimen by the test and reference methods will
agree within the numerical limits listed.
4. Recovery.
A. Acceptable (A). Observed difference
after pure glucose is added within 1.63 S.D.
of expected difference at all three levels.
B. Not acceptable (N). Observed difference after pure glucose is added not within
1.63 S.D. of expected difference at any of
the three levels.
A logical question is the validity or fairness of conclusions reached by testing small
numbers of individual packages. We assume that products used in patient care
should exhibit uniformity of performance so
that our sampling is reasonable. To study
more packages would require more time and
personnel than we had at our disposal. As it
was, one technologist spent 2 months in the
chemical manipulations and more than 4
months for statistical processing.
One purpose of this study was to evaluate
the feasibility of testing kits on a comprehensive basis. The scheme,1 as modified in
this study, proved practical but requires a
vast amount of arithmetic. A desk calculator
with a moderate capacity to be programmed
§ Somewhat similar studies of N were carried out
by an independent evaluator for the College of
American Pathologists in 1965. The present results
are not greatly different from those results.
Oct. 1969
" K I T S " FOR ANALYSIS OK GLUCOSE
(Monroe Calculator Model Epic 2000)
saved a great deal of time compared to
simpler calculators; however, the statistics
could readily be completely computerized
with much greater saving of time and we
hope to arrange this in the future.
Conclusions
Method G was acceptable or good in all
categories; however, the standard deviation
of the differences is larger than that for some
of the other methods.
Method R was acceptable or good in all
categories except the high aqueous standard
precision, and this is not significant for patient studies. The standard deviation of the
difference from the reference method in the
low range is the smallest of any found.
Method N§ was good or acceptable in all
categories except the recovery in the low
range, and we believe that this is not of
major importance.
Method B was good or acceptable in all
categories except for a substantial tendency
to read high in the upper level of patient
465
studies, and some evidence of reagent deterioration. The standard deviation of the
differences was among the lowest found.
"Method 0 , a semiquantitative method,
ranged acceptable or good in all pertinent
categories.
All of the other methods fell significantly
short of meeting our criteria for acceptability.
Acknowledgments. W . J . Youden, P h . D . , served
as statistical consultant, and Morris Goldberg,
P h . D . , as the biochemical consultant.
REFERENCES
1. B a r n e t t , R. N . : A scheme for the comparison
of q u a n t i t a t i v e methods. Am. J. Clin.
P a t h . , 43: 5G2-5G9, 1965.
2. B a r n e t t , R. N . : Medical significance of laboratory results. Am. J. Clin. P a t h . , 50: 071G76, 1968.
3. B a r n e t t , R. N . , Cash, A. D . , and Junghans,
S. P . : Performance of " K i t s " used for clinical
chemical analysis of cholesterol. New England J. Med., 279: 974-979, 196S.
4. Glucose. Vol. 1. Technical Improvement Service. Chicago: American Society of Clinical
Pathologists, 1908.
5. Hoffman, W. S.: A rapid photoelectric method
for the determination of glucose in blood and
urine. J. Biol. Cheni., 120: 51-55, 1937.