Document 6428276

T E R S
Accuracy of Blood
Glucose Meters in
Pregnant Subjects
With Diabetes
I
t is essential for pregnant women with
diabetes to maintain a blood glucose
level as near to normal as possible to
improve perinatal outcome (1,2). Selfmonitoring of capillary blood glucose is
an important component of the management of blood glucose (3). However, a
report on four glucose meters cast doubts
on the accuracy of these devices in pregnant women with diabetes (4). We evaluated the accuracy and precision of the MediSense Precision QID, a new glucose
meter based on electrochemical biosensor
technology.
A total of 50 pregnant subjects
with diabetes participated in our study.
Their gestational ages ranged from 4 to 38
weeks. Of the subjects, 3,17, and 30 were
in their 1st, 2nd, and 3rd trimesters, respectively. A total of 6 subjects had
IDDM, 5 had NIDDM, and 39 had gestational diabetes. Analytical accuracy was
assessed by comparing capillary blood
glucose values between the Precision QID
and a laboratory method (the YSI glucose
analyzer). Two tests were performed with
the Precision QID and the YSI glucose analyzer on each subject. Precision was determined by calculating the mean of all
coefficients of variation (CVs) between the
duplicate measurements.
We found the accuracy of the Precision QID comparable with that of the
laboratory method; an error grid analysis
(5) of the 100 results is shown in Fig. 1.
Of the Precision QID results, 94 and
100% agreed within 15 and 20%, respectively, of the laboratory method values.
Linear regression analysis of the data
showed the following: correlation coefficient (r) 0.98, slope 1.03, intercept 1.0
mg/dl, Sy.x 8.2 mg/dl. The mean absolute
bias was 6.6%. The mean CV of paired
replicates was 3.5%, indicating good precision with the Precision QID.
It was suggested (4) that lower hematocrit levels and metabolic and physiological changes of pregnancy may interfere with the accuracy of glucose
reflectance meters; the levels of free fatty
acids, ketones, triglycerides, and cholesterol are increased in blood during pregnancy. Our data established that the Pre-
cision QID is accurate and precise for
monitoring glycemic control in pregnant
subjects with diabetes. The hematocrits of
the subjects in this study ranged from 30
to 47%, which is within the operating
specifications of the Precision QID. The
Precision QID test strip has a unique third
electrode specifically for canceling the effects of interferences from drugs and endogenous substances in the blood (6).
This additional electrode may contribute
to the accuracy of the Precision QID results in pregnant subjects.
In addition to accuracy, a glucose
meter for pregnant women who need frequent self-monitoring of blood glucose
should be easy to use and maintain. The
Precision QID meets this expectation. It
requires only a small drop of blood (5 /ml)
and 20 s for a test, with no test-strip
holder or optical window to clean. Besides the small sample-volume requirement, the Precision QID has a unique operating feature that allows the user to
apply another drop of blood within 30 s
to the same test strip if the first drop does
not start the test. Thus, it maximizes accuracy and the success rate of testing and
minimizes wastage of test strips due to
insufficient specimens.
PATRICIA STENGER, RN, CDE
MARY ELLEN ALLEN, RN
ouu -
LISA LISIUS, RN, CDE
X
500-
400 - -
x
E
in
©
a
3
a
o
§
300-
/
,
/
/
A/ A / AA
y/
A A A
/
c
on
a-
/ '
From the Eastern Maine Medical Center, Diabetes
Center, Bangor, Maine.
Address correspondence to Patricia Stenger, RN,
CDE, Eastern Maine Medical Center, Diabetes Center, 431 State St., Suite 4, Bangor, ME 04401.
/
A
A xX/
/
X
/
/ /
'XX
/A X
X
/
X
/
Acknowledgment—This study was supported in part by a grant from MediSense.
B
References
X B /X
/
/-/ y
200 -
.2
AS/
D
D
100A
/
r
r
/
00
100
By
A
/
1
200
300
400
YSI Mean Glucose, mg/dL
Figure 1—Error grid analysis oj 100 glucose results.
268
E
500
600
1. Karlsson K, Kjellmer I: The outcome of diabetic pregnancies in relation to the mother's blood sugar level. Am] Obstet Gynecol
112:213-220,1972
2. Fuhrmann K, Reiher H, Semmler K, Fischer F, Fischer M, Glochner E: Prevention
of congenital malformations in infants in
insulin dependent diabetic mothers. Diabetes Care 6:219-222, 1983
3. American Diabetes Association: Consensus
statement on self-monitoring of blood glucose. Diabetes Care 18:47-52, 1995
4. Harkness LJ, Ashwood ER, Parsons S,
Lenke RR: Comparison of the accuracy of
glucose reflectance meters in pregnant in-
DIABETES CARE, VOLUME 19, NUMBER 3 , MARCH
1996
Letters
sulin-dependcnt diabetics. Obstet Gynecol
77:181-185, 1991
'x Clarke WL, Cox D, Gonder-Frederick LA,
Carter W, Pohl SL: Evaluating clinical accuracy of systems for self-monitoring of
blood glucose. Diabetes Care 10:622-628,
1987
b. Ng RH, Martin L, Halpin M, Bernstein R,
Fischer J, Taylor E, Schroder S: Clinical
performance of a new test strip with the
MediSense blood glucose sensor. Clin
Chem 41 :S181, 1995
Sex Differences in
Plasma Glucose
Thresholds for
Counterregulatory
Hormone Release
and Hypoglycemia
Symptom Perception
S
ex has recently been identified as a
relevant factor in blood glucose
(BG) thresholds for cognitive-motor
dysfunction in adult IDDM patients (1,2)
and counterregulatory hormone secretion
in nondiabetic adults (3,4). These studies
suggest that males may be more sensitive
to low BG, both in terms of counterregulatory hormone secretion and cognitivemotor functioning. We attempted to replicate and extend these findings. We
reanalyzed data from a previous insulin
infusion study (5-7), comparing the BG
thresholds for counterregulatory hormone release and symptom perception in
adult IDDM subjects.
Of the adults with IDDM, 19 men
and 22 women were compared. Men and
women did not differ in terms of age
(33.2 ± 6.6 vs. 34.5 ± 9.2 years [means
± SD], NS), duration of disease (11.2 ±
10.9 vs. 14.2 ± 11.3 years, NS), daily insulin (.59 vs. .64 U/kg, NS), or HbAi
(12.2 ± 3 . 6 vs. 11.3 ±2.3,NS).
Intermediate and long-acting insulins were discontinued 48 h before testing, and overnight euglycemia was maintained at —5.6 mmol/1 with a previously
described open-loop insulin infusion algorithm (8,9). At 0800, the subjects were
connected to the Biostator glucosecontrolled insulin infusion system (Miles,
lilkhart, IN) for continuous glucose monitoring and insulin (human regular, Lilly,
DIABETES CARK, VOLUME 19,
NUMBER 3 ,
MARCH
Indianapolis, IN) infusion at the rate of 40
jLtmol • kg" 1 • h ~ \ The insulin infusion
was continued for 120 min.
Plasma was sampled every 10 min
for the determination of plasma glucose,
epinephrine, and glucagon. Plasma glucose was determined with a glucose oxidase method (Beckman glucose analyzer,
Fulton, CA). Plasma glucagon was determined by radioimmunoassay (10), and
plasma epinephrine concentration was
determined by a single-isotope derivative
method (11). Immediately before the 10min blood draws, subjects rated (0 =
none, 6 = extreme) five autonomic symptoms (trembling, pounding heart, sweaty,
cold hands, tense/frustrated) and five
neuroglycopenic symptoms (difficulty
concentrating, confusion, blurred vision,
slurred speech, numb lips).
Using the criteria of other published studies, the plasma glucose threshold level was defined as that at which
there was an unequivocal sustained increase in circulating epinephrine and glucagon or an increase in symptom ratings
above baseline level (3,6). For example, if
the plasma epinephrine fluctuated between 10 and 20 pmol/1 and epinephrine
rose to 81 pmol/1 at 70 min and to 96
pmol/1 at 80 min and sustained this elevation, the plasma glucose level at 70 min
would be identified as the threshold for
epinephrine release. This was done by
two examiners who were blind to the subject's sex. No plasma glucose thresholds
were found for hormones or symptoms
for three women and two men, i.e., they
did not counterregulate and were therefore not included in the data analysis.
Once BG thresholds for each hormone
and each symptom cluster were identified
for each subject, data were divided according to sex and analyzed with analysis
of variance.
Relative to the women, the men's
plasma glucose levels were significantly
higher for plasma epinephrine release
(3.2 ± 0.56 vs. 2.8 ± 0.49 mmol/1, P •• •
0.030) and plasma glucagon release
(2.9 ± 0.69 vs. 2.5 ± 0.39 mmol/1, P = =
0.04). However, there were no significant
differences between the men's and the
women's plasma glucose levels for initial
perception of either autonomic (2.9 :•:
0.7 vs. 3.0 ± 0.6 mmol/1) or neuroglycopenic symptoms (3.0 ± 0.7 vs. 3.1 :+: 0.8
mmol/1; Fig. 1).
These data are the only available
data on diabetic patients that confirm previous studies with nondiabetic subjects
demonstrating that men with IDDM respond with epinephrine and glucagon at a
higher plasma glucose level than do
women. This sex difference cannot be explained in terms of differential metabolic
control, since we found no difference in
HbAj. Also, it cannot be explained by a
differential rate of BG fall, since women's BG tended to fall faster (0.07
mmol • T ' • min [ ) than men's (,0.0'5
mmol • I" 1 • min" 1 , NS). Whether differential counterregulatory and cognitive responses are centrally or peripherally mediated is yet to be clarified. The
present data do not suggest that sex affects BG thresholds for the perception of
either autonomic or neuroglycopenic
symptoms. Clinically, this may reflect
an inherent danger for men. It is possible that men may experience hypoglycemia counterregulation and cognitive-
mM
3.5
•<.O4
3
2.5
2
1.5
1
0.5
0
Epinephrine
Glucagon
Figure 1—Sex differences in blood glucose thresholds.
1996
Autonom Sx Neuroglycop Sx
men; ^ g , women.
269