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[IP] SMBG Quality Specifications (LONG)
Good morning all --
I've receive a copy of a paper just published in Clinical Chemistry about
blood glucose monitoring. The full citation is
Svein Skeie, Geir Thue, and Sverre Sandberg. Patient-derived Quality
Specifications for Instruments Used in Self-Monitoring of Blood Glucose.
Clinical Chemistry 47:1, pages 67-73 (2001).
The work is the product of NOKLUS, the Norwegian Center for External Quality
Improvement of Primary Care Laboratories, Division of General Practice,
Ulriksdal 8c, University of Bergen, N-5009, Bergen, Norway. Correspondence
to the author at: Department of Medicine, Rogaland Central Hospital, PO Box
8100, 4068 Stavanger, Norway. Email: mailto:email @ redacted.
I'm copying the abstract and part of one paragraph in the discussion, and
adding a personal comment at the end.
Instruments for self-monitoring of glucose (SMBG) are increasingly used by
diabetic patients. Information is limited on how patients use and interpret
SMBG results, and no quality specifications for such instruments are based
on the opinions of patients.
Type 1 diabetic patients (n = 201) filled in a questionnaire eliciting daily
limits for blood glucose (BG) and changes of BG considered significant at
different glucose concentrations. From these responses, patient-derived
quality specifications were calculated in different clinical situations with
low, intermediate, and high BG concentrations.
Mean age of the patients was 31.8 years, mean diabetes duration was 14.7
years, and mean SMBG durations was 10.0 years with a mean frequency of 11.2
measurements/week. The threshold for hypoglycemic symptoms was 3.0 mmol/L
(54 mg/dL), and the mean daily target window was 4.3-10.4 mmol/L (77-187
mg/dL). The mean absolute BG changes producing actions from the patients
ranged from 1.1 mmol/L (20 mg/dL) to 3.6 mmol/L (65 mg/dL). The analytical
quality specifications for imprecision depended on the clinical situation.
Excluding the hypoglycemic situation, the analytical CV needed to fulfill
the expectations of 75% of the patients was 6.4-9.7%. The analytical
quality specifications for CV at hypoglycemic concentrations was 3.1%.
Instruments for self-measurements of glucose with an imprecision (CV) of </=
5% and bias </= 5% meet the expectations of >75% of patients in clinical
situations other than hypoglycemia.
>From the discussion:
Patients expect meters to provide high analytical quality over the entire
range of BG measurements; these expectations are difficult to meet with
current BG monitors. Quality specifications set by the patients should be
challenged with studies testing current BG meters in the hands of the users.
In line with the ADA recommendations for the future, we also recommend that
current meters should have an imprecision of 5% or less to meet patient
expectations. Education in SMBG should focus on the limitations of portable
BG meters and errors involved in the interpretation of BG results. However,
education should also focus on the therapeutic actions to be taken in a
variety of clinical situations, and not only when the measured BG is in the
Coefficient of Variation (CV) is a very problematic statistic to use in
this, or any other laboratory situation. The assumptions of the
distribution of the data are rather strict, and most laboratory methods
produce data with a complex distribution that is not consistent with the
assumptions required for a meaningful CV. On the other hand, this work is
the first to objectively study SMBG from the patient perspective, and as
such is to be applauded, but I would have preferred to see a more rigorous
statistical analysis of the data.
The fact that all the patients were type 1 diabetics may bias these data in
that there may be a qualitative difference in the way type 1 and type 2
diabetics approach SMBG. It would be well to repeat the study targeting
SMBG in type 2 diabetics. However, some of the conclusion regarding patient
education vis a vis the precision level of portable meters is well taken
regardless of being type 1 or type 2.
I'm not too optimistic that other recommendations regarding improving the
precision will be forthcoming too soon. The current standards under the
Clinical Laboratory Improvement Amendments of 1988 (CLIA 88) are under
attack by the American Medical Association as being too stringent, and there
are concerted lobbying efforts to relax the standards, not strengthen them,
particularly with respect to laboratory testing done in physicians' offices
and home testing.
The bottom line is to be aware that there is an inherent imprecision in SMBG
meters, as well as a probably bias (systematic error) in each of them as
well. If you suspect that *YOUR* meter is not performing up to your
specifications, then get in touch with the manufacturer.
mailto:email @ redacted OR
mailto:email @ redacted
The opinions expressed are my own and do not necessarily represent those of
my wife who runs this house and makes more important decisions than I do.
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