hyperglycaemia: disparity between diabetes clinic and home blood glucose concentrations

Objectives-To identify patients with discrepantly high clinic blood glucose concentrations compared with self reported values and to assess whether such patients have errors in selfmonitoring technique. To determine whether, in patients with good technique, the discrepancy is a transient phenomenon related to clinic attendance. Design-Prospective study of diabetes clinic patients recruited over six months. Setting-Outpatient diabetes clinic of a teaching hospital. Subjects-34 consecutive patients with noninsulin dependent diabetes who had had at least two consecutive clinic blood glucose concentrations more than 5 mmolll higher than the mean self reported concentration. Main outcome measures-Assessment ofmonitoring technique; presence of cognitive or physical impairment; serum fructosamine concentration; home and clinic blood glucose concentrations. Results-i5 of 34 patients had errors in monitoring technique, 12 of whom had cognitive or physical impairment. In the remaining 19, the mean (SD) blood glucose concentrations of capillary and venous samples taken at home (10.2 (0 6) and 12-2 (1.1) mmol/l respectively) were significantly lower than in those taken at the clinic (16.8 (1.6) mmolll, p < 0.0002). The fructosamine concentration was St Vincent's Hospital, significantly higher in patients with monitoring StyVianent'S Hsa, errors than those without (2.4 (0.4) v 18 (0-4) Asydny,NSl 210 mmolIl, p <0.0001). Lesley V Campbell, director Conclusions-"White coat" hyperglycaemia was Sheena M Ashwell, clintical detected in about half the patients but errors nzurse consultant in technique accounted for the rest of the discrepancies. Patients' ability should be assessed before Garvan Institute ofMedical teaching self monitoring and the technique checked Research, St Vincent's regularly. Hospital, Sydney, Australia Mark Borkman, researchi fellow Introduction DonaldJChisholm, professor Dofnad JChisholm,p s Self monitoring of blood glucose concentration is commonly used to assess glycaemic control in diabetes, Correspondence to: and when done properly it is accepted as a reliable and Dr Campbell. accurate indicator. ' A survey of our diabetic outpatient clinic showed that 97% of insulin dependent and BA1J1992;305:1194-6 67% of non-insulin dependent diabetic subjects were TABLE I-Clinical charactenrstics and glycaeniic nmeasuires of the error anid non-error groups. Concurrent data frno 412 non-insulin dependent diabetic patients attending the clinic over the samie six nmotnths. Values are mzeans with SD inl parentheses All non-insulin Non-error dependent diabetic All sub jectst Error group group patients at clinic (n = 34) (n = 15) (n = 19) (n = 4 121) Age (years) 68 (8-8) 68 (10-8) 68 (7 1) 65 (10-1) Duration of diabetes (years) 8 (9) 8 (7) 9 (5) Blood glucose (mmol/l) Selfmonitoring 9-1 (1-8) 10-1 (2-0) 8-4 (1-1)" Clinic 17-7 (2-5) 18-9 (2-9) 16-8 (1-6)* 11-3 (4-1) Difference between clinic and self monitoring 8-6 (1-8) 8-8 (2-1) 8-4 (1-5) Clinic serum fructosaminet (mmolUl) 2-0 (0-6) 2-4 (0-4) 1-8 (0-4)** 1-8 (0-4) *p< 0 01, **p = 0 001 Compared with error group. tFructosamine reference range < 1 8 mmolUl. tThe 34 subjects were drawn from the 412 clinic patients. monitoring their own glucose concentrations.2 In our experience elderly patients with diabetes can be taught monitoring; routine checking of technique within two weeks has shown performance comparable with that in younger patients. In the outpatient clinic doctors use the patient's clinic blood glucose concentration and the self recorded log book to assess recent glycaemic control. It is not uncommon to find that the patient's clinic blood glucose concentration is high compared with the self reported levels. Patients often ascribe this to the stresses of attending clinic such as transport, parking, erratic eating, waiting, and fear of the clinic procedures (or staff). This is analogous to the phenomenon of "white coat hypertension,"3 in which blood pressure is higher in the clinic than at home. In some patients the glucose discrepancy is large enough to warrant a change of treatment if the clinic test were the true reflection of glycaemic control. This presents the clinician with a management dilemma. A large discrepancy which is present at consecutive clinic visits suggests either inaccurate self monitoring or transient hyperglycaemia at clinic which is unrepresentative of usual glycaemic control. Although indices of long term control are also measured, such as glycated haemoglobin or serum fructosamine concentration (a measure of the glycation of albumin), the results are not generally available while the patient is at the clinic. Uncertainty about a patient's current glycaemic control can lead doctors to adjust treatment inappropriately. Some clarification of the likely causes of the discrepancy would be beneficial in managing such patients. In this study we set out, firstly, to identify those patients with a repeated and large glycaemic discrepancy; secondly, to determine whether such discrepancy was related to errors in self monitoring technique; and, thirdly, if there was no technique error to examine if the discrepancy was due to transient hyperglycaemia related to clinic attendance. Subjects and methods