A random plasma glucose method for screening for gestational diabetes.JR Maheshwari, MV Mataliya
Low renal threshold for glucose during pregnancy renders glycosuria less specific for the diagnosis of gestational diabetes. Screening for gestational diabetes was done by utilising random plasma glucose (RPG). RPG was done at the first antenatal visit. In 12,623 patients who registered for antenatal care at the N.W.M. Hospital, 1371 patients had a RPG more than 100 mg%. An oral glucose tolerance test was advised in these patients. The pick-up rate of gestational diabetes correlated with RPG level. Thirty-six cases of gestational diabetes were picked up. The pick up rate is significantly higher as compared to that which would have been detected utilising conventional screening criteria.
Keywords: Blood Glucose, analysis,Female, Glucose Tolerance Test, Human, India, Mass Screening, methods,Pregnancy, Pregnancy in Diabetics, blood,prevention &control,Prenatal Care,
Conventionally, screening of women for gestational diabetes has been based upon the presence of stigmata said to be associated with disease. However, such a testing would result in 38% of diabetics going unidentified.
An oral glucose tolerance test (OGTT) performed on all pregnant women would detect almost all diabetics, but at a prohibitive cost in terms of finance, staff and patient inconvenience. Lind and McDougall utilised random blood glucose (RBG) sampling as a screening procedure in selecting patient who were to be subjected for an OGTT. However, they utilised different cut off levels of RBG depending whether the patient had her last meal within past 2 hours or not.
We at N.W.M. Hospital, Bombay, employed random plasma glucose (RPG) sampling as a screening procedure at the first antenatal visit for selecting patients to be subjected for an OGTT. The aim of the study was to determine the cut off level of RPG at which the patient should be subjected to an OGTT. Simultaneously we also studied the number of gestational diabetics who would have been detected, if an OGTT was performed on the basis of diabetic stigmata alone.
A total of 12623 patients presented for antenatal registration at the hospital between 1st June, 1987 to 31st July, 1988. RPG value was done at the 1st visit in all patients. Known diabetics were excluded from the study. Venous blood (2 ml) was obtained by venepuncture from an antecubital vein, anticoagulated in a fluoride containing tube and plasma glucose was estimated within 3 hours of collection using an auto-analyser which utilises the specific enzyme glucose oxidase.
Out of the total, 1371 (10.9%) patients had a RPG level of more than 140 mg%. These patients were divided into 3 groups as follows:
Group I : RPG value between 101 and 120 mg%
Group II : RPG value between 121 and 140 mg%
Group III : RPG value more than 140 mg%.
Oral Glucose Tolerance Test (OGTT)
An OGTT was advised in all patients in the three groups, so as to determine the pick up rate of gestational diabetes in each group. Of the 1371 patients, 477 patients followed up for OGTT. These OGTTs were all performed between 28-34 weeks gestation. Women referred for this test were asked to attend at 08.30 hours having fasted overnight for at least 12 hours. After they had been sitting quitely at rest for 30 minutes, a venous blood sample was obtained from an antecubital vein, after which 75 gm glucose drink was given. A second sample was obtained at 120 minutes after the drink.
Criteria for abnormal OGTT
The criteria for abnormality recommended by the WHO were used. If 2 hour venous plasma level was more than 198 mg%, the test was diagnostic of diabetes. When the value was between 144-198 mg%, the diagnosis of gestational diabetes was made.
As seen in [Table - 1]1371 (10.9%) had RPG more than 1,00 mg%. One thousand and eighty one (8.6%) patients had RPG values between 101-120 mg%, 257 (2.0%) between 121-140 mg% and 33 (0.3%) more than 140, mg%.
As seen in[Table - 2], 477 patients presented to OGTT. Of these 36 patients i.e. 7.55% had an abnormal OGTT. In Group 1 (101-120 mg%)-13/328 (3.96%), in group 11 (121-140 mg%). - 15/129 (11. 63%) and in Group III (> 140 mg% ) -8/20 (40%) patients yielded an abnormal OGTT.
As seen in[Table - 3], of 477 patients who had an OGTT done, only 277 had conventional indications for screening of diabetes, 21/277 (7.58%) yielded an abnormal OGTT.
The objective in screening for diabetes during pregnancy is to detect all women with an abnormal OGTT because of the known adverse effect of this condition on the fetus. However, it would be necessary to perform an OGTT on all pregnant women at an appropriate period of gestation to do this with certainty. This is impractical, as the majority of patients would be subjected to an expensive, inconvenient and time consuming investigation.
Various methods of screening have been suggested so as to reduce the number of OGTT required. O'Sullivan et al have suggested routine 1 hour blood glucose level following oral ingestion of 50 gm of glucose, in all patients and an OGTT performed on those patients with levels exceeding 130 mg%. On the other hand, this screening test is inconvenient for staff and patients in a busy clinic as it involves timed blood sampling in all patients and prolonged patient stay in the clinic. Screening by RBG and RPG sampling at 28 week has been advocated by Lind and McDougall and by Hatem and Dennis respectively. Lind and McDougall found the range of RBG value, at all time points so narrow that they divided them into those obtained within 2 hours of the last meal and those less than 2 hours after the meal. The cut off points were 118 mg% and 104 mg% respectively. This screening programme also cannot be applied in Indian hospitals as most of the patients are unable to recall the time of last meal accurately. In the current study, RPG value more than 100 mg% (irrespective of last meal) was utilised as a basis for OGTT. The incidence of abnormal OGTT increased from 3.96%, when RPG ranged from 101-120, to 40% when RPG exceeded 140 mg%, though 3.96% is a low pick up rate, it still accounts for 13/36 (36.11%) of gestational diabetics, that were ultimately detected. Thus, it is essential to advise an OGTT even in these patients whose RPG ranges between 101 and 120 mg%.
Utilising conventional screening criteria of stigmata of diabetes, yielded 11 abnormal GTT in 150 tests. In the current study 277/477 had conventional screening criteria. This detected 21 (7.58%) gestational diabetics in 277 tests. However, this procedure would fail to detect a significant number i.e. 15 (41.66%) of the gestational diabetes which corroborates with the findings of O'Sullivan et al.
In conclusion, utilising conventional screening criteria is an inadequate procedure. A random plasma glucose level more than 100 mg% at the first antenatal visit as a basis for subsequent OGTT serves as a simple, efficient, convenient screening procedure for detecting gestational diabetes.
We thank the Dean, N.W.M. Hospital, for allowing us to use the hospital data. We also thank Honorary Medical Staff and Pathology Department for their help and co-operation in conducting this study.
[Table - 1], [Table - 2], [Table - 3]