|
Before doing Laboratory Investigations in Diabetes Mellitus ask yourself for what purpose
are you doing?
(1) Is it for Diagnosis?
Urine Glucose is not enough. Blood glucose should be done atleast twice and it should
be in the diagnostic range.
(2) To Assess control.
Glycosylated HB Vs Stat Blood Sugar. For Long term assessment Glycosylated
Haemoglobodin is useful.
(3) Diagnosis of Hypoglycemia
Random Blood Glucose at the time of symptoms is diagnostic.
(4) Diagnosis of Reactive Hypoglycemia. 6 hours extended OGTT is useful.
(5) Research purpose to study the 1st degree Relatives of Diabetics. OGTT study is done.
(6) To know whether patient is in Remission.
C Peptide estimation is useful in addition to routine tests.
(7) To detect Early Renal Involvement. Microalbuminuria is useful.
(8) To find out if patient is in ketosis. Urine ketone testing
Blood glucose estimation
Blood collection in Sodium Fluoride bulb retains the sugar value for several hours at
Room Temp. Several Days if kept in Refrigerator with 10% loss occur. Autoanalyser uses plasma for sugar estimation and the value is 15% higher than whole blood sugar. Follin and Wu's - method gives 20 mgm higher value for blood glucose because of non glucose reducing substances. Somogy Nelson's Method -Estimates True Glucose 20 mgm less than Follin Wu Method. Capillary blood glucose is 20-50 mgm higher both in post meal and fasting.
Advantage of capillary blood sugar estimation is that it is easy to perform in children when repeated blood glucose is to be estimated and when vein is not available.
Dextrometer needs small amount of capillary blood. It is not used for firs*- time diagnosis
of Diabetes.
| Plasma Glucose |
Whole Blood Glucose |
| a. |
Plasma Glucose not affected by Haematocrit |
a. Affected bv Haematocrit 10 units decrease will increase Blood sugar by 3.6 mgm. |
| b. |
Reflects Concentration of glucose in Extra-celluar fluids. |
b. Reflects Infra-vascular compartment Blood Glucose. |
| c. |
Adaptable for Auto-Analvser |
c. Not Adaptable. |
Arterial Blood Sugar is 20-50 mgm higher than venous blood sugar in normal adults. In
diabetic Arterial and Venous difference is lost meaning glucose is not utilised by tissues.
Oral Glucose Tolerance Test (OGTT)
Low Carbohydrate diet can make OGTT diabetic type. Decreased physical activity gives
diabetic type of curve with OGTT. Infection, Obesity, Carcinoma, Endocrinopathies, can impaire OGTT. Drugs like thiazides, Steroids, Aspirin, O.C.A. Nicotinic Acid and dilantin increase 2 hrs. post meal blood glucose estimation.
Brittle diabetic mellitus requires 24 hours urinary glucose quantitative estimation.
Pitfalls in management of diabetes
Often Diabetes Mellitus patients on OHA therapy comes for follow up and fasting Blood
Glucose is found raised. Before thinking that he is not well controlled and changing the dose of OHA. Ask him two questions.
1. Is it really fasting or has he taken break fast before giving blood.
2. Did he omit his last night OHA. This mistake is often done by patients. They omit the
drugs and go for tests. They think that they have taken treatment continuously for 1
month and want to see the sugar report without drugs. I always explain them most of the
OHA preparations except Chlorpropamide acts only for that day i.e. 24 hours.
Often patients manupulate the dose of OHA. If they have been prescribed BD dose they
may make it OD dose. While looking into post meal blood sugar, verify it was really 2
hours later or at shorter interval like one hour or one and half hours. This will also raise
the blood sugar. While reviewing Glycosylated Hb. if there is Anemia or Chronic renal
disease, it is bound to cause normal or low values.
3. Glycosylated Hb is not the correct choice of test during Hypoglycemia or diabetic
ketoacidosis. Acute blood glucose changes are not reflected in Glycosylated Hb values.
4. Some general practioners in a known diabetic get post glucose blood sugar value.
There is no need to give glucose once the diabetes mellitus diagnosis is made. Check
out this mistake while evaluating postmeal blood glucose values.
5. In a patient on insulin, if you are getting uncontrolled values, before changing insulin
dose check out what syringe the patient used. Insulin syringe or ordinary syringe, upto
which mark he took insulin. This will vary in U80 and U100 Syringes or in the same
syringe where U40 and U80 is marked and if the patients is taking dosage from mark
U80 actually he is taking half the dosage only.
6. Insulin injection technique has to be told to the patient. Some diabetics are in a habit of
taking insulin at the same site. This is going to make poor absorption of insulin from the
site of injection and hence uncontrolled diabetic state. Physician has to tell the patient to
change the site of injection every time so that the site is repeated every 5-7 days.
7. Once Nephropathy develops there is insulin sensitivity, hence patients are prone to
hypoglycemic episodes. If the patient is on OHA best is to start regular insulin small
doses (10 units or 5 units) and then increase.
8. With Retinopathy patients there is difficulty in seeing and filling syringe upto correct
mark. Hence they may need help from family members to inject insulin. Some women
diabetics are in the habit of fasting 3-4 days in a week. Eating less and omitting night
dose of OHA or insulin or if they take same dose of insulin or OHA they may get frequent
Hypoglycemia. Best thing is to avoid fasting or in those days she can take food items
allowed during religious fast and take reduced dose of OHA or insulin.
9. Sick day rules are to be clearly told to the IDDM patients on insulin. During sickness
patients stop insulin completely and end up in Diabetic ketoacidosis. We have to explain
that blood glucose is maintained in normal range in non-diabetic during fasting because
of Neoglucogenesis and Glycogenolysis in liver. This phenomenon is more so in
diabetics due to insulin lack and during stressful states like Sickness, blood sugar is
increased. Best thing is to take regular insulin in a small dose, say, 10 units and check
urine every 4 hourly and take small repeated doses or consult the Physician
immediately.
10. Quite often foot infection i.e. Cellulitis or infected Ulcer occurs and patient is found on
OHA uncontrolled. He should consult Physician and immediately from OHA he has to
switch over to insulin with appropriate antibiotics. Then only the lesion will heal.
11. Similarly during pregnancy in NIDDM oral agents have to be stopped and insulin
should be started.
CONCLUSION
Physician has to be alert in interpreting blood sugar results and he must give enough time
to his patients to avoid the diabetic patients getting into various management problems.
REFERENCES
1. M. Viswanathan V. Mohar & A Rama Chandran-Diagnosis of Diabetes in Practice of
Diabetes Mallitus Edited by MMS Ahuja, Vikas Publishing House 1983, Page 79-99.
|
