Page 843 - Textbook of Pathology, 6th Edition

827

Figure 27.27 The glucose tolerance test, showing blood glucose curves (venous blood glucose) and glucosuria after 75 gm of oral glucose.

sensitive and glucose specific test is dipstick method based Besides uncontrolled diabetes, ketonuria may appear in
on enzyme-coated paper strip which turns purple when individuals with prolonged vomitings, fasting state or
dipped in urine containing glucose. exercising for long periods.
The main disadvantage of relying on urinary glucose test
alone is the individual variation in renal threshold. Thus, a II. SINGLE BLOOD SUGAR ESTIMATION. For diag-
nosis of diabetes, blood sugar determinations are absolutely
diabetic patient may have a negative urinary glucose test necessary. Folin-Wu method of measurement of all reducing CHAPTER 27
and a nondiabetic individual with low renal threshold may substances in the blood including glucose is now obsolete.
have a positive urine test.
Besides diabetes mellitus, glucosuria may also occur in Currently used are O-toluidine, Somogyi-Nelson and glucose
certain other conditions such as: renal glycosuria, alimentary oxidase methods. Whole blood or plasma may be used but
(lag storage) glucosuria, many metabolic disorders, whole blood values are 15% lower than plasma values.
A grossly elevated single determination of plasma
starvation and intracranial lesions (e.g. cerebral tumour, glucose may be sufficient to make the diagnosis of diabetes.
haemorrhage and head injury). However, two of these
conditions—renal glucosuria and alimentary glucosuria, A fasting plasma glucose value above 126 mg/dl (>7 mmol/L) is
certainly indicative of diabetes. In other cases, oral GTT is
require further elaboration here. performed.
Renal glucosuria (Fig. 27.27,B): After diabetes, the next The Endocrine System
most common cause of glucosuria is the reduced renal III. SCREENING BY FASTING GLUCOSE TEST. Fasting
threshold for glucose. In such cases although the blood plasma glucose determnitation is a screening test for DM
glucose level is below 180 mg/dl (i.e. below normal renal type 2. It is recommended that all individuals above 45 years
threshold for glucose) but glucose still appears regularly and of age must undergo screening fasting glucose test every
consistently in the urine due to lowered renal threshold. 3-years, and relatively earlier if the person is overweight or
Renal glucosuria is a benign condition unrelated to at risk because of the following reasons:
diabetes and runs in families and may occur temporarily in i) Many of the cases meeting the current criteria of DM are
pregnancy without symptoms of diabetes. asymptomatic and donot know that they have the disorder.
Alimentary (lag storage) glucosuria (Fig. 27.27,C): A rapid ii) Studies have shown that type 2 DM may be present for
and transitory rise in blood glucose level above the normal about 10 years before symptomatic disease appears.
renal threshold may occur in some individuals after a meal. iii) About half the cases of type 2 DM have some diabetes-
During this period, glucosuria is present. This type of related comlication at the time of diagnosis.
response to meal is called ‘lag storage curve’ or more iv) The course of disease is favourably altered with treat-
appropriately ‘alimentary glucosuria’. A characteristic ment.
feature is that unusually high blood glucose level returns to
normal 2 hours after meal. IV. ORAL GLUCOSE TOLERANCE TEST. Oral GTT is
2. Ketonuria. Tests for ketone bodies in the urine are performed principally for patients with borderline fasting
required for assessing the severity of diabetes and not for plasma glucose value (i.e. between 100-140 mg/dl). The
diagnosis of diabetes. However, if both glucosuria and patient who is scheduled for oral GTT is instructed to eat a
ketonuria are present, diagnosis of diabetes is almost certain. high carbohydrate diet for at least 3 days prior to the test
Rothera’s test (nitroprusside reaction) and strip test are and come after an overnight fast on the day of the test (for at
conveniently performed for detection of ketonuria. least 8 hours). A fasting blood sugar sample is first drawn.