Dr. BASIM AUDIB
Professor of MedicineF.I.C.M.S, F.R.C.P (Edenbera)
SCE Diabetes and Endocrine (London)
Consultant of Medicine
Investigations
Urine glucoseTesting the urine for glucose with dipsticks is a common screening procedure for detecting diabetes. If possible, the test should be performed on urine passed 1–2 hours after a meal to maximize sensitivity.
Glycosuria always warrants further assessment by blood testing. The greatest disadvantage of urine glucose measurement is the individual variation in renal threshold for glucose.
The most frequent cause of glycosuria is a low renal threshold, which is common during pregnancy and in young people; the resulting ‘renal glycosuria’ is a benign condition unrelated to diabetes. Another disadvantage is that some drugs (such as βlactam antibiotics, levodopa and salicylates) may interfere with urine glucose tests
Blood glucose
Laboratory glucose testing in blood relies on an enzymatic reaction (glucose oxidase) and is cheap, usually automated and highly reliable. However, blood glucose levels depend on whether the patient has eaten recently, so it is important to consider the circumstances in which the blood sample was taken.Blood glucose can also be measured with testing sticks that are read with a portable electronic meter. These are used for capillary (finger prick) testing to monitor diabetes treatment
Many countries now offer self monitoring only to people with type 2 diabetes taking sulphonylurea or insulin therapy because of the risk of hypoglycaemia
To make the diagnosis of diabetes, the blood glucose concentration should be estimated using an accurate laboratory method rather than a portable technique.
Interstitial glucose
A relatively new approach to measuring glucose levels in diabetes is through the use of interstitial continuous glucose monitoring (CGM). CGM systems use a tiny sensor inserted under the skin to check glucose levels in interstitial fluid. The sensor can stay in place for up to 2 weeks before being replaced and provides real time measurements of glucose levels every 1 or 5 minutesUrine and blood ketones
Acetoacetate can be identified in urine by the nitroprusside reaction, using either tablets or dipsticks. Ketonuria may be found in normal people who:-Fasting
-Exercising strenously for long period
-Repeated vomiting
-Diet with high fat and low carbohydrate
Ketonuria is therefore not pathognomonic of diabetes but, if it is associated with glycosuria, the diagnosis of diabetes is highly likely
Glycated haemoglobin (HbA1c)
Sometimes also reffered as Hb1c. It is a form of Hb that is measured to identify the three month average plasma glucose concentration ( life span of RBCs, 120 days).
HbA1c is an important indicator for long term glucose control and has recently been recommended for use in the diagnosis of diabetes mellitus.
In DM, higher amounts of HbA1c, indicating poorer control of blood glucose levels, have been associated with cardiovascular disease, nephropathy, neuropathy, and retinopathy.
HbA1c :Interpretation of results
Normal below 5.7%Prediabetics 5.7 to 6.4%
Diabetics 6.5% or greater
Conditions falsely increase HbA1c
Chronic Excessive alcohol intakeHypertriglyceridemia
Conditions falsely decrease HbA1c
Acute or chronic blood lossSickle cell disease
Thalassemia
Chronic kidney disease
Various assay methods are used to measure HbA1c, but most laboratories have been reporting HbA1c values (as %) with the reference range that was used in the Diabetes Control and Complications Trial (DCCT) aligned.
The International Federation of Clinical Chemistry (IFCC) has developed a standard method; values are reported in mmol/mol
HbA1c = 6.5%
48 mmol/mol
Islet autoantibodies
Type 1 diabetes is a characterized by autoimmune destruction of the pancreatic β cells, it can be useful in the differential diagnosis of diabetes to establish evidence of such an autoimmune processIf autoantibodies are present at high titer, this can be supportive of a diagnosis of type 1 diabetes. The antibodies that are measured are:
1- Islet cell antibodies
2- Glutamic acid decarboxylase antibodies (GAD)
3- Insulin antibodies
4- Protein tyrosine phosphatase-related proteins
5- Zinc transporter (ZnT8)
Urine protein
Standard urine dipstick testing for albumin detects urinary albumin at concentrations above 300 mg/L, but smaller amounts (microalbuminuria) can only be measured using specific albumin dipsticksMicroalbuminuria or proteinuria, in the absence of urinary tract infection, is an important indicator of diabetic nephropathy and/or increased risk of macrovascular disease