Laboratory parameters of the 1st order – obligatory laboratory tests.
- HbA1c level (long-term blood glucose value):
- Diagnostic marker: ≥ 6.5% [Both the German Diabetes Society and the American Diabetes Association consider glycated hemoglobin to be a relevant diagnostic marker, provided it has been determined according to an internationally standardized procedure].
- Prognostic marker: ≥ 5.6% [patients who have an HbA1c ≥ 5.6% on random testing are highly likely to develop diabetes]
- To prevent subsequent complications, an HbA1c corridor of 6.5% to 7.5% (48 to 58 mmol/mol) should be targeted, taking into account individualized treatment goals; < 6.5% only under the following conditions:
- Lowering achievable by lifestyle modification alone or.
- Lowering achievable with medications that do not carry an increased risk of significant adverse events (eg, severe hypoglycemia (low blood glucose), heart failure (heart failure), pancreatitis (inflammation of the pancreas), substantial weight gain) and that have proven benefit on clinical end points.
- Glucose (measured in blood plasma, venous).
- [Fasting glucose (fasting plasma glucose; preprandial plasma glucose; venous) [To confirm the diagnosis, a defined elevated blood glucose value must be present on at least two occasions]
- Postprandial plasma glucose (venous), 1 to 2 h postprandial [therapy target: 140-199 mg/dl; 7.8-11.0 mmol/l].
- Glucose measurement at random time point/opportunity blood glucose (“random plasma glucose”).
- [V. a. Diabetes mellitus: ≥ 200 mg/dl (11.1 mmol/l) and typical symptoms such as polydipsia/increased thirst, polyuria/diseased increased urine output, etc.].
- Daily blood glucose profile
- OGTT test [≥ 11.1 mmol/l 2 hours after oral administration of 75 g glucose]
- Urine status (rapid test for: glucose and ketone bodies); only in case of high glucose levels.
- Albumin determination in urine (albuminuria/microalbuminuria) – in high-risk patients (patients who have poorly controlled plasma glucose or hypertension).
- Electrolytes – potassium
- Renal parameters – urea, creatinine, cystatin C or creatinine clearance, if necessary.
[Diagnostic criteria for diabetes mellitus] 2nd order laboratory parameters – depending on the results of the history, physical examination, etc. – for differential diagnostic clarification.
- Autoimmune diagnostics in diabetes mellitus:
- Anti-glutamic acid decarboxylase antibody/anti-glutamic acid decarboxylase autoantibody (anti-GAD65-Ak).
- Anti-tyrosine phosphatase antibody/autoantibody to protein tyrosine phosphatase IA 2 (IA-2-Ak), an islet cell antigen (anti-IA 2).
To identify patients with autoimmune diabetes or LADA (late onset autoimmune diabetes in the adult; late manifestation of diabetes mellitus type 2); if positive, if necessary, then molecular genetic diagnostics for 35 subtypes of monogenic forms of diabetes.
- Fasting insulin
- NT-proBNP (N-terminal pro brain natriuretic peptide) – if heart failure (heart failure) is suspected or to clarify this risk.
- Lp-PLA2 (vascular inflammatory enzyme lipoprotein-associated phospholipase A2; inflammatory marker) – for risk stratification of cardiovascular disease.
Further notes
- In the early phase of type 2 diabetes mellitus, hyperglycemia (pathologically elevated glucose level) is present despite hyperinsulinemia (pathologically elevated insulin level). Only in the further course of the disease, the insulin serum level decreases.
- The fasting insulin serum level may be elevated without the fasting glucose serum level being elevated! → Then suspect insulin resistance (see HOMA index under “fasting insulin”).
- C-peptide (part of proinsulin): measuring a fasting value of C-peptide in plasma can support the decision on insulin therapy. Assessment: values < 200 pmol/l (0.6 ng/ml) clearly indicate insulin dependence, i.e., insulin-dependent diabetes mellitus.
- Notice: In extremely rare cases, the following special form may be present: LADA (latent autoimmune diabetes (with onset) in adults) – type 1 diabetes with manifestation in adulthood (> 25 years); insulin deficiency develops relatively slowly. No insulin requirement in the first 6 months, detection of GAD-Ak (glutamic acid decarboxylase; English : glutamic-acid-decarboxylase = GAD; a ß-cell-specific enzyme).
- In men: andropause diagnostics – testosterone is an important modulator of insulin sensitivity: testosterone increases insulin sensitivity!
The following laboratory parameters, which are considered independent risk factors for atherosclerosis, should be investigated.
- Cholesterol (HDL; LDL) [therapeutic goal: LDL cholesterol lowering to target < 100 mg/dl (< 2.6 mmol/l) (DDG / DGIM); fixed statin dose strategy (AkdÄ, DEGAM)]
- Homocysteine
- Lipoprotein (a)
- Apolipoprotein E – genotype 4 (ApoE4)
- Fibrinogen
- CRP
Oral glucose tolerance test (oGTT) [gold standard]
The oral glucose tolerance test – known as oGTT for short – is used for the early detection of diabetes mellitus and for the detection of preliminary stages of diabetes disease. The test checks to what extent the β-cells (B-cells) of the pancreas are still functional and to what extent they are still able to produce insulin. The test is performed in several steps:
- From three days before the start of the test, a high-carbohydrate diet must be followed.
- On the day of the examination, blood is first taken on a fasting basis. Fasting means that the patient must come to the examination without having eaten or drunk anything in the past 8 hours (fasting blood glucose level).
- Then he drinks fasting 75 g of glucose dissolved in tea or a ready preparation: 75 g of dextrose, for example, Dextro-Energen to 300 ml of water.
- The glucose serum level of the patient is measured fasting and after 2 hours.
The results clearly indicate whether the patient is healthy, reduced glucose tolerance or already has diabetes. According to the German Diabetes Society, there are the following diagnostic criteria (AWMF guideline):
Postprandial, nonpregnant (OGT- 2h value).
| Plasma, venous | Whole blood (capillary, hemolyzed) | Assessment |
| < 140 mg/dl (< 7.8 mmol/l) | < 140 mg/dl (< 7.8 mmol/l) | Normal |
| 140-199 mg/dl (7.8-11.0 mmol/l) | 140-199 mg/dl (7.8-11.0 mmol/l) | Impaired glucose tolerance (IGT). |
| ≥ 200 mg/dl (≥ 11.1 mmol/l) | ≥ 200 mg/dl (≥ 111 mmol/l) | Diabetes mellitus |
- Abnormal fasting glucose is present when the fasting value is between 100-126 mg/dl (5.6-7.0 mmol/l)
Confounding factors
- False-positive results can occur with too little carbohydrate intake on previous days or medication use such as diuretics or laxatives.
- False-negative results may occur with antihypertensives or physical activity during the test.
Important notes.
- Notice: If the two-hour value is elevated in the OGT, one-third of the insulin-producing beta cells have already failed.
- Patients with abnormal fasting glucose (impaired fasting glucose, IFG) and patients with impaired glucose tolerance (impaired glucose tolerance, IGT) are at risk for diabetes mellitus and macroangiopathy. Here, lifestyle-modifying measures are to be offered.
