Diagnostics of carbohydrate metabolism disorders

Clinical manifestations of acute glycemic disorders

The primary reason for evaluating carbohydrate metabolism is most often a characteristic clinical presentation. Symptoms are generally divided into two large groups according to their mechanism of onset.

Hyperglycemia symptom complex includes osmotic and catabolic manifestations:

• Severe thirst and polyuria (urine becomes sticky).
• Progressive weight loss.
• General weakness and pronounced lethargy.

Hypoglycemia symptom complex combines autonomic and neuroglycopenic signs:

• External changes: sudden pallor of the skin, cyanosis, increased sweating, and hypothermia.
• Neurological disorders: development of tremor and seizures.
• CNS and behavioral changes: drowsiness, weakness, inadequate behavior, unmotivated crying.

Laboratory diagnostic criteria

The basis for establishing a diagnosis is the determination of glucose levels on an empty stomach and 2 hours after a carbohydrate load.

Important rule: reference values strictly depend on the type of blood tested. Standard diagnostic criteria are calculated for venous plasma. If whole capillary blood is used, the upper limit of the fasting normal range will be lower (less than 5.6 mmol/L).

Criteria for venous plasma:

• Normal: fasting from 3.5 to <6.1 mmol/L; 2 hours post-load — <7.8 mmol/L.
• Impaired fasting glucose (IFG): isolated elevation of fasting glucose from 6.1 to <7.0 mmol/L.
• Impaired glucose tolerance (IGT): fasting <7.0 mmol/L, and 2 hours post-load — from 7.8 to <11.1 mmol/L.
• Diabetes mellitus (DM): fasting $\ge$7.0 mmol/L; 2 hours post-load — $\ge$11.1 mmol/L. Overt diabetes mellitus is diagnosed unconditionally if glucose exceeds 11.0 mmol/L on any random measurement.

Oral glucose tolerance test (OGTT)

If a patient exhibits borderline glycemia values, a confirmatory study is necessary — an oral glucose tolerance test with a standard load.

Testing rules:

1. The patient is given a dextrose (glucose) solution. The dose is calculated individually: 1.75 g of dry substance per 1 kg of body weight.
2. The maximum total dose of the carbohydrate load must not exceed 75 g.
3. Two control points are evaluated: baseline level (fasting) and stimulated level (exactly 2 hours after dextrose administration).

Action algorithm for detected hyperglycemia

Upon initial detection of elevated fasting blood sugar, the first mandatory step is a repeated emergency test (cito!) to confirm the result. Subsequent routing depends on the obtained figures:

1. Normoglycemia (result not confirmed): preanalytical errors (blood collection defects) or failure to follow preparation rules (not fasting) are likely. Outpatient monitoring, repeat testing following the rules, and OGTT if necessary are indicated.
2. Moderate hyperglycemia (6.1–7.0 mmol/L): suspected prediabetes (IFG). Planned or urgent hospitalization for in-depth examination is indicated.
3. Pronounced hyperglycemia (> 7.0 mmol/L fasting or > 11.0 mmol/L postprandial): high suspicion of overt DM. If accompanied by clinical symptoms, urgent hospitalization in a specialized inpatient facility is required.

In asymptomatic cases with borderline values (up to 7.0 fasting and up to 11.0 postprandial), a planned examination is indicated.

Action algorithm for incidentally detected glucosuria

The initial finding may be the presence of glucose in a single urine portion. The main task is to differentiate true diabetes mellitus from renal glucosuria or sample collection defects.

• First step: emergency blood sugar determination (cito!).
• Scenario 1 (Normoglycemia): the cause may be a urine collection defect or idiopathic renal glucosuria (decreased renal threshold for glucose). Tactics: outpatient examination or planned hospitalization. Repeat urinalysis, fasting glucose monitoring, and OGTT are prescribed.
• Scenario 2 (Hyperglycemia): high risk of diabetes mellitus manifestation. Urgent hospitalization is required.

Class and exam questions

What else to study on this topic

• Pathogenesis of osmotic and catabolic symptoms of hyperglycemia
• Mechanisms of neuroglycopenia development during blood sugar reduction
• Idiopathic (renal) glucosuria: causes of the lowered renal threshold
• Differential diagnosis of types of diabetes mellitus in children
• Preanalytical errors in blood glucose collection

Other topics in the section «Chapter 11. Endocrine Diseases in Children»

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.