Diabetes mellitus: clinical presentation and diagnostics

Main Clinical Manifestations

The symptoms of the disease largely depend on the specific type of diabetes, but there is a common classical triad of complaints typical of carbohydrate metabolism disorders:

• Thirst and dry mouth (polydipsia).
• Abundant urination (polyuria). The mechanism of polyuria development is associated with exceeding the so-called "renal threshold". When blood sugar rises above 8.8 mmol/L, incomplete reabsorption occurs in the renal tubules. Glucose enters the urine, where it acts as a powerful osmotic diuretic, increasing the total volume of excreted fluid.
• Weight loss (emaciation). Paradoxically, weight loss occurs against the background of a significantly increased appetite and heavy food intake.

In addition to the classical triad, patients often present with skin and infectious manifestations. Pronounced skin pruritus is characteristic, particularly localized around the external genitalia. There is also an increased susceptibility to local purulent infections, such as recurrent furunculosis.

Clinical features depending on the type

The course of the pathological process varies radically in patients with different types of the disease:

1. Type I diabetes mellitus.

Characterized by rapid development and a younger patient age group. The clinical picture is very pronounced. There is an extremely high risk of acute life-threatening conditions. The disease often debuts with the patient being urgently admitted to the hospital in a pre-comatose or comatose state, accompanied by consciousness and psychiatric disorders.

1. Type II diabetes mellitus.

Develops slowly and gradually; this process can take weeks or even months. The course is predominantly paucisymptomatic. In most cases, the disease is detected entirely by chance during routine preventive examinations or when running routine blood tests for another reason.

Laboratory diagnostics and criteria

The foundation of diagnosis is the detection of hyperglycemia. For this, basal fasting glycemia is investigated. Normally, this indicator ranges between 3.8–6.7 mmol/L. If fasting blood serum glucose is $\ge$ 6.7 mmol/L (provided it is confirmed in two different analyses), a diagnosis of diabetes is established.

For the differential diagnosis of carbohydrate metabolism disorders (detecting diabetes or prediabetes), an oral glucose tolerance test (OGTT) is used. The patient is given a load of 75 g of glucose, after which the dynamics are evaluated:

• After 1 hour, pronounced hyperglycemia is recorded.
• After 1.5–2 hours, the glucose level may decrease slightly, but does not return to normal.

Criteria for evaluating carbohydrate metabolism (fasting and 120 minutes post-load):

• Norm: fasting < 6.7 mmol/L, peak < 11.1 mmol/L, at 120 min < 7.8 mmol/L.
• Impaired tolerance (prediabetes): fasting < 7.8 mmol/L (but above normal), at 120 min in the diagnostically significant range 7.8–11.1 mmol/L.
• Diabetes mellitus: fasting > 7.8 mmol/L, peak and at 120 min > 11.1 mmol/L.

Laboratory monitoring and complication markers

A number of additional laboratory markers are used to assess the degree of compensation, predict the course, and early detect complications:

• Glycated hemoglobin ($HbA_{1c}$). An integral indicator that reliably reflects the degree of carbohydrate metabolism compensation over a preceding prolonged period. Normal is 4–6%. In severe decompensation, the level can reach 15%. The main goal of therapy is to bring this indicator as close to normal as possible to prevent complications.
• Microalbuminuria. Serves as a crucial marker of the early, preclinical stage of diabetic nephropathy development.
• Markers of metabolic disorder progression. Include elevated blood lipids and lactic acid (lactate). An extremely dangerous sign is the development of ketoacidosis, indicated by the appearance of ketone bodies (acetone) in the blood and urine.
• Assessment of insulin secretion. Can be performed by directly determining the hormone. However, in patients on insulin therapy, the exogenous drug distorts the results. In such cases, C-peptide is determined—a reliable marker for assessing specifically endogenous (own) insulin secretion.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Pathogenesis of ketoacidosis development and the appearance of acetone in the urine
• Mechanisms of diabetic nephropathy and the clinical significance of microalbuminuria
• Glycemia dynamics during OGTT: the phenomenon of a drop to hypoglycemia at 1.5 hours
• Impact of hyperlipidemia and hyperlactatemia on the course of diabetes mellitus
• Differential diagnosis of prediabetes and manifest diabetes mellitus

Other topics in the section "Endocrine System and Metabolism"

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