Diabetes Diagnosis - Signs and symptoms, Diagnostic approach,Diagnostic criteria

When the glucose concentration in the blood is high (above the "renal threshold"), reabsorption of glucose in the proximal renal tubuli is incomplete, and part of the glucose remains in the urine (glycosuria). This increases the osmotic pressure of urine and thus inhibits the reabsorption of water, resulting in an increased urine producton (polyuria) and an increased fluid loss from the blood. The lost blood volume will be replaced from water held in body cells, causing dehydration and increase thirst. Prolonged high blood glucose causes changes in the shape of the lens in the eye, leading to vision changes. Blurred vision is a common complaint leading to a diagnosis of type 1; it should always be suspected in such cases.

Patients (usually with type 1 diabetes) may also present with diabetic ketoacidosis (DKA), an extreme state of dysregulation characterized by the smell of acetone on the patient's breath, Kussmaul breathing (a rapid, deep breathing), polyuria, nausea, vomiting and abdominal pain, and any of many altered state of consciousness or arousal (e.g., hostility and mania or, equally, confusion and lethargy). In severe DKA, coma (unconsciousness) may follow, progressing to death if untreated. In any form, DKA is a medical emergency and requires expert attention.

A rarer but equally severe presentation is hyperosmolar nonketotic state, which is more common in type 2 diabetes, and is mainly the result of dehydration due to the polyuria. Often, the patient has been drinking extreme amounts of sugar-containing drinks, leading to a vicious circle in regard to water loss.

The diagnosis of type 1 diabetes and many cases of type 2 is usually prompted by recent-onset symptoms of excessive urination (polyuria) and excessive thirst (polydipsia), often accompanied by weight loss. These symptoms typically worsen over days to weeks; about 25% of people with new type 1 diabetes have developed a degree of diabetic ketoacidosis by the time the diabetes is recognized. The diagnosis of other types of diabetes is usually made in many other ways. The most common are (1) health screening, (2) detection of hyperglycemia when a doctor is investigating a complication of longstanding, unrecognized diabetes, and (3) new signs and symptoms attributable to the diabetes.

   1. Diabetes screening is recommended for many types of people at various stages of life or with several different risk factors. The screening test varies according to circumstances and local policy and may be a random glucose, a fasting glucose and insulin, a glucose two hours after 75 g of glucose, or a formal glucose tolerance test. Many healthcare providers recommend universal screening for adults at age 40 or 50, and sometimes occasionally thereafter. Earlier screening is recommended for those with risk factors such as obesity, family history of diabetes, high-risk ethnicity (Hispanic/Latin American, American Indian, African American, Pacific Island, and South Asian ancestry).
   2. Many medical conditions are associated with a higher risk of various types of diabetes and warrant screening. A partial list includes: high blood pressure, elevated cholesterol levels, coronary artery disease, past gestational diabetes, polycystic ovary syndrome, chronic pancreatitis, fatty liver, hemochromatosis, cystic fibrosis, several mitochondrial neuropathies and myopathies, myotonic dystrophy, Friedreich's ataxia, some of the inherited forms of neonatal hyperinsulinism, and many others. Risk of diabetes is higher with chronic use of several medications, including high-dose glucocorticoids, some chemotherapy agents (especially L-asparaginase), and some of the antipsychotics and mood stabilizers (especially phenothiazines and some atypical antipsychotics).
   3. Diabetes is often detected when a person suffers a problem frequently caused by diabetes, such as a heart attack, stroke, neuropathy, poor wound healing or a foot ulcer, certain eye problems, certain fungal infections, or delivering a baby with macrosomia or hypoglycemia.

Diabetes mellitus is characterized by recurrent or persistent hyperglycemia, and is diagnosed by demonstrating any one of the following:[1]

    * fasting plasma glucose level at or above 126 mg/dL or 7.0 mmol/l.
    * plasma glucose at or above 200 mg/dL or 11.1 mmol/l two hours after a 75 g oral glucose load in a glucose tolerance test.
    * random plasma glucose at or above 200 mg/dL or 11.1 mmol/l.

A positive result should be confirmed by any of the above-listed methods on a different day, unless there is no doubt as to the presence of significantly-elevated glucose levels. Most physicians prefer measuring a fasting glucose level because of the ease of measurement and time commitment of formal glucose tolerance testing, which can take two hours to complete. By definition, two fasting glucose measurements above 126 mg/dL or 7.0 mmol/l is considered diagnostic for diabetes mellitus.

Patients with fasting sugars between 6.1 and 7.0 mmol/l (110 and 125 mg/dL) are considered to have "impaired fasting glucose" and patients with plasma glucose at or above 140mg/dL or 7.8 mmol/l two hours after a 75 g oral glucose load are considered to have "impaired glucose tolerance". "Prediabetes" is either impaired fasting glucose or impaired glucose tolerance; the latter in particular is a major risk factor for progression to full-blown diabetes mellitus as well as cardiovascular disease. While not used for diagnosis, an elevated level of glucose bound to hemoglobin (termed glycosylated hemoglobin or HbA1c) of 6.0% or higher (2003 revised U.S. standard) is considered abnormal by most labs; HbA1c is primarily a treatment-tracking test reflecting average blood glucose levels over the preceding 90 days (approximately). However, some physicians may order this test at the time of diagnosis to track changes over time. The current recommended goal for HbA1c in patients with diabetes is <7.0%, as defined as "good glycemic control", although some guidelines are stricter (<6.5%). People with diabetes that have HbA1c levels within this goal have a significantly lower incidence of complications from diabetes, including retinopathy and diabetic nephropathy.