CHAPTER 4 — TESTING AND DIAGNOSIS Type 2 Diabetes and insulin resistance can be tracked and understood through a small number of key blood tests. This chapter explains the most important tests, what they measure, and how they fit together so results become meaningful rather than confusing. WHY TESTING MATTERS Symptoms alone are not reliable. Some people feel unwell long before blood tests are clearly abnormal. Others feel almost normal while silent damage is already happening. Regular testing allows:
- Early detection of insulin resistance and prediabetes
- Confirmation of a diagnosis of Type 2 Diabetes
- Assessment of how well current treatment and lifestyle changes are working
- Identification of complications at an early stage
THE MAIN BLOOD SUGAR TESTS 1. Fasting plasma glucose This test measures blood sugar after not eating or drinking calories for at least 8 hours. Typical interpretation:
- Below 100 mg per dL (below 5.6 mmol per L): usually considered normal
- 100 to 125 mg per dL (5.6 to 6.9 mmol per L): often called impaired fasting glucose or prediabetes
- 126 mg per dL (7.0 mmol per L) or higher on two separate occasions: usually consistent with diabetes
2. A1C, also called HbA1c or glycated hemoglobin This test estimates the average blood glucose over the past 2 to 3 months by measuring how much sugar is attached to red blood cells. Typical interpretation:
- Below 5.7 percent: usually considered normal
- 5.7 to 6.4 percent: often classified as prediabetes
- 6.5 percent or higher on two separate tests: usually consistent with diabetes
A1C is helpful because it smooths out daily ups and downs and provides a long term view. However, certain conditions that affect red blood cells can make A1C less accurate, such as some forms of anemia or kidney disease. 3. Random plasma glucose This is a blood sugar test taken at any time of the day without regard to the last meal. If a person has typical symptoms of high blood sugar, such as increased urination, thirst, and unexplained weight loss, a random glucose of 200 mg per dL (11.1 mmol per L) or higher may support a diagnosis of diabetes and is usually followed by confirmation with other tests. 4. Oral glucose tolerance test or post meal testing In a formal oral glucose tolerance test, a person drinks a measured glucose solution and the blood sugar is tested 2 hours later. Typical interpretation for the 2 hour value:
- Below 140 mg per dL (below 7.8 mmol per L): usually considered normal
- 140 to 199 mg per dL (7.8 to 11.0 mmol per L): impaired glucose tolerance or prediabetes
- 200 mg per dL (11.1 mmol per L) or higher: usually consistent with diabetes
In everyday life, some people use post meal testing with a normal meal instead of a formal glucose drink. The principle is similar: very high glucose readings one or two hours after eating suggest reduced tolerance to carbohydrates. CONTINUOUS GLUCOSE MONITORING A continuous glucose monitor, often called a CGM, uses a small sensor under the skin to measure glucose in the tissue fluid every few minutes. Benefits include:
- Showing how specific foods affect glucose
- Revealing night time highs and lows
- Highlighting rapid spikes after meals
- Helping to adjust meal timing, composition, and medication under professional guidance
CGM readings are usually displayed as graphs and time in range percentages rather than single numbers. Time in range often becomes a practical goal alongside A1C. INSULIN AND HOMA IR Where available, fasting insulin can be measured together with fasting glucose. These two numbers can be combined into an index such as HOMA IR to estimate how resistant the body is to insulin. In general:
- Higher fasting insulin with normal glucose suggests early insulin resistance
- Falling insulin with rising glucose can indicate beta cell fatigue
These tests are not always done in routine practice but are very helpful for understanding the full picture. RELATED METABOLIC MARKERS Type 2 Diabetes does not occur in isolation. Several other tests provide useful context:
- Lipid profile:
- Triglycerides are often elevated in insulin resistance
- HDL cholesterol, the so called good cholesterol, may be low
- Liver enzymes:
- Raised liver enzymes can suggest fatty liver, which is strongly linked to insulin resistance
- Kidney function:
- Creatinine, estimated glomerular filtration rate, and urine albumin can indicate how well the kidneys are coping
- Blood pressure:
- High blood pressure and diabetes commonly appear together
- Waist measurement:
- Central waist size is a simple but powerful indicator of visceral fat
LOOKING AT PATTERNS RATHER THAN SINGLE NUMBERS No single reading tells the full story. Patterns over time are more important:
- Is fasting glucose slowly creeping upward each year
- Has A1C moved from 5.8 to 6.3 to 6.9 over several tests
- Are triglycerides rising while HDL is falling
- Do post meal readings show very high peaks
A stable or improving pattern suggests current strategies are helping. A worsening pattern is a clear signal that changes are needed. HOW OFTEN TO TEST The ideal frequency of testing depends on the stage of the condition and the plan agreed with a health professional, but general principles are:
- People at risk or with prediabetes often repeat key tests every 6 to 12 months
- People with established Type 2 Diabetes may test every 3 to 6 months, or more frequently if medication is being adjusted
- Home glucose monitoring or a CGM may be used more often when learning how the body responds to food and activity
KEY POINTS SUMMARISED
- Fasting glucose, A1C, and post meal tests form the core of diagnosis and monitoring.
- Additional markers such as triglycerides, HDL, liver enzymes, and kidney function provide important context.
- Continuous glucose monitoring offers a detailed picture of daily patterns.
- Patterns over time are more meaningful than isolated readings.
- Early testing and regular follow up help detect problems sooner and track the effect of lifestyle changes and treatments.
Later chapters will build on this knowledge and describe how specific food choices, movement, sleep, and supplements can shift these test results in a healthier direction over time.