Understanding diabetes lab tests and numbers

Living with type 1 diabetes (T1D) means becoming very familiar with markers like blood glucose levels. But blood glucose levels are only one measure for people with T1D. There are several other tests that your healthcare team may want to know as a way of better calibrating your T1D management.

To feel better in control of your health and management, it’s helpful to know what these tests are, what they measure, why they might be requisitioned and what the results mean. They can also help to determine if you are at risk for other health challenges or diabetes-related complications.

Hemoglobin A1c (HbA1c, glycated hemoglobin test, glycohemoglobin) is best referred to as A1c. This test can be done with a fingerstick and reported within minutes but is most commonly done in a clinic like a Life Labs through a blood draw with results typically taking less than a few days.

An A1c test gives you an estimate of your average blood glucose level over the past two to three months by measuring how much glucose is attached to your red blood cells. Red blood cells survive in your body for two to three months; if your blood glucose levels have been high, more glucose sticks to your red blood cells. For people with type 1 diabetes, A1c is usually measured every three months if targets aren’t met, or every 6 months otherwise. The A1c test can also be used to help diagnose diabetes, and a person’s A1c value also can be used to determine risk of developing diabetes complications.

The goal for an individual’s A1c is less than 7% in adults and 7.5% in children. However, A1c targets should be individualized, consider age, other medical conditions, and the risk for hypoglycemia (low blood glucose). A1c level can be affected by anemia (low blood cell count from low iron), chronic kidney disease, abnormalities of the hemoglobin molecule or a recent blood transfusion.

As A1c reflects average blood glucose over the last few months, it shouldn’t be used as a measure of day-to-day management. A more common measurement of real-time blood glucose levels is Time in Range (TIR). “Time in Range” (TIR) is the percentage of time that a person spends with their blood glucose levels in a target range. The range will vary depending on the person, but general guidelines suggest starting with a range of 3.9-10.0 mmml/L. (Over time or in special circumstances, some people decide to aim for a tighter range, such as 3.5-7.8 mmol/L.)

In a single number, TIR captures a lot about how blood glucose levels might vary throughout a day or over time.

Lipids are fatty substances found in the blood. Blood lipids test measures total cholesterol, LDL-cholesterol (low-density or “bad” cholesterol), HDL-cholesterol (high-density or “good” cholesterol), and triglycerides (another form of lipids that can be harmful at high levels).

Everyone needs cholesterol in their bodies as it is an essential cellular building block.

LDL-cholesterol is considered the ‘bad cholesterol” because it builds up in the blood vessels or sticks to the walls, potentially obstructing blood flow which can lead to cardiovascular issues like heart disease or stroke. Apolipoprotein B is a major component of low-density lipoprotein (LDL).

HDL-cholesterol is considered the ‘good cholesterol’ because it helps to remove LDL from the blood.

High triglycerides can thicken arterial walls of arteries which is another risk factor of heart disease, and extremely high triglyceride levels can contribute to inflammation, making it harder to fight infection.

Blood lipids should be measured at the time of diagnosis and then yearly, or as indicated by your health care provider. If a person also has heart disease, they should be measured more often.

The recommended values for blood lipids are:

LDL cholesterol: less than <2.0mmol/L or 50% reduction from baseline
Non-HDL <2.6 mmol/L
Apolipoprotein B <0.8 g/L

If your levels are above the target range your healthcare provider may want to consider a treatment plan to bring them down into a better range.

This test can help to detect early kidney disease. Without kidney damage, very little protein is found in the urine; kidney damage from T1D (or other causes) increases albumin in the urine.

The spot test for UACR can be done at any time: the calculation compares how much albumin is in the urine to how much creatinine is in the urine. Creatinine is the waste product in urine that comes from everyday muscle use. To specifically get the UACR measurement, the laboratory divides the albumin concentration by the creatinine concentration.

Screening should occur annually in individuals (after puberty) who have had T1D for over 5 years. The target is to have an UACR of 2.0 mg/mmol or less.

Urinary ACR is a truly important screening test that is done at the time of diagnosis and then usually once a year following. Sometimes UACR can appear high without kidney damage (such as a urinary infection or menstruation), so if the UACR is elevated, the test should be repeated. At least 2 out of 3 urine samples should exhibit high levels of albumin over 3 months before the results are considered abnormal.

The blood creatinine level indicates how well the kidneys are working. If the kidneys are challenged, creatinine levels will increase in the blood.

The normal range for creatinine in the blood is 0.84 mg/dL to 1.21 mg/dL, although these values vary between sexes, by age (levels are higher in older people), and can be different depending on the lab doing the testing. Blood creatinine can also increase from dehydration, certain medications and supplements, and in those who eat lots of meat. If the blood creatinine level is high, and still high after the test is repeated, healthcare professionals will look for other signs of kidney damage – which can be slowed, reversed or treated if caught early enough.

The eGFR stands for the estimated glomerular filtration rate and is another important test to measure kidney function. It is calculated by blood creatinine level, age, body size, and sex.

If eGFR is low, this could mean that the kidneys are not fully functional. The normal eGFR value is greater than 90 mL/min/1.73 m2. An eGFR below 60 mL/min/1.73 m2 can indicate chronic kidney disease. eGFR values are only reported for adults.

Thyroid function test

People with type 1 diabetes with signs of thyroid gland dysfunction should have their TSH (thyroid stimulating hormone) value measured. The normal range is 0.4 to 4.0 mU/L. TSH levels increase when the thyroid gland is not producing enough thyroid hormone due to hypothyroidism, and decrease when the gland is overproducing thyroid hormone, hyperthyroidism. Both are most commonly caused by autoimmune disorders, when the immune system attacks the thyroid gland.

As T1D is also an autoimmune disease, it’s helpful to be screened for other autoimmune disorders if you are showing symptoms, but also as part of regular bloodwork.

Celiac screen

Another potential co-morbid autoimmune disease for people with T1D is Celiac’s disease. This test looks for antibodies to gluten (a type of protein found in wheat, rye, and barley), and is called the IgA-human tissue transglutaminase (TTG) test. Celiac disease occurs when the body perceives gluten as a threat and makes an antibody molecule to protect against it.

If the screening test for celiac is positive and antibodies to gluten are found, a full celiac lab evaluation is necessary to look for other antibodies directed against gluten. In addition, there are tests that can determine if someone has the common genes associated with Celiac disease. If celiac disease is diagnosed, it is treated by eliminating all gluten from the diet. This can have impacts on carb counting and insulin administration.

Being armed with more knowledge about your bloodwork results and how they relate to your T1D can help you feel more in control of your management and allow you to better advocate with your healthcare providers.

*Content adapted from materials generously provided by DiaTribe.org