Common Lab Test Changes You Should Know

Medically Reviewed by Michael W. Smith, MD on November 15, 2019

A visit to the doctor often includes a visit to the lab for blood tests. But the last few years have brought changes to how some common lab tests are done.

This test looks at lipids (also called blood fats), including total cholesterol, high-density lipoprotein (HDL or “good” cholesterol), low-density lipoprotein (LDL or “bad” cholesterol), and triglycerides. The results of this test often help predict risk of heart disease and stroke.

What’s changed? Traditionally, patients needed to fast prior to this test because doctors believed food could impact these levels. But fasting is not required for most people. Certain foods can impact triglyceride levels, so if the test comes back high, you might need to do the test again while fasting. But most patients can skip the fast.

More than 23 million U.S. adults have diabetes and another 7 million have diabetes and do not know it. Another 84 million have prediabetes, a condition often related to obesity that puts a person at much higher risk for developing the disease. Therefore, it is important to get the right test to determine if you have diabetes.

Recently, many physicians have ordered the hemoglobin A1c blood sugar test for this purpose. In the past it was used for helping manage medication doses. But around 2012, several organizations began to add it as a diagnostic test. Many doctors and patients prefer it over the oral glucose tolerance test, which requires an overnight fast and takes more than 2 hours.

The hemoglobin A1c test measures glucose that sticks to hemoglobin, part of the red blood cells that carry oxygen to the body. It gives an average glucose reading over the course of the life of the red blood cell, which is around 90 to 120 days.

However, we have recently learned that if you have certain conditions that might affect red blood cells, such as anemia or sickle cell disease (more common in African Americans than other ethnicities), the hemoglobin A1c test might not be completely accurate. In some instances, it might register artificially high. It’s important to remember that there are numerous factors that affect blood sugar, so it’s important to talk to your doctor about the results.

This mostly matters when the test results are close to the normal cutoffs, since that can make diagnosis more challenging. You may need additional blood sugar tests, both fasting and nonfasting, to help with diagnosis.

Many people used to give a yearly urine sample (called a urinalysis) to test for infections and assess kidney function. Now, the U.S. Preventive Services Task Force does not recommend a urinalysis unless you have symptoms such as burning, pain, urgency, or bad odor. (Note that this recommendation doesn’t apply to pregnant women, who should get frequent urine tests as part of their routine obstetrics care.)

For kidney function, physicians now largely rely on a test called the EGFR (estimated glomerular filtration rate), which is calculated as part of a basic metabolic panel, a standard blood test, that helps your doctor determine if your kidneys are working properly.

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European Heart Journal: "Fasting is not routinely required for determination of a lipid profile: clinical and laboratory implications including flagging at desirable concentration cut-points—a joint consensus statement from the European Atherosclerosis Society and European Federation of Clinical Chemistry and Laboratory Medicine."

NIH: " Fasting or Non-fasting Lipids for Atherosclerotic Cardiovascular Disease Risk Assessment and Treatment?" "Nonfasting versus fasting lipid profile for cardiovascular risk prediction," "Glycated haemoglobin (HbA1c) for the diagnosis of diabetes," "Disparities in HbA1c Levels Between African-American and Non-Hispanic White Adults With Diabetes."

CDC: "National Diabetes Statistics Report."

Medical Journal of Australia: "The role of HbA1c in the diagnosis of diabetes mellitus in Australia."

Annals of Internal Medicine: "The role of HbA1c in the diagnosis of diabetes mellitus in Australia"

JAMA: "Association of Sickle Cell Trait With Hemoglobin A1c in African Americans."

PLos: "Impact of common genetic determinants of Hemoglobin A1c on type 2 diabetes risk and diagnosis in ancestrally diverse populations: A transethnic genome-wide meta-analysis."

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