Everyone is bound to get blood work done at some point in their lives. Whether it be a general check-up or a screening for possible diagnoses, blood tests reveal significant insights about our health. For instance, a blood test can determine if someone’s iron levels are deficient or within the normal range, as well as any other nutrient.
Fasting is the abstention from food and beverages for 8-12 hours before a blood test. It is a standard procedure for patients to conduct prior to a blood draw. However, each blood test differs, and it is essential for a phlebotomist to learn which tests require fasting, whether or not the patient can drink liquids, and the fasting period’s length. That way they can inform a patient about what they need to do to prepare for their blood test in order to have accurate results.
Blood tests give doctors an understanding and baseline of one’s health. However, when a patient consumes foods and/or drinks before a blood test, it can interfere with a body’s typical nutrient levels. For example, if a patient is hypoglycemic, eating foods before a blood test could spike their blood sugar levels, inhibiting the physician’s ability to detect abnormalities and correctly diagnose their condition. It is difficult for the physician to distinguish whether it is a behavior that influences the results (e.g., eating food to help your hypoglycemia) or if they are genuinely at a normal range (e.g., not being hypoglycemic).
If a patient doesn’t not fast, notify their care provider immediately. Depending on the test and the physician, alternate tests may be available, or they will have to reschedule the appointment. It is always better to reschedule an appointment than a patient to receive an incorrect diagnosis and improper treatment plan.
Here are the blood tests that require fasting:
- Blood Glucose Test. This blood test measures our blood sugar levels. Fasting time: 8 to 10 hours.
- Gamma Glutamyl Transferase (GGT). This test measures the GGT enzyme and liver health. Fasting time: 8 to 10 hours.
- Glucose Tolerance Test. This test evaluates blood sugar levels. Fasting time: 8 to 12 hours.
- Liver Function Test. This test gathers information about the enzymes and nutrients in the liver. Fasting time: 8 to 12 hours.
- Renal Function Test. This blood test assesses kidney functioning and the body’s ability to dispose of its waste. Fasting time: 8 to 12 hours.
- Vitamin B12 Test. This test evaluates whether people are deficient in vitamin B12 or not and its impacts. Fasting time: 8 to 12 hours.
- Lactose Tolerance Test. This test determines if people can tolerate and consume dairy products. Fasting time: 8 to 12 hours.
While most tests ask for patients to fast for 8 to 10 hours, there are a few that require 12 hours of fasting, including the following:
- Lipid Profile. This blood test assesses the amount of cholesterol and triglycerides in our blood. Fasting time: 12 hours.
- Thyroid Function Test. This test measures thyroid hormones, which are heavily impacted by our diet. Fasting time: 12 hours.
- Iron Test. This test analyzes one’s iron levels, particularly to diagnose people with anemia. Fasting time: 12 hours.
Patients should not fast for longer than 12 hours. While fasting is critical to these blood tests’ reliability and validity, over fasting can result in dehydration or other side effects. When fasting, remind patients that sleep also counts as fasting. For instance, if they have an 8 AM appointment, sleeping from 9 PM to 7 AM counts as 10 hours of fasting, as long as they do not eat in the morning before the appointment.
Fasting is not solely abstaining from food. When fasting, patients are often not permitted to drink any beverage aside from water. Although patients may perceive liquids to be different from food, they can still impact the test results’ credibility. For instance, drinking orange juice can influence one’s vitamin C levels, potentially producing false data. It is critical not to consume a beverage, such as orange juice, because the test results cannot distinguish whether someone’s enzymes are within normal range or were impacted by the beverage’s vitamins, minerals or sugar. Overall, people should avoid coffee, tea, soda, alcohol and juices before a blood test.
Keep in mind, it is important for patients to stay hydrated through drinking water as it makes blood drawing easier.
In addition to beverages, a patient should also avoid:
- Chewing gum
- Taking supplements and multivitamins
- Strenuous exercise
- Certain medications – Regarding drug use, make sure a patient has consulted with their doctor before fasting to see if they should take their medications. Most medications are usually fine but some may need to be avoided if they need to be taken with food.
At PhlebotomyU, we teach our students about each blood test through our CPT-1 course. Students gain valuable knowledge and practical experience through 80+ hours in the classroom and 40+ hours in the field. To learn more about our CPT-1 course, contact PhlebotomyU today.