Everyday Health Guide

Measures lactate (a substance produced by the body when oxygen levels are low, often indicating tissue hypoxia or severe infection). No fasting is required, but resting for 10 minutes before the draw is recommended. A standard blood draw is performed.

Measures LDH (an enzyme found in almost all body tissues, which is released into the blood when tissue is damaged). No special preparation is needed. A standard blood draw is performed.

Measures the amount of lead (a toxic heavy metal) in the blood. No fasting is required. A standard blood draw is performed. It is commonly recommended for young children or workers in high-risk industries.

Measures leptin (a hormone produced by fat cells that helps regulate energy balance and appetite). Fasting for 8–12 hours is usually required. A standard blood draw is performed.

A needle is used to remove a tiny piece of liver tissue for microscopic examination to diagnose liver disease. Fasting for several hours is required. Local anesthesia is used, and the patient must rest afterward to prevent bleeding.

A group of blood tests (including ALT, AST, ALP, and bilirubin) that provide information about the state of the liver. Fasting for 8–12 hours is usually required. A standard blood draw is performed.

Measures LDL (often called "bad" cholesterol because high levels can lead to plaque buildup in the arteries). Fasting for 9–12 hours is strictly required. A standard blood draw is performed.

A needle is inserted into the lower back to collect cerebrospinal fluid (the fluid surrounding the brain and spinal cord) to check for infections, bleeding, or neurological diseases. Local anesthesia is used. The patient must lie flat for a few hours afterward to prevent headaches.

Detects lupus anticoagulant (an antibody that paradoxically increases the risk of blood clots, despite its name). Fasting is usually not required, but blood-thinning medications may affect the result. A standard blood draw is performed.

Measures LH (a hormone produced by the pituitary gland that triggers ovulation in women and testosterone production in men). For women, it is often done on specific days of the menstrual cycle. A standard blood draw is performed.

Removes all or part of a lymph node (a small bean-shaped structure that is part of the immune system) to check for infection, lymphoma, or cancer metastasis. Local or general anesthesia is used.

Measures the amount of magnesium (a mineral essential for muscle, nerve, and heart function) in the blood. Fasting is usually not required. A standard blood draw is performed.

Uses a strong magnetic field and radio waves to create detailed images of organs and tissues. You must remove all metal objects. Fasting is only required if contrast dye is used. You lie inside a tube-like machine.

Detects the presence of malaria parasites in the blood. No fasting is required. A drop of blood is taken from a finger prick or vein and examined under a microscope.

Uses low-dose X-rays to create detailed images of the breast to screen for or diagnose breast cancer. Avoid using deodorant, powder, or lotion on the chest area on the day of the test, as they can appear as spots on the X-ray.

Measures MCH (the average amount of hemoglobin, the oxygen-carrying protein, in a single red blood cell). It is part of a standard Complete Blood Count (CBC). No fasting is required. A standard blood draw is performed.

Measures MCV (a measure of the average size of your red blood cells). It is part of a standard Complete Blood Count (CBC). No fasting is required. A standard blood draw is performed.

Measures MPV (the average size of platelets in the blood). Larger platelets are often younger and more active. It is part of a standard Complete Blood Count (CBC). No fasting is required. A standard blood draw is performed.