Testing Knowledge
Test Directory
Source-backed test guides: what each test is for, how it is performed, its limitations, and which reviewed products serve it. Personal health questions are answered with knowledge and preparation guidance — not supplier sales.
Prothrombin Time Test and INR (PT/INR)
A prothrombin time (PT) test measures how many seconds it takes for a clot to form in a blood sample. Since the results of this test can vary with different labs or test methods, your results may be used to create an INR (international normalized ratio). Using this ratio makes it easier for health care providers to compare and better understand results from different labs or test methods.
Protein in Urine
A protein in urine test measures how much protein is in your urine (pee). Normally, you have very little protein in your urine. A large amount of protein in urine (proteinuria) may mean you have a kidney problem . Your kidneys are organs that filter extra water and waste out of your blood to make urine.
Protein Electrophoresis by Immunofixation Blood Test
An immunofixation (IFE) blood test measures the number and type of proteins in your blood. Proteins have many important functions, including giving your body energy, rebuilding muscles, and helping your immune system. There are different types of proteins, and each one has a different job for your body. This test checks to see if your body is making or losing too much of certain proteins. Your body might make too much or too little protein if you have certain health conditions.
Protein C and Protein S Tests
Protein C and protein S tests use a sample of your blood to measure how many of these proteins you have and how well they're working. Though they are often done together, these are separate tests. A protein C test measures protein C in your blood ; a protein S test measures protein S.
Prolactin Levels
A prolactin (PRL) test measures the level of prolactin in a sample of your blood. Prolactin is a hormone produced by the pituitary gland , a small gland at the base of the brain. Hormones are chemical messengers in your bloodstream that control the actions of certain cells or organs.
Progesterone Test
A progesterone test measures the level of progesterone in a sample of your blood. Progesterone is a hormone that's made mainly by the ovaries, which are two glands in the female reproductive system that contain eggs.
Prenatal Panel
A prenatal panel is a group of blood tests done in early pregnancy . The tests check for diseases and infections that can affect the health of you and your developing baby . The results of the tests can guide treatments, which may help prevent serious complications. A prenatal panel usually includes the following tests:
Prenatal Cell-Free DNA Screening
Prenatal cell-free DNA (cfDNA) screening is a blood test given during pregnancy . During pregnancy, some of the fetus's DNA circulates in the mother's bloodstream. A cfDNA screening checks this DNA to find out if the baby is more likely to have certain conditions caused by an abnormal number of chromosomes , such as Down syndrome .
Prealbumin Blood Test
A prealbumin blood test measures prealbumin levels in your blood. Prealbumin is a protein that's made in your liver and is found in your blood. Prealbumin is used to make other proteins and helps carry thyroid hormones and vitamin A through your bloodstream. It also helps control how your body uses energy.
Potassium Blood Test
A potassium blood test measures the amount of potassium in your blood. Potassium is a type of electrolyte . Electrolytes are electrically charged minerals that help control the amount of fluids and the balance of acids and bases (pH balance) in your body. They also help control muscle and nerve activity and perform other important functions.
Porphyrin Tests
Porphyrin tests measure the level of porphyrins in your blood, urine (pee), or stool (poop). Your body uses porphyrins to make heme. Heme is part of hemoglobin, which is a protein in your red blood cells that carries oxygen from your lungs to the rest of your body.
Pleural Fluid Analysis
A pleural fluid analysis is a group of tests that examine a sample of abnormal fluid that builds up in the space between your lungs and chest wall. This space is called the pleural space.
Platelet Tests
Platelets, also known as thrombocytes, are small blood cells. They form in your bone marrow, the sponge-like tissue in your bones. Platelets are essential for blood clotting . A blood clot is a mass of blood that forms when platelets, proteins, and cells in the blood stick together. When you get hurt, your body forms a blood clot to stop the bleeding.
Phosphate in Urine
A phosphate in urine test measures the amount of phosphate in a urine (pee) sample that you collect over a 24-hour period. Phosphate contains the mineral phosphorus. So, a phosphate test is sometimes called a phosphorus test.
Phosphate in Blood
A phosphate in blood test measures the amount of phosphate in a sample of your blood. Phosphate contains the mineral phosphorus. So, a phosphate test is sometimes called a phosphorus test.
Phenylketonuria (PKU) Screening
A PKU screening test measures the amount of a protein called phenylalanine (Phe) in a sample of a newborn's blood. Phe is in all foods that contain protein such as milk, meats, and nuts. It's also in an artificial sweetener called aspartame. If a newborn has high levels of Phe in their blood, it could mean that they have phenylketonuria (PKU).
Pharmacogenetic Tests
Pharmacogenetics (also called pharmacogenomics ) is the study of how your genes affect the way your body responds to certain medicines . Genes are parts of DNA in your cells that you inherit from your parents. You inherit two copies of each gene, one from each parent. Genes carry information that controls what you look like and how your body works.
PDL1 (Immunotherapy) Tests
A PD-L1 test uses a sample of cancerous tumor tissue to measure how much of a protein called programmed-death ligand 1 (PD-L1) is found on the cancer cells. Normally, PD-L1 is found on certain healthy cells. It helps keep your immune system from attacking healthy tissue by acting as a kind of "brake" on your immune system cells (called T-cells). However, in some cancers, PD-L1 keeps your immune system from attacking cancerous cells.
PCR Tests
PCR (polymerase chain reaction) tests are a reliable and accurate way to diagnose certain infectious diseases , some types of cancer , and certain genetic changes. The tests check for small amounts of genetic material of a pathogen (disease-causing organism) or abnormal cells in a sample of your blood, saliva, mucus, or tissue. The genetic material could be:
Partial Thromboplastin Time (PTT) Test
A partial thromboplastin time (PTT) test uses a blood sample to measure the number of seconds it takes for your blood to clot . Normally, when you get a cut or injury that causes bleeding, many different types of proteins in your blood work together to make a clot to stop the bleeding. These proteins are called coagulation factors or clotting factors, and your liver makes most of them.
Parathyroid Hormone (PTH) Test
This test measures the level of parathyroid hormone (PTH) in your blood. PTH, is made by your parathyroid glands . They are four pea-sized glands in your neck.
Parainfluenza Tests
A parainfluenza test checks a fluid sample from your nose or lungs for the four types of parainfluenza viruses (also called human parainfluenza viruses, or HPIVs). These viruses are a common cause of respiratory (breathing) illnesses, especially in spring, summer, and fall.
Ova and Parasite Test
An ova and parasite test looks for intestinal parasites and their eggs (ova) by checking a sample of your stool (poop) under a microscope. The test is also called an O&P.
Osmolality Tests
Osmolality tests measure the amount of certain substances in your blood, urine, or stool (poop). The tests can show how your kidneys are working and whether you have an unhealthy fluid balance .