This test measures the level of prostate-specific antigen (PSA) in your blood. If your PSA levels start to rise, you may have prostate cancer.

The protoporphyrin test is used to diagnose blood problems caused by lead. The test can show lead exposure or lead poisoning.

This test measures levels of protein S, a protein in the blood that helps it to clot.

Protein electrophoresis is a test that measures specific proteins in the blood.

This test measures the level of protein C in your blood. If you have too little protein C, called a protein C deficiency, it means that your blood may clot too much.

This test measures the level of prolactin in your blood. The test can help find out if you have a pituitary gland tumor.

This blood test measures proinsulin, a building block for insulin. Measuring proinsulin in your blood can help figure out your risk for type 1 or type 2 diabetes.

This test measures the level of a hormone called progesterone in your blood. You may need this test if you are having trouble getting pregnant.

The prealbumin screen is a blood test to see whether you are getting enough protein in your diet.

This test measures the amount of potassium in your blood. It's often part of a routine blood test to check your level of electrolytes.