Laboratory Tests–Blood Tests
Blood tests can be used to diagnose and monitor a variety of urologic conditions. In many cases, the results of blood work can help doctors determine if further lab tests or treatments are necessary.
Blood testing is a routine procedure. A blood test involves using a needle to collect blood, usually from a vein in the arm. This blood sample is then sent to a laboratory for analysis.
Substances in the blood are measured in either milligrams per deciliter (mg/dL) or nanograms per milliliter (ng/mL). Normal ranges are given as guidelines, but these levels can vary among laboratories. Abnormal test results do not necessarily mean that the patient has a urologic condition. Doctors confirm unusual results by repeating the blood test or performing a combination of different diagnostic tests.
Here are some common blood tests that health care providers use to help diagnose urologic conditions:
- Blood urea nitrogen (BUN) test—This test, which is used to evaluate kidney function, diagnose kidney problems, and monitor dialysis results, involves measuring the level of nitrogen in the urea of the blood. Urea is a waste product that forms when protein breaks down. Usually, the kidneys filter urea and the substance passes from the body in the urine. However, kidney problems can interfere with this filtering and lead to higher levels of urea nitrogen. The normal range for this test is 7 to 20 mg/dL.
- Creatinine test—Creatinine (Cr) forms when a substance found in muscle tissue breaks down. Like urea nitrogen, the kidneys filter out creatinine and let it pass through urine. A high level of creatinine in the blood may indicate kidney damage caused by kidney infection, kidney stones, or decreased blood flow to the kidneys. Abnormal test results also may suggest dehydration or a urinary blockage. The normal range for this test is 0.8 to 1.4 mg/dL.
- Prostate-specific antigen (PSA) test—This test may be used in men to screen for prostate cancer (beginning at the age of 50 or at age 40 if at higher risk) and to monitor prostate cancer treatment. PSA is a protein produced by the prostate gland. The PSA test also may be used to diagnose benign prostatic hyperplasia (BPH, enlarged prostate) and or prostate infection (prostatitis) in men. Urinary tract infection (UTI) can affect the results of this test and cause an abnormally high reading.
For most men, the normal range for the PSA test is lower than 4.0 ng/mL; however, there is no specific normal or abnormal level. Men at increased risk for prostate cancer may be retested if their level is higher than 2.5 ng/mL. High PSA levels do not mean that a patient has prostate cancer, but may prompt further testing or a prostate biopsy.
The free PSA test is a variation of the usual PSA test. Normally, the protein PSA can be found in two forms in the blood—either attached to other proteins or "free" (unattached). The free PSA test measures the amount of PSA that is unattached. The results of this test can provide further clues on the likelihood of prostate cancer—a high level of overall PSA, but low level of free PSA indicates a greater risk for cancer of the prostate.
- Calcium test—This test, which measures the level of calcium in the blood, can be used to screen patients for kidney disease. The normal range for this test is 8.5 to 10.2 mg/dL. A lower-than-normal test result might indicate kidney failure.
- Phosphate (phosphorus) test—Phosphate tests, which measure phosphate levels in the blood, are used to diagnose kidney problems and monitor dialysis. The normal range for this test is 2.4 to 4.1 mg/dL. Levels that are higher or lower-than-normal may indicate kidney disease.
- Alpha-fetoprotein (AFP) and beta-human chorionic gonadotropin (beta-hCG) tests—These tests are used to help diagnose testicular cancer. AFP and beta-hCG are substances that are produced in higher-than-normal amounts by testicular cancer cells.