Traditionally performed in physician offices and laboratories, blood tests are useful tools for uncovering disorders in the human body. They detect abnormally high or low levels of substances that may indicate a variety of conditions or diseases, including skin disorders or diseases that cause symptoms related to the skin.

Blood tests may be ordered for a number of reasons, including:

• Screening for a disease before signs and symptoms appear.
  
  
• Helping determine a diagnosis. For example, a blood test may be used to find the presence of a disease that is causing generalized itching (pruritus) of the skin.
  
  
• Monitoring the progression of a disease.
  
  
• Monitoring the effectiveness and safety of a patient’s treatment, such as the use of retinoids in treating psoriasis or drugs such as itraconazole, terbinafine or fluconazole in treating fungal infections in nails.

One common blood test is a complete blood count (CBC), which measures the number of red blood cells, white blood cells, platelets and other factors in a patient’s blood sample. Other blood tests evaluate certain antibodies (e.g., antinuclear antibody), which may be used to identify skin disorders such as pemphigus.

Depending on the amount of blood required for the test, blood can be drawn from a vein puncture (venipuncture), artery puncture (arterial puncture) or skin puncture. Obtaining a blood sample only takes about five minutes, and most patients find blood tests to be virtually painless.

Most blood tests require very little preparation beforehand, and patients can generally return to their usual daily activities following testing. After a blood test, additional diagnostic tests (e.g., biopsy) may be necessary to confirm a diagnosis.