Diagnosis using hematopathology.
Testing of blood is both a diagnostic test and useful for monitoring the progress or treatment of a condition, after its diagnosis, as an interval check during on-going therapy to monitor the efficacy of treatment.
Studying blood under the microscope can identify misshapen cells (e.g., sickle cells), damages cells (fragments seen from turbulence in the blood stream), and abnormal appearing cells (speckled, dark, faint, etc.) that diagnose specific disorders.
Blood as a tissue can also develop malignancy. The microscopic examination of blood may show first signs of conditions like leukemia, lymphoma, multiple myeloma, and bone cancer.
Culture of the blood can identify bacteria there, which is a prerequisite condition for sepsis, a life-threatening infection in the blood which can lead to shock. The bacteria that are grown can be tested against several antibiotics in order to drive therapeutic decisions.
The “complete blood count” is a test of the cellular parts in the blood. Red blood cells (RBC) contain hemoglobin, and a deficiency in RBC numbers is anemia. Anemia will limit the amount of oxygen carried to tissues. The red cells, in a CBC, can be categorized as to their size, volume, and hemoglobin capacity.
- White blood cells count (WBC): The “leukocyte” count is the number of immune cells that have varied functions, from releasing toxic substances to destroying invaders by engulfing them (“phagocytosis”). A rise in their numbers indicates a call to action by the immune system, i.e., infection. A decrease in their numbers implies immunocompromise or immunosuppression, often used as a warning to stop chemotherapy or seen in immunosuppressive diseases such as HIV/AIDS.
- WBC differential: In addition to a total count of the white blood cells, the leukocyte population is broken down as to type, useful in identifying an acute infection vs. a chronic one. It can also, based on the type of white blood cell that proliferates over the others, tell the difference between a viral infection and a bacterial infection or identify allergies and gastrointestinal conditions.
- Platelet count: Platelets (“thrombocytes”) are a component in the blood clotting system, and platelet count is often decreased in many illnesses, making bleeding disorders more likely.
Platelets are not the only part of the clotting cascade that is part of healing. Coagulation studies not only identify where in that complex sequence clotting can go wrong, but how affected the clotting is by medication used to slow it down, such as in thromboembolic disease.
The metabolic profile can be partial, as in a direct measurement of specific components, or complete, which can include blood glucose levels, liver function enzyme evaluation, electrolytes (sodium, potassium, calcium), kidney function elements, bilirubin that can indicate obstructive liver disease, and other tests. Hemoglobin A1c is a type of specialized diabetic test that can give a global picture (long-term average) of glycemic control.
There are different blood types that will either cooperate with transfusions or react immunologically as a life-threatening transfusion reaction. A type-and-screen will judge a patient’s blood type and Rh-factor, and a type-and-match will test it against proposed donor or recipient blood to avoid a transfusion reaction. These identify antibodies whose presence are important to recognize before any transfusion.
Certain tissue damage will release specific substances unique to that particular tissue, called biomarkers. The presence or rise of them is used to diagnose cardiac disease, muscle damage, and others. There are also biomarkers that are released my malignant cells in many cancers.
Suspicion of a specific infection (viral, bacterial, fungal, etc.) can be explored with blood tests. Tests for antibodies (made by the body) indicate exposure to a specific infectious agent; tests for antigens (the actual infectious agent) identifies on-going (current) infection and can be used via “titers” to judge the progression or remission during treatment.
Hepatitis B and C, HIV, and other viral infections can be quantitated in the body by a count of the viral load, the number of viruses in a millimeter of blood.
Pregnancy tests, thyroid function and other endocrine tests, kidney function, and diagnosis of menopause, ovarian function, and fertility conditions are easily investigated via simple blood tests.
Blood can be used to retrieve a patient’s DNA for genetic evaluation into rare, inherited disorders. The DNA can also identify mutations as a screen of those at risk for related malignancies, such as the BRCA I and II mutations in ovarian, uterine, and gastrointestinal cancer.