The human circulatory system, including bleeding and clotting, is far more complex than most people realize.

"For humans to survive in the world, our blood has to be able to clot quickly, but we also need the blood to stay liquid enough," points out Brian Smith, MD, chair of Yale Medicine's Department of Lab Medicine. "Our bodies have a complicated, dynamic coagulation system that helps us reach the right balance. To be healthy, both the platelet and liquid parts of the system need to be functioning properly."

If there is a malfunction and a person bleeds spontaneously or more easily or profusely than is typical, several blood tests can be done to identify what's not working.

A bleeding disorder is "basically anything that makes an individual more likely to bleed, either spontaneously just walking down the street, or more easily with slight trauma, such as a minor cut or scrape," says Dr. Smith. Many bleeding disorders are congenital, meaning they are inherited, but others are acquired over time. Bleeding disorders may also be a side effect of medication.

The most widely recognized bleeding disorder is hemophilia, though it is actually very rare. Hemophilia is a hereditary disorder that occurs when blood lacks sufficient clotting factors (also called blood-clotting proteins). Though not as well known, the most common inherited bleeding disorder is von Willebrand disease (VWD), which is caused by defects in a blood substance that helps clots form.

Bleeding disorders can affect people of any age, from babies who are just one or two days old to adults over age 90.

Potential warning signs that may indicate a person has a bleeding disorder include major bruising that results from minor bumps into things or profuse bleeding from a minor injury. Other signs include anemia, nosebleeds that are difficult to stop, too much bleeding that persists longer than usual for minor cuts and/or, for women, extremely heavy menstrual periods.

Accurate diagnosis of a bleeding disorder is important, even in a person who seems otherwise healthy. If left undiagnosed, a bleeding disorder could cause trouble during surgery or even during normal activities, says Dr. Smith.

Doctors order blood tests to identify the culprit in people with excessive bleeding and bruising. Scientists from Yale Medicine's Department of Lab Medicine work closely with doctors to analyze blood tests. According to Dr. Smith, the first step is typically a blood screening panel. "The screening approach looks at broad aspects of blood, to first give you a sense of whether the problem is with the platelet or liquid part of the blood," he explains.

According to Dr. Smith, there are more than 50 measurement tests doctors use to pinpoint the cause of a person's excessive bleeding. “Analysis of the blood is highly complex," Dr. Smith observes, adding that a typical patient may have three or four initial tests, followed by up to a dozen more to make a diagnosis. One of the most common blood tests is called a complete blood count (or CBC). This test measures the different cellular components in blood.

The PT (prothrombin time) is often given along with a PTT (partial thromboplastin time). These tests analyze different liquid parts of the blood and help diagnose problems with bleeding and blood clots.

Though Yale Medicine technicians are experts in performing and analyzing blood tests according to the latest scientific standards, the tests themselves are imperfect says Dr. Smith. “The tests are good at measuring amounts, but they're not perfect at measuring what normal looks like for each particular individual," he explains. "Results can depend on a lot of different factors, like time of day, medications a person takes, stress levels and, in women, whether or not she is pregnant.”

Other factors that can affect test results include use of pain medications, including over-the-counter aspirin. Birth control pills or hormonal fluctuations due to a woman's menstrual cycle can have an effect on blood test results. A person's blood type and/or intense exercise can also affect results.

Though there is no cure for most bleeding disorders, there are effective medications for many of them. Hematologists work with patients to determine the best treatment options, most of which involve taking drugs. These medications may be taken orally, by spray, or by shot.

Some people with bleeding disorders may only need treatment before and/or after major dental work, childbirth and/or surgery.

Yale Medicine’s Department of Laboratory Medicine offers highly specialized expertise, with physicians with advanced training in hematopathology, coagulation and transfusion medicine. These behind-the-scenes doctors work collaboratively with colleagues who care for patients directly.

The department sponsors semi-weekly conferences to discuss unique and challenging cases, Dr. Smith notes. "This gives us a huge advantage and works terrifically well."