In DIC, the underlying cause usually leads to symptoms and signs, and DIC is discovered on laboratory testing. The onset of DIC can be sudden, as in endotoxic shock or amniotic fluid embolism, or it may be insidious and chronic, as in cancer. DIC can lead to multiorgan failure and widespread bleeding.

Disseminated intravascular coagulation (DIC) is a condition in which blood clots form throughout the body blocking small blood vessels. Symptoms may include chest pain, shortness of breath, leg pain, problems speaking, or problems moving parts of the body. As clotting factors and platelets are used up, bleeding may occur. This may include blood in the urine, blood in the stool, or bleeding into the skin. Complications may include organ failure.

Relatively common causes include sepsis, surgery, major trauma, cancer, and complications of pregnancy. Less common causes include snake bites, frostbite, and burns. There are two main types acute (rapid onset) and chronic (slow onset). Diagnosis is typically based on blood tests. Findings may include low platelets, low fibrinogen, high INR, or high D-dimer.

Treatment is mainly directed towards the underlying condition. Other measures may include giving platelets, cryoprecipitate, or fresh frozen plasma. Evidence to support these treatments, however, is poor. Heparin may be useful in the chronic form. About 1% of people admitted to hospital are affected by the condition. In those with sepsis rates are between 20% and 50%. The risk of death among those affected varies from 20 to 50%.

The signs and symptoms of TTP may at first be subtle and nonspecific. Many people experience an influenza-like or diarrheal illness before developing TTP. Neurological symptoms are very common and vary greatly in severity. Frequently reported symptoms include feeling very tired, confusion, and headaches. Seizures and symptoms similar to those of a stroke can also be seen.

As TTP progresses, blood clots form within small blood vessels (microvasculature), and platelets (clotting cells) are consumed. As a result, bruising, and rarely bleeding can occur. The bruising often takes the form of purpura, while the most common site of bleeding, if it occurs, is from the nose or gums. Larger bruises (ecchymoses) may also develop.

The classic presentation of TTP includes a constellation of five medical signs which classically support the clinical diagnosis of TTP, although it is unusual for patients to present with all 5 symptoms. The pentad includes:

- Fever

- Changes in mental status

- Thrombocytopenia

- Reduced kidney function

- Haemolytic anaemia (microangiopathic hemolytic anemia).

High blood pressure (hypertension) may be found on examination.

The clinical presentation of TMA, although dependent on the type, typically includes: fever, microangiopathic hemolytic anemia (see schistocytes in a blood smear), renal failure, thrombocytopenia and neurological manifestations. Generally, renal complications are particularly predominant with Shiga-toxin-associated hemolytic uremic syndrome (STx-HUS) and atypical HUS, whereas neurologic complications are more likely with TTP. Individuals with milder forms of TTP may have recurrent symptomatic episodes, including seizures and vision loss. With more threatening cases of TMA, and also as the condition progresses without treatment, multi-organ failure or injury is also possible, as the hyaline thrombi can spread to and affect the brain, kidneys, heart, liver, and other major organs.

Thrombotic microangiopathy (TMA) is a pathology that results in thrombosis in capillaries and arterioles, due to an endothelial injury. It may be seen in association with thrombocytopenia, anemia, purpura and renal failure.

The classic TMAs are hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. Other conditions with TMA include atypical hemolytic uremic syndrome, disseminated intravascular coagulation, scleroderma renal crisis, malignant hypertension,

antiphospholipid antibody syndrome, and drug toxicities, e.g. calcineurin inhibitor toxicity.

Thrombotic thrombocytopenic purpura (TTP) is a rare disorder of the blood-coagulation system, causing extensive microscopic clots to form in the small blood vessels throughout the body, resulting in low platelet counts. These small blood clots, called thrombi, can damage many organs including the kidneys, heart, brain, and nervous system. In the era before effective treatment with plasma exchange, the fatality rate was about 90%. With plasma exchange, this has dropped to 10% at six months. Because the disease generally results from antibodies that activate the immune system to inhibit the ADAMTS13 enzyme, agents that suppress the immune system, such as glucocorticoids, rituximab, cyclophosphamide, vincristine, or ciclosporin, may also be used if a relapse or recurrence follows plasma exchange. Platelets are not transfused unless the patient has a life-threatening bleed, since the transfused platelets would also quickly be consumed by thrombi formation, leading to a minimal increase in circulating platelets.

Most cases of TTP arise from autoantibody-mediated inhibition of the enzyme ADAMTS13, a metalloprotease responsible for cleaving large multimers of von Willebrand factor (vWF) into smaller units. The increase in circulating multimers of vWF increases platelet adhesion to areas of endothelial injury, particularly where arterioles and capillaries meet, which in turn results in the formation of small platelet clots called thrombi. As platelets are used up in the formation of thrombi, this then leads to a decrease in the number of overall circulating platelets, which may then cause life-threatening bleeds. The reason why the antibodies form is generally unknown for most patients, though it can be associated with some medications and autoimmune diseases such as HIV and Lupus, as well as pregnancy.

A rarer form of TTP, called Upshaw–Schulman syndrome, or "Inherited TTP," results from an autosomal recessive gene that leads to ADAMTS13 dysfunction from the time of birth, resulting in persisting large vWF multimers, which in turn results in the formation of thrombi (small platelet clots).

Red blood cells passing the microscopic clots are subjected to shear stress, which damages their membranes, leading to rupture of red blood cells within blood vessels, which in turn leads to anaemia and schistocyte formation. The presence of these blood clots in the small blood vessels reduces blood flow to organs resulting in cellular injury and end organ damage. Current therapy is based on support and plasmapheresis to reduce circulating antibodies against ADAMTS13 and replenish blood levels of the enzyme.

The most important differential diagnosis is disseminated intravascular coagulation, which is characterized with similar features but presence of a low platelet count and microcirculatory thrombosis. Antifibrinolytic treatments are contraindicated in patients with disseminated intravascular coagulation while they are useful in the treatment of primary fibrinogenolysis.

While there are several possible causes, they generally result in excessive bleeding and a lack of clotting.

Early purpura fulminans lesions look similar to traumatic skin bleeds or purpuric rashes, such as immune thrombocytopenic purpura or thrombotic thrombocytopenic purpura; however, purpura fulminans will rapidly progress to necrosis whereas other purpuric rashes do not. In most cases, differential diagnoses may be distinguished from purpura fulminans by other clinical and laboratory findings.

The initial appearance of purpura fulminans lesions is of well-demarcated erythematous lesions which progress rapidly to develop irregular central areas of blue-black haemorrhagic necrosis. Advancing areas of necrosis are often surrounded by a thin border of erythema that fades into adjacent unaffected skin. Haemorrhage into the necrotic skin causes purpura fulminans lesions to become painful, dark and raised, sometimes with vesicle or blister (bulla) formation.

The distribution of purpura fulminans lesions may be different according to the underlying pathogenesis. Purpura fulminans in severe sepsis typically develops in the distal extremities and progresses proximally or appears as a generalised or diffuse rash affecting the whole body surface. In cases of severe inheritable protein C deficiency, purpura fulminans with disseminated intravascular coagulation manifests within a few hours or days after birth.

In medicine (hematology), bleeding diathesis (h(a)emorrhagic diathesis) is an unusual susceptibility to bleed (hemorrhage) mostly due to hypocoagulability, in turn caused by a coagulopathy (a defect in the system of coagulation). Several types are distinguished, ranging from mild to lethal. Also, bleeding diathesis can be caused by thinning of the skin or impaired wound healing.

Purpura fulminans is an acute, often fatal, thrombotic disorder which manifests as blood spots, bruising and discolouration of the skin resulting from coagulation in small blood vessels within the skin and rapidly leads to skin necrosis and disseminated intravascular coagulation.

Primary fibrinogenolysis is the pathological lysis of fibrinogen characterized with a low fibrinogen, high fibrin degradation products, prolonged prothrombin time and activated partial thromboplastin time, a normal platelet count and absence of microcirculatory thrombosis.

Thrombocytopenia usually has no symptoms and is picked up on a routine full blood count (or complete blood count). Some individuals with thrombocytopenia may experience external bleeding such as nosebleeds, and/or bleeding gums. Some women may have heavier or longer periods or breakthrough bleeding. Bruising, particularly purpura in the forearms and petechiae in the feet, legs, and mucous membranes, may be caused by spontaneous bleeding under the skin.

Eliciting a full medical history is vital to ensure the low platelet count is not secondary to another disorder. It is also important to ensure that the other blood cell types, such as red blood cells and white blood cells, are not also suppressed.

Painless, round and pinpoint (1 to 3 mm in diameter) petechiae usually appear and fade, and sometimes group to form ecchymoses. Larger than petechiae, ecchymoses are purple, blue or yellow-green areas of skin that vary in size and shape. They can occur anywhere on the body.

A person with this disease may also complain of malaise, fatigue and general weakness (with or without accompanying blood loss). Acquired thrombocytopenia may be associated with a history of drug use. Inspection typically reveals evidence of bleeding (petechiae or ecchymoses), along with slow, continuous bleeding from any injuries or wounds. Adults may have large, blood-filled bullae in the mouth. If the person's platelet count is between 30,000 and 50,000/mm, bruising with minor trauma may be expected; if it is between 15,000 and 30,000/mm, spontaneous bruising will be seen (mostly on the arms and legs).

STEC-HUS occurs after ingestion of a strain of bacteria expressing Shiga toxin(s), usually types of "E. coli", that expresses verotoxin (also called Shiga-like toxin). "E. coli" can produce stx1 and/or stx2 Shiga toxins, the latter being more dangerous and a combination of both toxins in certain ratios is usually associated with HUS. These Shiga toxins bind GB3 receptors, globotriaosylceramide, which are present in renal tissue more than any other tissue and are also found in central nervous system neurons and other tissue. Children have more GB3 receptors than adults which may be why children are more susceptible to HUS. Cattle, swine, deer, and other mammals do not have GB3 receptors, but can be asymptomatic carriers of Shiga toxin-producing bacteria. Some humans can also be asymptomatic carriers. Once the bacteria colonizes, diarrhea followed by bloody diarrhea, hemorrhagic colitis, typically follows. HUS develops about 5–10 days after onset of diarrhea, with decreased urine output (oliguria), blood in the urine (hematuria), kidney failure, thrombocytopenia (low levels of platelets) and destruction of red blood cells (microangiopathic hemolytic anemia). Hypertension is common. In some cases, there are prominent neurologic changes.

Patients with HUS commonly exhibit the signs and symptoms of thrombotic microangiopathy (TMA), which can include abdominal pain, low platelet count, elevated lactate dehydrogenase LDH, a chemical released from damaged cells, and which is therefore a marker of cellular damage) decreased haptoglobin (indicative of the breakdown of red blood cells) anemia (low red blood cell count)/schistocytes (damaged red blood cells), elevated creatinine (a protein waste product generated by muscle metabolism and eliminated renally, proteinuria (indicative of kidney injury), confusion, fatigue, edema (swelling), nausea/vomiting, and diarrhea. Additionally, patients with aHUS typically present with an abrupt onset of systemic signs and symptoms such as acute kidney failure, hypertension (high blood pressure), myocardial infarction (heart attack), stroke, lung complications, pancreatitis (inflammation of the pancreas), liver necrosis (death of liver cells or tissue), encephalopathy (brain dysfunction), seizure, and coma. Failure of neurologic, cardiac, renal, and gastrointestinal (GI) organs, as well as death, can occur unpredictably at any time, either very quickly or following prolonged symptomatic or asymptomatic disease progression.

Thrombocytopenia is a condition characterized by abnormally low levels of thrombocytes, also known as platelets, in the blood.

A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. These limits are determined by the 2.5th lower and upper percentile, so values outside this range do not necessarily indicate disease. One common definition of thrombocytopenia requiring emergency treatment is a platelet count below 50,000 per microliter.

Individuals with congenital hypfibringenemia often lack any symptoms are detected by routine lab testing of fibrinogen or when tested for it because close relatives have symptomatic hypofibrinogenmeia. Indeed, studies indicate that, among family members with the identical congenital hypofibrinogenemia mutation, some never exhibit symptoms and those that are symptomatic develop symptoms only as adults.

Individuals with this disorder are usually less symptomatic than patients with other fibrinogen disorders because their fibrinogen levels are generally sufficient to prevent spontaneous bleeding. Those with particularly low blood fibrinogen levels (<0.5 gram/liter) may develop serious bleeding spontaneously and many with the disorder do so following trauma or surgery. Depending on their fibrinogen levels, women with the disorder may also bleed excessively during delivery and the postpartum period; in rare cases, they may have an increased risk of suffering miscarriages. Individuals with the disorder also suffer thrombotic events which may include blockage of large arteries in relatively young patients who have high levels of cardiovascular risk factors. The thrombi which form in these individuals are unstable, tend to embolize, and may therefore lead to thromboembolic events such as pulmonary embolism. Both bleeding and thrombotic events can occur at separate times or even concurrently in the same individual with the disorder.

There are various symptoms that are presented and are typically associated to a specific site that they appear at. Hypoprothrombinemia is characterized by a poor blood clotting function of prothrombin. Some symptoms are presented as severe, while others are mild, meaning that blood clotting is slower than normal. Areas that are usually affected are muscles, joints, and the brain, however, these sites are more uncommon.

The most common symptoms include:

1. Easy bruising

2. Oral mucosal bleeding - Bleeding of the membrane mucus lining inside of the mouth.

3. Soft tissue bleeding.

4. Hemarthrosis - Bleeding in joint spaces.

5. Epistaxis - Acute hemorrhages from areas of the nasal cavity, nostrils, or nasopharynx.

6. Women with this deficiency experience menorrhagia: prolonged, abnormal heavy menstrual bleeding. This is typically a symptom of the disorder when severe blood loss occurs.

Other reported symptoms that are related to the condition:

1. Prolonged periods of bleeding due to surgery, injury, or post birth.

2. Melena - Associated with acute gastrointestinal bleeding, dark black, tarry feces.

3. Hematochezia - Lower gastrointestinal bleeding, passage of fresh, bright red blood through the anus secreted in or with stools. If associated with upper gastrointestinal bleeding, suggestive of a more life-threatening issue.

Type I: Severe hemorrhages are indicators of a more severe prothrombin deficiency that account for muscle hematomas, intracranial bleeding, postoperative bleeding, and umbilical cord hemorrhage, which may also occur depending on the severity, respectively.

Type II: Symptoms are usually more capricious, but can include a variety of the symptoms described previously. Less severe cases of the disorder typically do not involve spontaneous bleeding.

The presentation of TTP is variable. The initial symptoms, which force the patient to medical care, are often the consequence of lower platelet counts like purpura (present in 90% of patients), ecchymosis and hematoma. Patients may also report signs and symptoms as a result of (microangiopathic) hemolytic anemia, such as (dark) beer-brown urine, (mild) jaundice, fatigue and pallor. Cerebral symptoms of various degree are present in many patients, including headache, paresis, speech disorder, visual problems, seizures and disturbance of consciousness up to coma. The symptoms can fluctuate so that they may only be temporarily present but may reappear again later in the TTP episode. Other unspecific symptoms are general malaise, abdominal, joint and muscle pain. Severe manifestations of heart or lung involvements are rare, although affections are not seldom measurable (such as ECG-changes).

Hemolytic-uremic syndrome (or haemolytic-uraemic syndrome), abbreviated HUS, is a disease characterized by a triad of hemolytic anemia (anemia caused by destruction of red blood cells), acute kidney failure (uremia), and a low platelet count (thrombocytopenia). It predominantly, but not exclusively, affects children. Most cases are preceded by an episode of infectious, sometimes bloody, diarrhea acquired as a foodborne illness or from a contaminated water supply caused by , other non-O157:H7 "E. coli" serotypes, "Shigella", and "Campylobacter". A variety of viruses have also been implicated as a causative agent. It is now the most common cause of acquired acute renal failure in childhood. It is a medical emergency and carries a 5–10% mortality rate; of the remainder, the majority recover without major consequences, approximately 30% suffer residual renal injury. The primary target appears to be the vascular endothelial cell. This may explain the pathogenesis of HUS, in which a characteristic renal lesion is capillary microangiopathy.

HUS was first defined as a syndrome in 1955. The more common form of the disease, Shiga-like toxin-producing "E. coli" HUS (STEC-HUS), is triggered by the infectious agent "E. coli" O157:H7, and several other non-O157:H7 "E. coli" serotypes. Certain Shiga toxin-secreting strains of "Shigella dysenteriae" can also cause HUS. Approximately 5% of cases are classified as pneumococcal HUS, which results from infection by "Streptococcus pneumoniae", the agent that causes traditional lobar pneumonia. There is also a rare, chronic, and severe form known as atypical hemolytic uremic syndrome (aHUS), which is caused by genetic defects resulting in chronic, uncontrolled complement activation. Both STEC-HUS and aHUS cause endothelial damage, leukocyte activation, platelet activation, and widespread inflammation and multiple thromboses in the small blood vessels, a condition known as systemic thrombotic microangiopathy (TMA), which leads to thrombotic events as well as organ damage/failure and death.

In medicine (hematology) microangiopathic hemolytic anemia (MAHA) is a microangiopathic subgroup of hemolytic anemia (loss of red blood cells through destruction) caused by factors in the small blood vessels. It is identified by the finding of anemia and schistocytes on microscopy of the blood film.

In diseases such as hemolytic uremic syndrome, disseminated intravascular coagulation, thrombotic thrombocytopenic purpura, and malignant hypertension, the endothelial layer of small vessels is damaged with resulting fibrin deposition and platelet aggregation. As red blood cells travel through these damaged vessels, they are fragmented resulting in intravascular hemolysis. The resulting schistocytes (red cell fragments) are also increasingly targeted for destruction by the reticuloendothelial system in the spleen, due to their narrow passage through obstructed vessel lumina. It is seen in systemic lupus erythematosus, where immune complexes aggregate with platelets, forming intravascular thrombi. Microangiopathic hemolytic anemia is also seen in cancer.

Automated analysers (the machines that perform routine full blood counts in most hospitals) are generally programmed to flag blood films that display red blood cell fragments or "schistocytes".

HELLP usually begins during the third trimester; rare cases have been reported as early as 21 weeks gestation. Often, a woman who develops HELLP syndrome has already been followed up for pregnancy-induced hypertension (gestational hypertension), or is suspected to develop pre-eclampsia (high blood pressure and proteinuria). Up to 8% of all cases occur after delivery.

Women with HELLP syndrome often appear non-toxic. Early symptoms can include:

- In 90% of cases, either epigastric pain described as "heartburn" or right upper quadrant pain develops.

- In 90% of cases, malaise occurs.

- In 50% of cases, nausea or vomiting happen.

Gradual but marked onset of headaches (30%), blurred vision, and paresthesia (tingling in the extremities) can occur. Edema may occur, but its absence does not exclude HELLP syndrome. Arterial hypertension is a diagnostic requirement, but may be mild. Rupture of the liver capsule and a resultant hematoma may occur. If a woman has a seizure or coma, the condition has progressed into full-blown eclampsia.

Disseminated intravascular coagulation is also seen in about 20% of all women with HELLP syndrome, and in 84% when HELLP is complicated by acute renal failure. Pulmonary edema is found in 6% of all women with HELLP syndrome, and when HELLP is complicated by acute renal failure, pulmonary edema is found in 44% of women with the syndrome.

A woman with symptoms of HELLP can be misdiagnosed in the early stages, increasing the risk of liver failure and morbidity. Rarely, after a caesarean section surgery, a woman may have signs and symptoms of a shock condition mimicking either pulmonary embolism or reactionary haemorrhage.

Purpura are a common and nonspecific medical sign; however, the underlying mechanism commonly involves one of:

- Platelet disorders (thrombocytopenic purpura)

- Primary thrombocytopenic purpura

- Secondary thrombocytopenic purpura

- Post-transfusion purpura

- Vascular disorders (nonthrombocytopenic purpura)

- Microvascular injury, as seen in senile (old age) purpura, when blood vessels are more easily damaged

- Hypertensive states

- Deficient vascular support

- Vasculitis, as in the case of Henoch–Schönlein purpura

- Coagulation disorders

- Disseminated intravascular coagulation (DIC)

- Scurvy (vitamin C deficiency) - defect in collagen synthesis due to lack of hydroxylation of procollagen results in weakened capillary walls and cells

- Meningococcemia

- Cocaine use with concomitant use of the one-time chemotherapy drug and now veterinary deworming agent levamisole can cause purpura of the ears, face, trunk, or extremities, sometimes needing reconstructive surgery. Levamisole is purportedly a common cutting agent.

- Decomposition of blood vessels including purpura is a symptom of acute radiation poisoning in excess of 2 Grays of radiation exposure. This is an uncommon cause in general, but is commonly seen in victims of nuclear disaster.

Cases of psychogenic purpura are also described in the medical literature, some claimed to be due to "autoerythrocyte sensitization". Other studies suggest the local (cutaneous) activity of tissue plasminogen activator can be increased in psychogenic purpura, leading to substantial amounts of localized plasmin activity, rapid degradation of fibrin clots, and resultant bleeding. Petechial rash is also characteristic of a rickettsial infection.

HELLP syndrome is a life-threatening pregnancy complication usually considered to be a variant or complication of pre-eclampsia. Both conditions usually occur during the later stages of pregnancy, or sometimes after childbirth. "HELLP" is an abbreviation of the three main features of the syndrome: Hemolysis, Elevated Liver enzymes, and Low Platelet count. The syndrome may be associated with serious liver manifestations, including death of liver cells due to inadequate blood flow and oxygen delivery, bleeding, and rupture.