Purpura fulminans is rare and most commonly occurs in babies and small children but can also be a rare manifestation in adults when it is associated with severe infections. For example, Meningococcal septicaemia is complicated by purpura fulminans in 10–20% of cases among children. Purpura fulminans associated with congenital (inherited) protein C deficiency occurs in 1:500,000–1,000,000 live births.

The amount of fresh frozen plasma required to reverse disseminated intravascular coagulation associated with purpura fulminans may lead to complications of fluid overload and death, especially in neonates, such as transfusion-related acute lung injury. Exposure to multiple plasma donors over time increases the cumulative risk for transfusion-associated viral infection and allergic reaction to donor proteins found in fresh frozen plasma.

Allergic reactions and alloantibody formation are also potential complications, as with any protein replacement therapy.

Concomitant warfarin therapy in subjects with congenital protein C deficiency is associated with an increased risk of warfarin skin necrosis.

Prognosis varies depending on the underlying disorder, and the extent of the intravascular thrombosis (clotting). The prognosis for those with DIC, regardless of cause, is often grim: Between 20% and 50% of patients will die. DIC with sepsis (infection) has a significantly higher rate of death than DIC associated with trauma.

There are autoimmune causes of coagulation disorders. They include acquired antibodies to coagulation factors, termed inhibitors of coagulation. The main inhibitor is directed against clotting Factor VIII. Another example is antiphospholipid syndrome an autoimmune, hypercoagulable state.

DIC is observed in approximately 1% of academic hospital admissions. DIC occurs at higher rates in people with bacterial sepsis (83%), severe trauma (31%), and cancer (6.8%).

Acquired causes of coagulopathy include anticoagulation with warfarin, liver failure, Vitamin K deficiency and disseminated intravascular coagulation.Additionally, the haemotoxic venom from certain species of snakes can cause this condition, for example Bothrops, rattlesnakes and other species of viper. Viral hemorrhagic fevers include dengue hemorrhagic fever and Dengue Shock Syndrome

Leukemia may also cause coagulopathy. Furthermore, cystic fibrosis has been known to cause bleeding diathesis, especially in undiagnosed infants, due to malabsorption of fat soluble vitamins like Vitamin K.

Secondary TTP is diagnosed when the patient's history mentions one of the known features associated with TTP. It comprises about 40% of all cases of TTP. Predisposing factors are:

- Cancer

- Bone marrow transplantation

- Pregnancy

- Medication use:

- Antiviral drugs (acyclovir)

- Certain chemotherapy medications such as gemcitabine and mitomycin C

- Quinine

- Oxymorphone

- Quetiapine

- Bevacizumab

- Sunitinib

- Platelet aggregation inhibitors (ticlopidine, clopidogrel, and prasugrel)

- Immunosuppressants (ciclosporin, mitomycin, tacrolimus/FK506, interferon-α)

- Hormone altering drugs (estrogens, contraceptives, hormone replacement therapy)

- HIV-1 infection

The mechanism of secondary TTP is poorly understood, as ADAMTS13 activity is generally not as depressed as in idiopathic TTP, and inhibitors cannot be detected. Probable etiology may involve, at least in some cases, endothelial damage, although the formation of thrombi resulting in vessel occlusion may not be essential in the pathogenesis of secondary TTP. These factors may also be considered a form of secondary aHUS; patients presenting with these features are, therefore, potential candidates for anticomplement therapy.

The mortality rate is around 95% for untreated cases, but the prognosis is reasonably favorable (80–90% survival) for patients with idiopathic TTP diagnosed and treated early with plasmapheresis.

Studies have found that about 5 percent of Caucasians in North America have factor V Leiden. The condition is less common in Latin Americans and African-Americans and is extremely rare in people of Asian descent.

Up to 30 percent of patients who present with deep vein thrombosis (DVT) or pulmonary embolism have this condition. The risk of developing a clot in a blood vessel depends on whether a person inherits one or two copies of the factor V Leiden mutation. Inheriting one copy of the mutation from a parent (heterozygous) increases by fourfold to eightfold the chance of developing a clot. People who inherit two copies of the mutation (homozygous), one from each parent, may have up to 80 times the usual risk of developing this type of blood clot. Considering that the risk of developing an abnormal blood clot averages about 1 in 1,000 per year in the general population, the presence of one copy of the factor V Leiden mutation increases that risk to between 4 in 1,000 to 8 in 1,000. Having two copies of the mutation may raise the risk as high as 80 in 1,000. It is unclear whether these individuals are at increased risk for "recurrent" venous thrombosis. While only 1 percent of people with factor V Leiden have two copies of the defective gene, these homozygous individuals have a more severe clinical condition. The presence of acquired risk factors for venous thrombosis—including smoking, use of estrogen-containing (combined) forms of hormonal contraception, and recent surgery—further increase the chance that an individual with the factor V Leiden mutation will develop DVT.

Women with factor V Leiden have a substantially increased risk of clotting in pregnancy (and on estrogen-containing birth control pills or hormone replacement) in the form of deep vein thrombosis and pulmonary embolism. They also may have a small increased risk of preeclampsia, may have a small increased risk of low birth weight babies, may have a small increased risk of miscarriage and stillbirth due to either clotting in the placenta, umbilical cord, or the fetus (fetal clotting may depend on whether the baby has inherited the gene) or influences the clotting system may have on placental development. Note that many of these women go through one or more pregnancies with no difficulties, while others may repeatedly have pregnancy complications, and still others may develop clots within weeks of becoming pregnant.

The normal clotting process depends on the interplay of various proteins in the blood. Coagulopathy may be caused by reduced levels or absence of blood-clotting proteins, known as clotting factors or coagulation factors. Genetic disorders, such as hemophilia and Von Willebrand's disease, can cause a reduction in clotting factors.

Anticoagulants such as warfarin will also prevent clots from forming properly. Coagulopathy may also occur as a result of dysfunction or reduced levels of platelets (small disk-shaped bodies in the bloodstream that aid in the clotting process).

Warfarin necrosis usually occurs three to five days after drug therapy is begun, and a high initial dose increases the risk of its development. Heparin-induced necrosis can develop both at sites of local injection and - when infused intravenously - in a widespread pattern.

In warfarin's initial stages of action, inhibition of protein C and Factor VII is stronger than inhibition of the other vitamin K-dependent coagulation factors II, IX and X. This results from the fact that these proteins have different half-lives: 1.5 to six hours for factor VII and eight hours for protein C, versus one day for factor IX, two days for factor X and two to five days for factor II. The larger the initial dose of vitamin K-antagonist, the more pronounced these differences are. This coagulation factor imbalance leads to paradoxical activation of coagulation, resulting in a hypercoagulable state and thrombosis. The blood clots interrupt the blood supply to the skin, causing necrosis. Protein C is an innate anticoagulant, and as warfarin further decreases protein C levels, it can lead to massive thrombosis with necrosis and gangrene of limbs.

Notably, the prothrombin time (or international normalized ratio, INR) used to test the effect of warfarin is highly dependent on factor VII, which explains why patients can have a therapeutic INR (indicating good anticoagulant effect) but still be in a hypercoagulable state.

In one third of cases, warfarin necrosis occurs in patients with an underlying, innate and previously unknown deficiency of protein C. The condition is related to purpura fulminans, a complication in infants with sepsis (blood stream infection) which also involves skin necrosis. These infants often have protein C deficiency as well. There have also been cases in patients with other deficiency, including protein S deficiency, activated protein C resistance (Factor V Leiden) and antithrombin III deficiency.

Although the above theory is the most commonly accepted theory, others believe that it is a hypersensitivity reaction or a direct toxic effect.

Like most aspects of the disorder, life expectancy varies with severity and adequate treatment. People with severe haemophilia who don't receive adequate, modern treatment have greatly shortened lifespans and often do not reach maturity. Prior to the 1960s when effective treatment became available, average life expectancy was only 11 years. By the 1980s the life span of the average haemophiliac receiving appropriate treatment was 50–60 years. Today with appropriate treatment, males with haemophilia typically have a near normal quality of life with an average lifespan approximately 10 years shorter than an unaffected male.

Since the 1980s the primary leading cause of death of people with severe haemophilia has shifted from haemorrhage to HIV/AIDS acquired through treatment with contaminated blood products. The second leading cause of death related to severe haemophilia complications is intracranial haemorrhage which today accounts for one third of all deaths of people with haemophilia. Two other major causes of death include hepatitis infections causing cirrhosis and obstruction of air or blood flow due to soft tissue haemorrhage.

Treatment of asymptomatic congenital dysfibrinogenemia depends in part on the expectations of developing bleeding and/or thrombotic complications as estimated based on the history of family members with the disorder and, where available, determination of the exact mutation causing the disorder plus the propensity of the particular mutation type to develop these complications. In general, individuals with this disorder require regular follow-up and multidiscipline management prior to surgery, pregnancy, and giving childbirth. Women with the disorder appear to have an increased rate of miscarriages and all individuals with fibrinogen activity in clotting tests below 0.5 grams/liter are prone to bleeding and spontaneous abortions. Women with multiple miscarriages and individuals with excessively low fibrinogen activity levels should be considered for prophylaxis therapy with fibrinogen replacement during pregnancy, delivery, and/or surgery.

Individuals experiencing episodic bleeding as a result of congenital dysfibrinogenemia should be treated at a center specialized in treating hemophilia. They should avoid all medications that interfere with normal platelet function. During bleeding episodes, treatment with fibrinogen concentrates or in emergencies or when these concentrates are unavailable, infusions of fresh frozen plasma and/or cryoprecipitate (a fibrinogen-rich plasma fraction) to maintain fibrinogen activity levels >1 gram/liter. Tranexamic acid or fibrinogen concentrates are recommended for prophylactic treatment prior to minor surgery while fibrinogen concentrates are recommended prior to major surgery with fibrinogen concentrates usage seeking to maintain fibrinogen activity levels at >1 gram/liter. Women undergoing vaginal or Cesarean child birth should be treated at a hemophilia center with fibrinogen concentrates to maintain fibrinogen activity levels at 1.5 gram/liter. The latter individuals require careful observation for bleeding during their post-partum periods.

Individuals experiencing episodic thrombosis as a result of congenital dysfibrinogenemia should also be treated at a center specialized in treating hemophilia using antithrombotic agents. They should be instructed on antithrombotic behavioral methods fur use in high risk situations such as long car rides and air flights. Venous thrombosis should be treated with low molecular weight heparin for a period that depends on personal and family history of thrombosis events. Prophylactic treatment prior to minor surgery should avoid fibrinogen supplementation and use prophylactic anticoagulation measures; prior to major surgery, fibrinogen supplementation should be used only if serious bleeding occurs; otherwise, prophylactic anticoagulation measures are recommended.

aHUS can be inherited or acquired, and does not appear to vary by race, gender, or geographic area. As expected with an ultra-rare disease, data on the prevalence of aHUS are extremely limited. A pediatric prevalence of 3.3 cases per million population is documented in one publication of a European hemolytic uremic syndrome (HUS) registry involving 167 pediatric patients.

If someone has coagulopathy, their health care provider may help them manage their symptoms with medications or replacement therapy. In replacement therapy, the reduced or absent clotting factors are replaced with proteins derived from human blood or created in the laboratory. This therapy may be given either to treat bleeding that has already begun or to prevent bleeding from occurring.

Haemophilia is rare, with only about 1 instance in every 10,000 births (or 1 in 5,000 male births) for haemophilia A and 1 in 50,000 births for haemophilia B. About 18,000 people in the United States have haemophilia. Each year in the US, about 400 babies are born with the disorder. Haemophilia usually occurs in males and less often in females. It is estimated that about 2500 Canadians have haemophilia A, and about 500 Canadians have haemophilia B.

Thrombocytopenia affects a few percent of newborns, and its prevalence in neonatal intensive care units (NICU) is high. Normally, it is mild and resolves without consequences. Most cases affect preterm birth infants and result from placental insufficiency and/or fetal hypoxia. Other causes, such as alloimmunity, genetics, autoimmunity, and infection, are less frequent.

Thrombocytopenia that starts after the first 72 hours since birth is often the result of underlying sepsis or necrotizing enterocolitis (NEC). In the case of infection, PCR tests may be useful for rapid pathogen identification and detection of antibiotic resistance genes. Possible pathogens include viruses (e.g. Cytomegalovirus (CMV), rubella virus, HIV), bacteria (e.g. "Staphylococcus sp.", "Enterococcus sp.", "Streptococcus agalactiae" (GBS), "Listeria monocytogenes", "Escherichia coli", "Haemophilus influenzae", "Klebsiella pneumoniae", "Pseudomonas aeruginosa", "Yersinia enterocolitica"), fungi (e.g. "Candida sp."), and "Toxoplasma gondii". The severity of thrombocytopenia may be correlated with pathogen type; some research indicates that the most severe cases are related to fungal or gram-negative bacterial infection. The pathogen may be transmitted during or before birth, by breast feeding, or during transfusion. Interleukin-11 is being investigated as a drug for managing thrombocytopenia, especially in cases of sepsis or necrotizing enterocolitis (NEC).

Many conditions mimic or may be mistaken for warfarin necrosis, including pyoderma gangrenosum or necrotizing fasciitis. Warfarin necrosis is also different from another drug eruption associated with warfarin, purple toe syndrome, which usually occurs three to eight weeks after the start of anticoagulation therapy. No report has described this disorder in the immediate postpartum period in patients with protein S deficiency.

Patients with aHUS have an extremely poor prognosis. Among those with the most commonly identified aHUS genetic mutation, the proportion of patients experiencing negative outcomes (e.g., need for dialysis, permanent kidney damage, death) within the first year rises to 70%. However, sudden morbidity and mortality can occur regardless of mutational status. aHUS can arise at any age, with more than 40% of cases first reported after 18 years of age. The oldest presentation in one study was at age 83. As noted above, kidney transplantation for aHUS patients with ESRD was rarely considered because of a high incidence of graft loss due to TMA recurrence in the transplanted organ in up to 90% of patients. Consequently, most aHUS patients with ESRD undergo chronic dialysis, which is associated with significant morbidities and worsened prognosis. Combined liver-kidney transplantation has been attempted in patients with aHUS, although this high-risk procedure has a mortality rate approaching 50%.

Quality of life is very poor for patients with aHUS, who are burdened with fatigue, renal complications, hypertension, neurological impairment, gastrointestinal distress, clotting at the site of venous access, and ultimately, death. PE/PI is also reported to be associated with significant safety risks and is highly disruptive to patients’ lives due to the requirements for extensive vascular access and frequent administration.

While the prognosis of cryofibrinoginemic disease varies greatly depending on its severity as well as the severity of its associated disorders, satisfactory clinical outcomes are reported in 50-80% of patients with primary or secondary disease treated with corticosteroid and/or immunosuppressive regimens. However, relapses occur within the first 6 months after stopping or decreasing therapy in 40-76% of cases. Sepsis resulting from infection of necrotic tissue is the most common threat to life in primary disease whereas the associated disorder is a critical determinant of prognosis in secondary disease.

The following medications can induce thrombocytopenia through direct myelosuppression.

- Valproic acid

- Methotrexate

- Carboplatin

- Interferon

- Isotretinoin

- Panobinostat

- H blockers and proton-pump inhibitors

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.

Thrombocytopenic purpura are purpura associated with a reduction in circulating blood platelets which can result from a variety of causes, such as kaposi sarcoma.

The occurrence of cryofibrinogenemia as defined by a 4 °C-induced formation of fibrinogen-based precipitation in plasma occurs in 2% to 9% of asymptomatic individuals and 8% to 13% of hospitalized patients without symptoms attributable to this precipitation. Most of these cases have relatively low levels of cold temperature-induced fibrinogen precipitate levels (<50 milligram/liter of fibrinogen) and do not have a disorder associated with the development of cryofibrinogenmia.