Anti-platelet autoantibodies in a pregnant woman with ITP will attack the patient's own platelets and will also cross the placenta and react against fetal platelets. Therefore, ITP is a significant cause of fetal and neonatal immune thrombocytopenia. Approximately 10% of newborns affected by ITP will have platelet counts <50,000/uL and 1% to 2% will have a risk of intracerebral hemorrhage comparable to infants with neonatal alloimmune thrombocytopenia (NAIT).

No lab test can reliably predict if neonatal thrombocytopenia will occur. The risk of neonatal thrombocytopenia is increased with:

- Mothers with a history of splenectomy for ITP

- Mothers who had a previous infant affected with ITP

- Gestational (maternal) platelet count less than 100,000/uL

It is recommended that pregnant women with thrombocytopenia or a previous diagnosis of ITP should be tested for serum antiplatelet antibodies. A woman with symptomatic thrombocytopenia and an identifiable antiplatelet antibody should be started on therapy for their ITP which may include steroids or IVIG. Fetal blood analysis to determine the platelet count is not generally performed as ITP-induced thrombocytopenia in the fetus is generally less severe than NAIT. Platelet transfusions may be performed in newborns, depending on the degree of thrombocytopenia. It is recommended that neonates be followed with serial platelet counts for the first few days after birth.,

A normal platelet count is considered to be in the range of 150,000–450,000 per microlitre (μl) of blood for most healthy individuals. Hence one may be considered thrombocytopenic below that range, although the threshold for a diagnosis of ITP is not tied to any specific number.

The incidence of ITP is estimated at 50–100 new cases per million per year, with children accounting for half of that amount. At least 70 percent of childhood cases will end up in remission within six months, even without treatment. Moreover, a third of the remaining chronic cases will usually remit during follow-up observation, and another third will end up with only mild thrombocytopenia (defined as a platelet count above 50,000). A number of immune related genes and polymorphisms have been identified as influencing predisposition to ITP, with FCGR3a-V158 allele and KIRDS2/DL2 increasing susceptibility and KIR2DS5 shown to be protective.

ITP is usually chronic in adults and the probability of durable remission is 20–40 percent. The male to female ratio in the adult group varies from 1:1.2 to 1.7 in most age ranges (childhood cases are roughly equal for both genders) and the median age of adults at the diagnosis is 56–60. The ratio between male and female adult cases tends to widen with age. In the United States, the adult chronic population is thought to be approximately 60,000—with women outnumbering men approximately 2 to 1, which has resulted in ITP being designated an orphan disease.

The mortality rate due to chronic ITP varies but tends to be higher relative to the general population for any age range. In a study conducted in Great Britain, it was noted that ITP causes an approximately 60 percent higher rate of mortality compared to gender- and age-matched subjects without ITP. This increased risk of death with ITP is largely concentrated in the middle-aged and elderly. Ninety-six percent of reported ITP-related deaths were individuals 45 years or older. No significant difference was noted in the rate of survival between males and females.

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.

By tradition, the term idiopathic thrombocytopenic purpura is used when the cause is idiopathic. However, most cases are now considered to be immune-mediated.

Another form is thrombotic thrombocytopenic purpura.

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).

Diagnosis is done by the help of symptoms and only blood count abnormality is thrombocytopenia.

Purpura is a condition of red or purple discolored spots on the skin that do not blanch on applying pressure. The spots are caused by bleeding underneath the skin usually secondary to vasculitis or dietary deficiency of vitamin C (scurvy). They measure 0.3–1 cm (3–10 mm), whereas petechiae measure less than 3 mm, and ecchymoses greater than 1 cm.

Purpura is common with typhus and can be present with meningitis caused by meningococci or septicaemia. In particular, meningococcus ("Neisseria meningitidis"), a Gram-negative diplococcus organism, releases endotoxin when it lyses. Endotoxin activates the Hageman factor (clotting factor XII), which causes disseminated intravascular coagulation (DIC). The DIC is what appears as a rash on the affected individual.

Drug-induced purpura is a skin condition that may be related to platelet destruction, vessel fragility, interference with platelet function, or vasculitis.

Nonthrombocytopenic purpura is a type of purpura (red or purple skin discoloration) not associated with thrombocytopenia.

Examples/causes include:

- Henoch–Schönlein purpura.

- Hereditary hemorrhagic telangiectasia

- Congenital cytomegalovirus

- Meningococcemia

Abnormally high rates of platelet destruction may be due to immune or non-immune conditions, including:

- Immune thrombocytopenic purpura

- Thrombotic thrombocytopenic purpura

- Hemolytic-uremic syndrome

- Disseminated intravascular coagulation

- Paroxysmal nocturnal hemoglobinuria

- Antiphospholipid syndrome

- Systemic lupus erythematosus

- Post-transfusion purpura

- Neonatal alloimmune thrombocytopenia

- Hypersplenism

- Dengue fever

- Gaucher's disease

- Zika virus

Overall prognosis is good in most patients, with one study showing recovery occurring in 94% and 89% of children and adults, respectively (some having needed treatment). In children under ten, the condition recurs in about a third of all cases and usually within the first four months after the initial attack. Recurrence is more common in older children and adults.

Amyloid purpura affects a minority of individuals with amyloidosis. For example, purpura is present early in the disease in approximately 15% of patients with primary systemic amyloidosis.

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.

Purpura fulminans is caused by defects in the protein C anticoagulant pathway. Identification of the cause of purpura fulminans often depends on the patient’s age and circumstances of presentation.

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.

In adults, kidney involvement progresses to end-stage renal disease (ESRD) more often than in children. In a UK series of 37 patients, 10 (27%) developed advanced kidney disease. Proteinuria, hypertension at presentation, and pathology features (crescentic changes, interstitial fibrosis and tubular atrophy) predicted progression. About 20% of children that exhibit nephrotic or nephritic features experience long permanent renal impairment.

The findings on renal biopsy correlate with the severity of symptoms: those with asymptomatic hematuria may only have focal mesangial proliferation while those with proteinuria may have marked cellular proliferation or even crescent formation. The number of crescentic glomeruli is an important prognostic factor in determining whether the patient will develop chronic renal disease.

In ESRD, some eventually need hemodialysis or equivalent renal replacement therapy (RRT). If a kidney transplant is found for a patient on RRT, the disease will recur in the graft (transplanted kidney) in about 35% of cases, and in 11%, the graft will fail completely (requiring resumption of the RRT and a further transplant).

The precise cause of amyloid purpura is unknown, but several mechanisms are thought to contribute. One may be a decrease in the level of circulating factor X, a clotting factor necessary for coagulation. The proposed mechanism for this decrease in factor X is that circulating amyloid fibrils bind and inactivate factor X. Another contributing factor may be enhanced fibrinolysis, the breakdown of clots. Subendothelial deposits of amyloid may weaken blood vessels and lead to the extravasation of blood. Amyloid deposits in the gastrointestinal tract and liver may also play a role in the development of amyloid purpura.

Cryoglobulonemia may occur without evidence of an underlying associated disorders, i.e. primary cryoglobulinemia (also termed essential cryoglobulinemia) or, far more commonly, with evidence of an underlying disease, i.e. secondary cryoglobulonemia. Secondary cryofibrinoenemia can develop in individuals suffering infection (~12% of cases), malignant or premalignant disorders (21%), vasculitis (25%), and autoimmune diseases (42%). In these cases of the secondary disorder, cryofibinogenema may or may not cause tissue injury and/or other symptoms and the actual cause-effect relationship between these diseases and the development of cryofibrinogenmia is unclear. Cryofibrinogenemia can also occur in association with the intake of certain drugs.

Evans syndrome is rare, serious, and has a reported mortality rate of 7%.

It has been observed that there is a risk of developing other autoimmune problems and hypogammaglobulinemia, with recent research finding that 58% of children with Evans syndrome have CD4-/CD8- T cells which is a strong predictor for having autoimmune lymphoproliferative syndrome.

Drug-induced thrombocytopenic purpura is a skin condition result from a low platelet count due to drug-induced anti-platelet antibodies caused by drugs such as heparin, sulfonamines, digoxin, quinine, and quinidine.

Considered a rare to very rare autoimmune disorder it has had few studies with cohorts often less than 30.

Acquired hemolytic anemia can be divided into immune and non-immune mediated forms of hemolytic anemia.

Waldenström hyperglobulinemic purpura (also known as "Purpura hyperglobulinemica") is a skin condition that presents with episodic showers of petechiae (small red or purple spots) occurring on all parts of the body, most profusely on the lower extremities.

Vasculitis secondary to connective tissue disorders. Usually secondary to systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), relapsing polychondritis, Behçet's disease, and other connective tissue disorders.

Vasculitis secondary to viral infection. Usually due to hepatitis B and C, HIV, cytomegalovirus, Epstein-Barr virus, and Parvo B19 virus.

The specific cause is dependent of the type of TMA that is presented, but the two main pathways that lead to TMA are external triggers of vascular injury, such as viruses, bacterial Shiga toxins or endotoxins, antibodies, and drugs; and congenital predisposing conditions, including decreased levels of tissue factors necessary for the coagulation cascade. Either of these pathways will result in decreased endothelial thromboresistance, leukocyte adhesion to damaged endothelium, complement consumption, enhanced vascular shear stress, and abnormal vWF fragmentation. The central and primary event in this progression is injury to the endothelial cells, which reduces the production of prostaglandin and prostacyclin, ultimately resulting in the loss of physiological thromboresistance, or high thrombus formation rate in blood vessels. Leukocyte adhesion to the damaged endothelial wall and abnormal von Willebrand factor (or vWF) release can also contribute to the increase in thrombus formation. More recently, researchers have attributed both TTP and HUS to targeted agents, such as targeted cancer therapies, immunotoxins, and anti-VEGF therapy.

Bacterial toxins are the primary cause of one category of thrombotic microangiopathy known as HUS or hemolytic uremic syndrome. HUS can be divided into two main categories: Shiga-toxin-associated HUS (STx-HUS), which normally presents with diarrhea, and atypical HUS. The Shiga-toxin inhibits the binding of eEF-1-dependent binding of aminoacyl tRNA to the 60S subunit of the ribosome, thus inhibiting protein synthesis. The cytotoxicity from the lack of protein damages glomerular endothelial cells by creating voids in the endothelial wall and detaching the basement membrane of the endothelial layer, activating the coagulation cascade. Atypical HUS may be caused by an infection or diarrheal illness or it may be genetically transmitted. This category of TMA encompasses all forms that do not have obvious etiologies. Mutations in three of the proteins in the complement cascade have been identified in patients with atypical HUS. Several chemotherapeutic drugs have also been shown to cause damage to the epithelial layer by reducing the ability for the cells to produce prostacyclin, ultimately resulting in chemotherapy-associated HUS, or C-HUS.

The second category of TMAs is TTP thrombotic thrombocytopenic purpura, which can be divided into 3 categories: congenital, idiopathic, and non-idiopathic. Congenital and idiopathic TTP are generally associated with deficiencies in ADAMTS13, a zinc metalloprotease responsible for cleaving Very Large vWF Multimers in order to prevent inappropriate platelet aggregation and thrombosis in the microvasculature. Natural genetic mutations resulting in the deficiency of ADAMTS13 have been found in homozygous and heterozygous pedigrees in Europe. Researchers have identified common pathways and links between TTP and HUS, while other sources express skepticism about their common pathophysiology.

The repression of the vascular endothelial growth factor (VEGF) can also cause glomerular TMA (damage to the glomerular microvasculature). It is likely that the absence of VEGF results in the collapse of fenestrations in the glomerular endothelium, thus causing microvascular injury and blockages associated with TMA.

Manifestations resembling thrombotic microangiopathy have been reported in clinical trials evaluating high doses of Valacyclovir (8000 mg/day) administered for prolonged periods (months to years) for prophylaxis of cytomegalovirus (CMV) infection and disease, particularly in persons with HIV infection. A number of factors may have contributed to the incidence of thrombotic microangiopathy in those trials including profound immunosuppression, underlying diseases (advanced HIV disease, graft-versus-host disease), and other classes of drug, particularly antifungal agents. There were no reports of thrombotic microangiopathy among the 3050 subjects in the four trials evaluating Valacyclovir for suppression of recurrent genital herpes. Although one of the trials was in HIV-infected subjects, the patients did not have advanced HIV disease. The implication is that the occurrence of thrombotic microangiopathy is restricted to severely immunosuppressed persons receiving higher Valacyclovir dosages than are required to control HSV infection.