Immune Thrombocytopenia (ITP) is an acquired autoimmune disorder characterized by an isolated low platelet count, specifically fewer than 100,000 platelets per microliter of blood. This occurs because the immune system mistakenly attacks and destroys the body’s own platelets, which are necessary for normal clotting. Understanding the number of people affected requires examining statistical measures like incidence and prevalence across different population groups.
Overall Incidence and Prevalence Rates
The occurrence of ITP is measured by incidence (new cases diagnosed per year) and prevalence (total individuals living with the condition). Global estimates suggest the annual incidence of ITP across all ages falls within a range of approximately 2 to 5 new cases per 100,000 people. However, recent data from some national studies, particularly in the United States, indicate a higher annual incidence rate, closer to 6.1 cases per 100,000 persons.
ITP is considered a relatively rare disorder. For adults, the annual incidence is often cited between 1 and 6 cases per 100,000 individuals. Because ITP tends to become a long-term condition in adults, the overall prevalence is significantly higher than the incidence. The total prevalence in the adult population is estimated to be around 12 cases per 100,000 people.
How ITP Rates Differ Between Children and Adults
ITP rates differ significantly across age groups. ITP exhibits a bimodal distribution, meaning incidence rates peak at two points: childhood and older adulthood. The highest reported incidence rates in the US are found in the youngest age group, children aged 0 to 4 years, where the rate can reach 8.1 new cases per 100,000 individuals annually.
The overall incidence of ITP in children is estimated to be between 1.9 and 6.4 cases per 100,000 children per year. The lowest rates are found in the 5 to 17-year-old age group, at approximately 3.6 per 100,000. Incidence begins to climb again in middle age, peaking in the elderly population. Adults aged 65 years and older experience the highest rate of all, at 13.7 new cases per 100,000 people.
Childhood ITP affects males and females nearly equally, although a higher male-to-female ratio is sometimes observed in infancy. In adults, the overall incidence is often slightly higher in females, and this difference becomes more pronounced in younger adults and adolescents. The disease course and need for ongoing treatment vary significantly between the two age groups. The differing rates reflect distinctions in the disease’s triggers, which often involve viral infections in children compared to chronic factors in adults.
Statistical Breakdown of Acute Versus Chronic Cases
The clinical course of ITP is categorized by the duration of the low platelet count. Standard international terminology divides the disease into three phases based on the time since diagnosis. “Newly diagnosed” ITP refers to the condition during the first three months. If the low platelet count persists between three and 12 months, the condition is classified as “persistent ITP.”
The condition is termed “chronic ITP” if it lasts for more than 12 months. This distinction highlights a major difference between the pediatric and adult forms of the disorder. In children, ITP is predominantly an acute and self-limiting disease, often resolving spontaneously within six months for approximately 70% to 85% of cases.
A significant minority of pediatric patients, approximately 20% to 25%, do not experience spontaneous remission and progress to chronic ITP. In the adult population, progression to chronicity is the expected outcome, as spontaneous remission is uncommon. The majority of adult patients require ongoing treatment and management, meaning chronic cases account for the bulk of the adult prevalence.