The Spleen Isn't Optional, Just Resilient

The spleen sits under the left rib cage, about the size of a fist, weighing around 150 grams in a healthy adult. It filters blood. Specifically, it filters old red blood cells — the spleen is where about a third of aging erythrocytes are phagocytosed and recycled — and it's a major site where the immune system encounters bloodborne pathogens for the first time. Its marginal zone holds a distinctive population of B cells that respond to polysaccharide antigens: the capsule sugars on Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitidis.

Surgeons have been removing spleens since the 19th century, often after blunt abdominal trauma, hematologic disease, or cancer. In most cases the patient lives. What followed for decades was the assumption that splenectomy was a minor organ loss. Starting in the 1960s, pediatricians noticed a specific and terrifying complication: overwhelming post-splenectomy infection (OPSI). It comes on fast — fever, chills, hypotension, death within 24–48 hours — and carries a mortality around 50% even with modern ICU care.

The lifetime OPSI risk in asplenic patients is estimated between 0.1% and 0.5% per year, with a case fatality rate near 50%. That works out to roughly 50 times the baseline risk in the general population. The specific culprits are the encapsulated bacteria — pneumococcus is the most common, accounting for perhaps 60% of cases. Standard of care now is a stack of vaccines (pneumococcal, meningococcal, Hib) before elective splenectomy and daily antibiotic prophylaxis for at least the first few years after.

Splenic function is not fully replaced by the liver and lymph nodes. It is a specific organ with a specific job filtering encapsulated bacteria from the blood, and when you remove it, the person is measurably more fragile for the rest of their life. A spleen's value is an insurance policy — most people never cash out, some people die for the lack of one.