Plasma donation involves drawing blood, separating the pale-yellow plasma component, and returning the remaining cellular components to the donor. This procedure removes fluid from the body, immediately impacting the circulatory system. Consequently, plasma donation causes a temporary, measurable drop in blood pressure. However, this effect is transient and should not be considered a treatment for chronic high blood pressure (hypertension).
The Immediate Physiological Impact of Plasma Donation
The acute change in blood pressure is primarily due to the rapid, temporary decrease in total blood volume, caused by the removal of plasma, which is largely water. A typical plasma donation removes approximately 625 to 800 milliliters of plasma, a substantial portion of the body’s circulating fluid. This sudden volume loss reduces the pressure exerted on arterial walls, leading to an immediate, short-lived drop in blood pressure.
The body counteracts this sudden fluid loss to maintain circulatory stability. Moments after plasma removal, the baroreceptor reflex activates, sensing the pressure drop and signaling the heart to beat faster and blood vessels to constrict. Fluid also shifts rapidly from interstitial spaces into the blood vessels to restore plasma volume. This rapid compensation ensures the blood pressure drop is usually minimal and quickly reversed in healthy individuals. Some donors may experience mild symptoms associated with this acute drop, such as lightheadedness or dizziness.
Blood Pressure Screening for Donors
To protect donor safety regarding the acute volume shift, every plasma donor undergoes a mandatory health screening before each donation, which includes a blood pressure check. This screening ensures the donor’s cardiovascular system can handle the temporary reduction in blood volume. Regulatory bodies have established specific acceptable ranges for blood pressure that a donor must meet to proceed.
Acceptable systolic blood pressure typically ranges between 90 and 180 millimeters of mercury (mmHg), and diastolic pressure must generally be between 50 and 100 mmHg. A reading outside these parameters often results in a temporary deferral of the donation. Individuals managing pre-existing hypertension with medication can still be eligible, provided their blood pressure is within the safe, controlled range on the day of donation. Screening minimizes the risk of a hypotensive reaction, where the temporary drop becomes too severe.
Long-Term Effects on Chronic Blood Pressure
Plasma donation is not a substitute for prescribed medical treatment, as the body’s homeostatic systems restore lost fluid and components quickly. The fluid volume lost is typically replenished within 24 to 48 hours through fluid intake and renal adjustments. Proteins and other components removed are regenerated by the liver over days to a few weeks, negating any sustained impact from a single donation.
Some studies have explored the effect of frequent, regular plasma donations on individuals with pre-existing high blood pressure. These analyses suggest that frequent donation (at intervals less than 14 days) may lead to a modest, sustained reduction in both systolic and diastolic blood pressure for donors with Stage 1 or Stage 2 hypertension. This effect is not observed in individuals with normal blood pressure. The sustained reduction is hypothesized to be due to the regular removal of certain circulating molecules or blood pressure-active substances found in the plasma, rather than temporary fluid loss. Despite these findings, this effect is specific to frequent donors with hypertension and should not be relied upon as a primary medical therapy.