Blood Donation Eligibility Calculator

Introduction to donor screening arithmetic in United States blood banking

Every blood collection in the United States begins with the same short list of measurable quantities: how old the donor is, how much the donor weighs, how tall the donor is for apheresis products, what the donor's hemoglobin or hematocrit reads at the fingerstick, how many days have passed since the last collection of that component, and how many collections of that component have already happened in the rolling year. Those numbers are not folklore. They are written into Title 21 of the Code of Federal Regulations, into the AABB Standards for Blood Banks and Transfusion Services, and into the published donation-type requirements of collecting organizations such as the American Red Cross.

This calculator reproduces that numeric layer faithfully and shows its working. You select the product you intend to give — whole blood, a double red cell (Power Red) collection, an apheresis platelet collection, or an AB Elite plasma collection — and enter the quantities a screener would measure. The tool then reports, criterion by criterion, which published thresholds you clear and which you do not, estimates your circulating blood volume so you can see how large a standard unit is relative to your own physiology, and compares all four donation types side by side so you can see which product suits you best today.

What the calculator deliberately does not do is decide anything. Donor suitability in the United States rests on three legs: the numeric screen modelled here, a confidential health-history interview built on the AABB Donor History Questionnaire, and laboratory testing of the collected unit. Since May 2023 the interview leg uses individual, risk-based questions asked of every donor rather than population-based deferrals. Medication history, recent travel, tattoos and piercings, pregnancy, recent illness, blood pressure, pulse and temperature can all defer a donor whose arithmetic looks perfect. The collecting center, and only the collecting center, makes the call.

How to use the donor screening tool without misreading it

Work down the form in order. Pick the donation type first, because the age floor, weight floor, height requirement, interval and annual cap all change with the product. Enter your age in whole years as of today. Choose the donor sex the collecting center will use for the hemoglobin threshold; the federal hemoglobin cutoffs and the Red Cross Power Red criteria are written as male and female values, so the tool needs one of the two to pick a threshold.

Enter your weight and switch the adjacent unit control between kilograms and pounds; the value converts as you switch, so nothing is lost. The comparison is then made against the threshold expressed in the unit you chose, which matters more than it sounds: the regulation says 50 kilograms and the Red Cross says 110 pounds, and 110 pounds is 49.9 kilograms, so the two are not identical to the gram. Height is optional for whole blood, platelets and plasma but required for a Power Red evaluation, and supplying it also upgrades the blood-volume estimate from a crude per-kilogram rule to the Nadler regression.

For the blood count, choose whether you are entering a hemoglobin in grams per deciliter or a hematocrit as a percentage, then type the figure from your last fingerstick or laboratory report. Finally, enter the number of days since your last donation of the same component and the number of donations of that component in the past twelve months. Both are optional: leave them blank if you have never donated that product and the tool will say so rather than silently assuming zero.

Press Check eligibility. The result panel announces a verdict, six headline metrics, and a criterion-by-criterion list. Below it, the donation-type comparison panel shows which of the four products your donor characteristics qualify you for and what the published interval and annual cap are for each. Reset restores the defaults, and Download summary saves a plain-text record you can take to the drive.

The screening formulas: thresholds, intervals and blood-volume limits

Hemoglobin and hematocrit thresholds

The hemoglobin rule is a one-sided inequality with a sex-specific floor. Writing for the measured hemoglobin in grams per deciliter and for the regulatory floor, allogeneic donation requires

Formula: H ≥ H_min, H_min = 13.0 male 12.5 female

The equivalent hematocrit floors in 21 CFR 630.10(f)(3)(i) are 39 percent for male donors and 38 percent for female donors. The American Red Cross additionally refuses a donor whose screening hemoglobin reads above 20.0 g/dL, so the practical rule the calculator applies to a hemoglobin entry is the two-sided band

Formula: H_min ≤ H ≤ 20.0

The margin the calculator reports is simply , which tells you how much headroom you have before a normal day-to-day fluctuation of two or three tenths of a gram per deciliter would defer you.

Interval and annual frequency rules

Let be the number of days elapsed since your last collection of the component in question and the published minimum interval. Eligibility requires , and the outstanding wait is the clamped difference

Formula: D_wait = max 0 D_min − D

The federal values are days for whole blood and days when two units of red cells are taken, exactly the 8-week and 16-week figures in 21 CFR 630.15(a)(1)(i). Apheresis platelets carry a 7-day interval and plasma a 28-day interval in Red Cross practice. Annual counts are capped in parallel: if is the number of collections of that component in the trailing twelve months, the requirement is with equal to 6, 3, 24 and 13 for whole blood, Power Red, platelets and plasma respectively.

Blood volume and the collection-fraction limit

The weight floor is not arbitrary; it exists so that one unit stays a small fraction of the donor's circulating volume. When you supply a height the calculator estimates blood volume with the Nadler regression of 1962, in which is height in metres and is weight in kilograms:

Formula: V_blood = 0.3669 h^3 + 0.03219 W + 0.6041 (male, litres)

Formula: V_blood = 0.3561 h^3 + 0.03308 W + 0.1833 (female, litres)

Without a height the tool falls back on the conventional per-kilogram estimate of about 70 mL/kg for men and 65 mL/kg for women and labels the result accordingly. AABB standards cap the total volume drawn, including the test samples, at 10.5 mL per kilogram of donor weight:

Formula: V_max = 10.5 × W mL

and the fraction of your circulating volume that a nominal 500 mL whole blood unit represents is

Formula: f = 500 / (1000 × V_blood) × 100%

The combination of a 110-pound floor and the 10.5 mL/kg cap is designed to keep below roughly 15 percent for every accepted donor, which is why the calculator flags any result above that line even when every hard threshold is met. Unit conversions are exact rather than approximate: and .

Worked example: a repeat whole blood donor at a workplace drive

Take a 34-year-old male donor who weighs 82 kg, stands 180 cm, screened at 15.2 g/dL on the fingerstick, last gave whole blood 70 days ago, and has given whole blood twice in the past twelve months.

Age clears the 16-year floor. Weight clears 50 kg with 32 kg to spare. Hemoglobin clears the 13.0 g/dL male floor with a margin of g/dL and sits well under the 20.0 g/dL ceiling. The interval clears because 70 days exceeds 56, so . Two prior donations leave four of the six permitted collections available in the rolling year.

The blood volume follows from Nadler with m and kg. Since , the estimate is litres. A nominal 500 mL unit is therefore 9.3 percent of his circulating volume, comfortably under the 15 percent design target, and the AABB ceiling on total draw volume is mL. The verdict is that he meets every published numeric criterion for whole blood. The comparison panel additionally shows he qualifies on donor characteristics for Power Red, since 82 kg exceeds the 59 kg male floor and 180 cm exceeds the 155 cm male height requirement, and for platelets and plasma.

Change a single input and the arithmetic bites. Move the last donation to 30 days ago and the interval rule returns days. Drop the hemoglobin to 12.8 g/dL and the male floor defers him even though the same figure would clear the female floor. That asymmetry is real and is the reason the 2015 FDA rule raised the male minimum from 12.5 to 13.0 g/dL: male donors were showing measurable iron depletion at the older threshold.

Interpreting the result and the metrics panel

A green verdict means every published numeric threshold is met for the product you selected. It is a statement about arithmetic, not about health. An amber-style "cannot confirm" verdict appears when a required input is missing, most often a height for a Power Red evaluation, and tells you exactly what to supply. A red verdict lists each failing criterion with the measured value and the threshold side by side so you know whether you are one day short of an interval or twenty kilograms short of a Power Red weight floor.

The metrics deserve individual reading. Estimated blood volume is a population regression, not a measurement, and carries a standard error of several hundred millilitres in individuals. Unit as share of volume is the number that explains the weight floor; if it approaches 15 percent you are a small donor and a vasovagal reaction is more likely, which is why centers push fluids and a salty snack beforehand. Maximum draw volume is the AABB ceiling on what may legally be taken from you including samples. Hemoglobin margin is your buffer against normal biological variation. Days until eligible and donations left this year are planning numbers for the calendar.

One value worth internalising even though it is not an input: a single whole blood donation removes roughly 200 to 250 milligrams of iron. Plasma returns within about a day and red cell mass within weeks, but iron stores take far longer, which is why AABB Association Bulletin #17-02 recommends iron replacement strategies for frequent donors and why the Red Cross suggests continuing supplementation for at least 60 days after a whole blood donation and 120 days after a Power Red donation. A donor who repeatedly clears the hemoglobin screen by a tenth of a gram is a donor whose ferritin is probably falling.

Limitations, assumptions and what this screener cannot see

The most important limitation is scope. This tool models the numeric layer of United States donor screening only. It has no visibility into the health-history questionnaire, which is where the majority of real deferrals originate: recent illness or antibiotics, specific medications such as isotretinoin, finasteride, dutasteride, acitretin or etretinate with their own waiting periods, dental work, tattoos or piercings in unregulated settings, pregnancy within the past six weeks, travel to malaria-endemic regions, a history of certain cancers or cardiac disease, and the individual risk-based questions the FDA finalized in May 2023 concerning new or multiple sexual partners, HIV medication and injection drug use.

It also omits the on-site mini-physical. Under 21 CFR 630.10(f) a donor must present an oral temperature no higher than 37.5 °C (99.5 °F), a systolic blood pressure between 90 and 180 mm Hg, a diastolic pressure between 50 and 100 mm Hg, and a regular pulse between 50 and 100 beats per minute. Those four are measured at the chair, not entered here, and each one defers donors daily.

Several further assumptions are baked in. The thresholds used are those of the United States; Canada, the United Kingdom, Australia, the European Union member states and India all differ, sometimes materially, in minimum age, minimum hemoglobin and inter-donation interval. The age, weight and height criteria for Power Red, platelets and plasma follow American Red Cross published requirements and other collecting organizations may set their own within the federal floor. The interval calculation assumes the days you enter refer to the same component you are now planning to give; cross-component deferrals exist, such as the wait imposed after a double red cell collection before any further red cell loss, and are applied by the center rather than modelled here. The comparison panel evaluates only donor characteristics against each product's age, weight, height and hemoglobin criteria, and reports each product's published interval and annual cap for reference rather than re-testing your interval against all four. The blood volume figure is an estimate from a 1962 regression on healthy adults and should not be used clinically. Finally, the tool accepts a hematocrit entry against the 38 and 39 percent floors but applies the 20.0 g/dL ceiling only to hemoglobin entries, because the published ceiling is expressed in grams per deciliter.

This page is informational and educational. It is not medical advice, it does not create a clinician relationship, and it does not clear anyone to donate. The collecting center performs the screening interview, the mini-physical and the laboratory testing, and the collecting center alone decides whether a donation proceeds.

Frequently asked questions about donor eligibility thresholds

Published criteria by donation type

Sources. U.S. Food and Drug Administration, 21 CFR 630.10, General donor eligibility requirements — weight minimum 50 kg (110 lb), hemoglobin 12.5 g/dL female and 13.0 g/dL male, hematocrit 38 and 39 percent, temperature, blood pressure and pulse limits (eCFR 630.10). U.S. Food and Drug Administration, 21 CFR 630.15, Donation suitability requirements — whole blood no more than once in 8 weeks, two units of red cells no more than once in 16 weeks (eCFR 630.15). U.S. Food and Drug Administration, Recommendations for Evaluating Donor Eligibility Using Individual Risk-Based Questions to Reduce the Risk of Human Immunodeficiency Virus Transmission by Blood and Blood Products; Guidance for Industry, May 2023 (FDA guidance). AABB, Standards for Blood Banks and Transfusion Services and Association Bulletin #17-02, Updated Strategies to Limit or Prevent Iron Deficiency in Blood Donors, plus AABB regulatory guidance on hemoglobin screening and iron management (AABB hemoglobin screening and iron management). American Red Cross, Eligibility Requirements and Requirements by Donation Type — age, weight and height criteria and the 56, 112, 7 and 28-day intervals with annual caps of 6, 3, 24 and 13 (Red Cross eligibility requirements). Nadler SB, Hidalgo JU, Bloch T, Prediction of blood volume in normal human adults, Surgery 1962;51(2):224–232 — the blood-volume regression (PubMed 21936146).