What’s the Probability of a Live Donor Match?

The probability in my case was 100%. It’s amazing that all the pin pricking while Logan was asleep during our courtship didn’t wake her up.

Actually, the doctors said there’s about 50% probability of a match. Or, to put it another way, 50% of the people who go through the process are deemed not compatible for one reason or another. It could be age, blood type, medical history, or other concerns with their health. The process is thorough to ensure the highest probability of success for the donor and the recipient. If there’s any potential risk concerning the donor, the donor is ruled out.

Let’s look at the scientific reasons to rule someone out vs. the general population:

1) Blood Type – I’m B negative, and can receive organs from someone with O or B blood, positive and negative when it comes to organ donation is not a consideration. The Blood Type breakdown is^[1]:

Using the Caucasian column, since I grew up and live in New Hampshire which is 94% Caucasian^[2], [37+8+9+2] = 56% of the population are potential donors.

2) Age – Different hospitals have different cutoffs for the age of the donor. The concern is for the successful recovery of the donor. The cutoff is typically between 50 and 60 years old.  Since the census data from 2010 breaks it out in an age group from 18-45, we’ll take that data.^[3] 36.5% of the population are potential donors.

3) Liver Parenchyma – More commonly known as liver size, but I learned of the word parenchyma from medical literature. The size of the liver I receive must be at least 1% of my total body weight. The average person has between 2-2.7% (total weight) TW of liver.^[4] A liver is typically broken into two lobes: one lobe is 60% and the other is 40%.  Doing some calculations at my approximate 170lb weight, I need a minimum of 1.7lbs of liver. I could calculate a distribution of probabilities, but let’s just assume the donor has a nominal 2.35% TW liver. That means I need a donor that is at least 120lbs. (120*2.35%*60%>1.7lbs)  And, let’s assume I don’t want a liver larger than I currently have: (x*2.35%*40%<=170*2.35%), so the donor must be less than 720 lbs. I think there would be other concerns at that size. Looking at body weight distributions in the US, the mean for males and females are: 191 and 163lbs, respectively.^[5] I’m not sure of the population distribution, but I think it’s fair to say almost 100% of the population would be a potential donor based on size alone.

4) Previous Surgeries – Previous abdominal surgeries are a no-no. If I were a surgeon, I’d sure want a pristine specimen. One pretty common surgery in the abdominal area is the removal of the gallbladder, which is very close to the liver. There are half a million gall bladder surgeries per year,^[6] and if we look over 30 years and take the US population at 315 million, we’re guessing at approximately 5% of the population have had their gall bladders removed. We’ll use this as a guess at the percentage of the population that has had abdominal surgery, so 95% would likely be eligible for donation.

Using these 4 parameters, any random person in the population has a 20% likelihood of being cleared to be my donor.

Math: (0.56)*(0.365)*(1)*(0.95) = 20%

There you have it. To have over 95% success in finding a donor, I would need to find at least 13 random people to get tested to see if they were a match. So Logan is at least 1 in 14 find, but I would like everyone to know that she’s actually a one in a 7 billion find.

References:
[1] Blood Type Distribution: http://www.redcrossblood.org/learn-about-blood/blood-types
[2] Racial Distribution of NH: http://en.wikipedia.org/wiki/New_Hampshire#Race_and_ancestry
[3] Age Distribution in the US: http://www.census.gov/prod/cen2010/briefs/c2010br-03.pdf
[4] Organ Size and Required Transplant Size: http://ndt.oxfordjournals.org/content/22/suppl_8/viii13.full
[5] Body Weight Distribution in the US: http://www.cdc.gov/nchs/data/ad/ad347.pdf
[6] Gall Bladder surgeries in the US: http://www.obesityaction.org/educational-resources/resource-articles-2/obesity-related-diseases/gallbladder-disease-and-the-obese-patient