How is paternity of a child determined by blood type analysis? Not a DNA test, but the "old fashioned" way?

Apparently, in the pre-DNA world, you could determine the paternity of a child by drawing blood from both the father and child, find their blood types, then confirm that the child could not possibly be the child of the alleged father. How is this done? Who can run this test?

Certain blood types can only produce certain blood types.

So a father with AB+ blood and a mom with B+ blood can only have a child with A+,AB+,B+ blood. If the man is O- blood he can't be the dad.

My example with the specific blood types may be incorrect but thats the general idea of it.

phlebotomists and med lab technicians ran these tests

basically you just drew blood, mixed it with anti-a, anti-b, and anti-d reagents

if you saw clumping with anti-a, it means they're type a
if you saw clumping with anti-b, it means they're type b
if you see clumping with anti-d, it means that they're rH positive (determines positive or negative blood type)

if you see clumping with anti-a and anti-b, the person is blood type AB

if you dont see clumping with anti-a and anti-b, the person is blood type O

i know this is correct because i ran those kinds of tests

There are actually 20 some odd blood types beyond ABO and Rh. By typing out both parents and the childs blood, it becomes possible to estimate whether a man is father of this child or not. This method of course is not as certain as DNA testing since DNA has virtually infinite combinations and so a match would be regarded with certainty. By blood type testing with relatively few possible combinations, there can literally be thousands of men whou clould fit the profile for paternity.