Sharmila Manian/LinkedIn

Apr 1, 2026, 11:53

Sharmila Manian: The Mystery of the Positive Direct Coombs Test in Donors

Sharmila Manian, Transfusion Medicine Specialist at Hospital Sultan Ismail, shared a post on LinkedIn:

“The Mystery of the Positive Direct Coombs Test (DCT) in Donors

Why does a perfectly healthy blood donor sometimes test positive on a Direct Coombs Test (DCT)?

It’s a common lab puzzle with a simple explanation.

The ‘Why’: Why do healthy donors test positive?

Biological Variants: Some people naturally carry low-level autoantibodies that cause them zero harm.
Medication Spikes: Common drugs (like certain antibiotics) can make the immune system ‘stick’ to red cells.
Post-Viral Echo: A recent minor cold can leave behind elevated proteins (globulins) that the test picks up.

The ‘Why Not’: Why do we prevent these transfusions?

Even if the donor feels 100% fine, we pull these units from the supply to:

Avoid Lab Delays: These units often show up as ‘incompatible’ during crossmatching, slowing down urgent care.
Protect the Recipient: We aim to eliminate any risk of febrile or hemolytic reactions in the patient.
Maintain Gold Standards: To ensure the highest purity and safety of every bag of blood.

Bottom Line: A positive DCT in a donor is usually a biological quirk, not a medical emergency.

However, for the blood bank, it’s a signal to divert that unit toward research instead of the bedside.”

Sharmila Manian: The Mystery of the Positive Direct Coombs Test in Donors