How Accurate Is the Eldon Card for Field Blood Typing?

Researched and written by Mike Shertz, MD/18D, not AI

🕖 Reading Time, 4 minutes

Multiple methods of ABO blood typing are approved by the US FDA. Nearly all of them require specialized instruments and chemical reagents, and those items are rarely, if ever, available in a truly austere setting.

The Eldon card is a dry reagent, field friendly ABO Rh blood typing kit. The manufacturer reports 99.9% accuracy compared to more traditional ABO Rh blood typing techniques. That figure describes the card. It does not describe the person holding it.

The card is accurate. The operator is the variable.

In a study of 377 volunteer student Naval Hospital Corpman and individuals preparing for deployment at the Defense Medical Readiness Training Institute, evaluated on their ability to use an Eldon card kit correctly and properly interpret the results, using their own finger-prick blood, their ability to do so was only 80%.¹

The failures were procedural, not chemical

Common failure points were:

Failure to add water to the test field
Blood sample not spread evenly enough to cover the test field
The stirring stick from one field used on another, cross-contaminating it
Not rotating the card to help visualize the reaction

All of these were attributed to user error. Apparently, it is easier if you read the directions.¹

Accuracy dropped even when the card was already prepared

When volunteers were asked to identify blood types on premade cards, their accuracy was 94% for O POS, 92% for O NEG, and 90% for A POS.¹

Heat, cold, and humidity do not degrade the card

The obvious follow-up question: how accurate is the Eldon card after it has been sitting in a deployed location for months with no environmental protection?

A military research study examined the Eldon blood typing kit’s accuracy across a range of operational temperature and humidity levels, and its stability in long-term storage from -30C to 50C for one to nine months.²

The test conditions matched real deployment climates

Accuracy was tested by typing previously identified known blood type samples with Eldon cards inside an environmental chamber: high temperature with low humidity at 41C, high temperature with high humidity at 33C, and low temperature at 6C with both high and low humidity. Those conditions correlated with weather in Kuwait and Okinawa. Researchers tested each condition, environment, and duration on hundreds of Eldon cards.

Field conditions did not change the result

Eldon cards performed equally whether the blood typing occurred at room temperature or under the environmental conditions above. Accuracy determining O POS was 100% and O NEG was 99%.²

Nine months of storage abuse did not change it either

Even prolonged environmental exposure of as much as nine months, from a low of -30C to a high of 50C, did not significantly affect blood typing results. Accuracy in determining O POS was 98%, and O NEG was 95%.²

The Joint Trauma System already ranks Eldon-typed blood last

JTS Clinical Practice Guideline ID:82 (dated 30 Oct 2020) addresses prehospital blood transfusion. In its ranking of desirable blood products, fresh group O whole blood of unknown titer drawn from a walking blood bank and typed by Eldon card or equivalent sits at the bottom of the list. Given the Eldon card’s documented field accuracy, that placement is reasonable.³

What this means to you

The Eldon card is an environmentally stable field method for determining ABO Rh blood type, with high but nowhere near perfect degree of accuracy.

Given the potential severity of a hemolytic transfusion reaction, the Eldon card is best used to verify blood types rather than to determine them de novo. If you are going to use it to identify previously untyped blood donors, you will need to follow the old skydiving adage: everything will be fine, just do not screw up a single thing.

Reading the directions and comparing your results against the interpretation card will help.

See how we integrate the medical literature into our online courses.

References

¹ Bienek DR, Perez NM. Diagnostic accuracy of a point-of-care blood typing kit conducted by potential end users. Mil Med. 2013 May;178(5):588-92. doi:10.7205/MILMED-D-12-00500. PMID: 23756020.

² Bienek DR, Charlton DG. Accuracy of user-friendly blood typing kits tested under simulated military field conditions. Mil Med. 2011 Apr;176(4):454-60. PMID: 21539170.

³ Voller J, Tobin JM, Cap AP, et al. Joint Trauma System Clinical Practice Guideline (JTS CPG): Prehospital Blood Transfusion, CPG ID:82. 30 October 2020. Reprinted in J Spec Oper Med. 2021;21(4):11-21. PMID: 34969121.

Mike Shertz MD/18D

Dr. Mike Shertz is the Owner and Lead Instructor at Crisis Medicine. Dr. Shertz is a dual-boarded Emergency Medicine and EMS physician, having spent over 30 years gaining the experience and insight to create and provide his comprehensive, science-informed, training to better prepare everyday citizens, law enforcement, EMS, and the military to manage casualties and wounded in high-risk environments. Drawing on his prior experience as an Army Special Forces medic (18D), two decades as an armed, embedded tactical medic on a regional SWAT team, and as a Fire Service and EMS medical director. Using a combination of current and historical events, Dr. Shertz’s lectures include relevant, illustrative photos, as well as hands-on demonstrations to demystify the how, why, when to use each emergency medical procedure you need to become a Force Multiplier for Good.