Crossmatch to Transfusion Ratio Calculator
Crossmatch to Transfusion Ratio Calculator
The oldest measure of blood ordering efficiency, with the transfusion probability alongside it. A ratio above 2 means units are being reserved and returned rather than used.
Crossmatch to Transfusion Ratio
Crossmatched ÷ transfused210 units crossmatched, 100 transfused; 100 patients crossmatched, 28 transfused
Formula
Transfusion probability (%T) = patients transfused ÷ patients crossmatched × 100
Transfusion index (TI) = units transfused ÷ patients crossmatched
- C:T at or below 2.0
- the benchmark now usually quoted for efficient blood use. Boral and Henry's original 1977 figure was 2.5, and both are still in circulation — say which you are auditing against
- %T of 30% or more
- Mead's transfusion probability. Below 30%, most of the patients being crossmatched never receive blood, which is an argument for type and screen rather than for a tighter crossmatch policy
- TI of 0.5 or more
- the transfusion index — average units transfused per patient crossmatched. Below 0.5, a procedure does not warrant a routine crossmatch at all
- the same period, the same denominator
- all four counts must come from one audit window. Mixing a month of crossmatches with a quarter of transfusions produces a ratio that means nothing
Worked example
210 units crossmatched, 100 transfused; 100 patients crossmatched, 28 transfused
210 ÷ 100 = 2.10
Above the 2.0 target, though below the original Boral and Henry figure of 2.5
Transfusion probability = 28 ÷ 100 × 100 = 28%, below the 30% benchmark
Transfusion index = 100 ÷ 100 = 1.0, comfortably above 0.5
The pattern — an acceptable transfusion index but a low transfusion probability — says a minority of patients are consuming most of the blood while the majority are crossmatched needlessly
The three blood utilisation indices
| Index | Formula | Benchmark |
|---|---|---|
| Crossmatch to transfusion ratio (C:T) | Units crossmatched ÷ units transfused | 2.0 or below; Boral and Henry originally proposed 2.5 |
| Transfusion probability (%T) | Patients transfused ÷ patients crossmatched × 100 | 30% or above |
| Transfusion index (TI) | Units transfused ÷ patients crossmatched | 0.5 or above |
What actually lowers a high ratio
| Change | How it works |
|---|---|
| Maximum surgical blood order schedule (MSBOS) | Sets an agreed number of units per procedure from local audit, replacing habit-based ordering |
| Type and screen instead of crossmatch | Removes the crossmatch entirely for procedures that rarely transfuse; blood is issued only if it is needed |
| Electronic issue (computer crossmatch) | Issues group-compatible red cells in minutes to eligible patients with no serological crossmatch, so nothing is reserved in advance |
| Remote electronic release from satellite fridges | Shortens the time a unit spends allocated to one patient and unavailable to everyone else |
| Shorter reservation periods | Returns unused units to general stock sooner, preserving usable shelf life |
A ratio that measures a policy, not a patient
The crossmatch to transfusion ratio is the oldest and simplest measure of how well a hospital orders blood: units crossmatched divided by units transfused over an audit period. A ratio of 1.0 would mean every unit crossmatched was used, which no service achieves or should. The benchmark now usually quoted is 2.0 or below, although Boral and Henry, who introduced the measure alongside the type and screen in 1977, proposed 2.5. Both figures are still in the literature, so an audit should say which it is using.
A high ratio is not a harmless inefficiency. A crossmatched unit is allocated to one named patient for the length of the reservation period and unavailable to anyone else, so over-ordering effectively shrinks the usable inventory and pushes units towards their expiry date without ever reaching a patient. It also consumes technologist time on serological work that was never needed. In a group with high demand and a short shelf life, that is a real cost rather than a paper one.
The ratio is most informative read next to the transfusion probability — the percentage of crossmatched patients who received any blood at all, benchmarked at 30% or more — and the transfusion index, the average units transfused per patient crossmatched, benchmarked at 0.5 or more. The three separate two different problems. A low transfusion probability with an acceptable transfusion index means a few patients are consuming most of the blood while the majority are crossmatched for nothing, which is a case for type and screen. A high probability with a high ratio means the right patients are being crossmatched but for too many units each, which is a case for revising the order schedule.
What actually moves the number is procedural rather than exhortatory. A maximum surgical blood order schedule replaces habit with an agreed number of units per operation, derived from the hospital's own audit. Type and screen removes the crossmatch entirely for procedures that rarely transfuse, and electronic issue lets a laboratory release group-compatible red cells within minutes to eligible patients without reserving anything in advance. Together these have made routine pre-operative crossmatching obsolete for most elective surgery, and they are the reason a C:T ratio that was normal in 1980 would be considered poor practice now.
Frequently asked questions
What is a good crossmatch to transfusion ratio?
At or below 2.0 is the benchmark usually quoted today. Boral and Henry's original 1977 proposal was 2.5, and both figures remain in circulation, so an audit should state which one it is measuring against.
How is transfusion probability calculated?
Patients transfused divided by patients crossmatched, multiplied by 100. A value of 30% or more is the accepted benchmark. Below that, most of the patients being crossmatched never receive blood, which is an argument for type and screen.
Why does a high C:T ratio matter?
A crossmatched unit is reserved for one patient and unavailable to anyone else for the reservation period, so over-ordering shrinks usable inventory, pushes units towards expiry without reaching a patient, and consumes technologist time on serology nobody needed.
What is a maximum surgical blood order schedule?
An agreed list of how many units to crossmatch, or whether to crossmatch at all, for each surgical procedure, derived from the hospital's own transfusion audit. It replaces habit-based ordering and is the single most effective way to lower a high C:T ratio.
What is the transfusion index?
Units transfused divided by patients crossmatched — the average number of units the typical crossmatched patient actually receives. A value of 0.5 or more indicates worthwhile use; below that, the procedure does not justify a routine crossmatch.
Related calculators
References
- Boral LI, Henry JB. The type and screen: a safe alternative and supplement in selected surgical procedures. Transfusion. 1977;17(2):163–168.
- Mead JH, Anthony CD, Sattler M. Hemotherapy in elective surgery. An incidence report, review of the literature, and alternatives for guideline appraisal. Am J Clin Pathol. 1980;74(2):223–227.
- Milkins C, Berryman J, Cantwell C, et al. Guidelines for pre-transfusion compatibility procedures in blood transfusion laboratories. Transfus Med. 2013;23(1):3–35.