Corrected count increment (CCI): how the platelet transfusion formula works

The corrected count increment (CCI) is the rise in platelet count after a platelet transfusion, multiplied by body surface area and divided by the number of platelets transfused (in units of 10^11). A rise from 10000 to 30000 per µL, a body surface area of 1.8 m² and 3 × 10^11 platelets transfused give a CCI of 12000.

Not a medical device. Not a diagnosis or dosing recommendation.

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Hematology calculators
Davis KB et al. · 1999
The corrected count increment formula
Worked examples
Frequently asked questions

What is the corrected count increment?

The corrected count increment puts platelet transfusion responses on a common footing. A bigger person, or more platelets in the bag, would be expected to change the raw rise in count, so the CCI scales the rise by body surface area and by the number of platelets transfused. The calculator cites Davis, Slichter and Corash, Transfusion, 1999.

This CCI is not the Charlson Comorbidity Index. The two share an abbreviation and nothing else. For the comorbidity score, see the Charlson calculator.

Magent's calculator returns the raw increment and the CCI, both as whole numbers. It doesn't apply a cutoff or label the result.

This page explains the arithmetic. It doesn't say what a value means for a particular person.

The corrected count increment formula

increment = post-transfusion platelet count − pre-transfusion platelet count   (per µL)
CCI = increment × body surface area (m²) ÷ platelets transfused (× 10^11)
both rounded to whole numbers

Exact expression the calculator uses:

cci = (post_plt_per_ul - pre_plt_per_ul) * bsa_m2 / platelets_transfused_e11

Inputs

Input	Meaning	Accepted range
`pre_plt_per_ul`	Platelet count before the transfusion, per µL	0 to 2000000
`post_plt_per_ul`	Platelet count after the transfusion, per µL; at least the pre count	0 to 2000000
`bsa_m2`	Body surface area you supply, m²	0.1 to 4.0
`platelets_transfused_e11`	Platelets transfused, already in units of 10^11 (3 means 3 × 10^11)	0.1 to 50

How the calculation works

Increment: post-transfusion count minus pre-transfusion count.
Multiply the increment by body surface area.
Divide by the platelets transfused, expressed in units of 10^11.
Round the increment and the CCI to whole numbers.

A larger body surface area raises the CCI for the same increment. More platelets transfused lowers it.

Units

Platelet counts are per µL. The per-µL count gives the same increment as a count in × 10^9/L once the units are matched. Body surface area is in m² and comes from you; the calculator doesn't work it out from height and weight. Platelets transfused are entered in units of 10^11, so 3 means 3 × 10^11 platelets. A post count lower than the pre count, or a value outside its range, is rejected with an error.

Worked examples

These use Magent's own expected values for the calculator. Each transfusion is 3 × 10^11 platelets.

Example 1: pre 10000, post 30000, BSA 1.8 m²

Increment = 30000 − 10000 = 20000 per µL.
CCI = 20000 × 1.8 ÷ 3 = 12000.

Example 2: pre 10000, post 20000, BSA 1.2 m²

Increment = 20000 − 10000 = 10000 per µL.
CCI = 10000 × 1.2 ÷ 3 = 4000.

Example 3: pre 10000, post 40000, BSA 2.0 m²

Increment = 40000 − 10000 = 30000 per µL.
CCI = 30000 × 2.0 ÷ 3 = 20000.

Example 4: no rise, BSA 1.8 m²

Increment = 10000 − 10000 = 0.
CCI = 0.

History of the corrected count increment

The calculator cites Davis KB, Slichter SJ and Corash L, Corrected count increment and percent platelet recovery as measures of posttransfusion platelet response: problems and a solution, Transfusion, 1999 (volume 39, issue 6, pages 586–592). Their abstract describes the CCI and the percent platelet recovery (PPR) as measures that correct the count increment for blood volume and for the number of platelets transfused. It goes on to describe how these ratios can distort comparisons of platelet products, and suggests regression analysis of posttransfusion increments instead. The authors also advised against using the CCI or PPR to define platelet refractoriness as a study outcome. Their data came from the first platelet transfusion in the Trial to Reduce Alloimmunization to Platelets (TRAP).

When it's used

The CCI describes the platelet count response to a single platelet transfusion, using counts taken before and after it.

Where it's used

The inputs are two platelet counts, a body surface area and the number of platelets transfused, which comes from the platelet product.

Who uses it

The person using the calculator enters the two counts, a body surface area they already have and the platelets transfused in units of 10^11. The calculator does the subtraction, multiplication and division.

Limits of the calculation

The calculator doesn't measure platelet counts, work out body surface area, or count the platelets in a unit.
It doesn't apply a refractoriness cutoff. Published cutoffs differ, and Davis and colleagues argued against using the CCI to define refractoriness as a study outcome.
The 1999 paper cautions that the CCI can distort comparisons between platelet products.
It isn't an order for another transfusion.
This page doesn't say what to do with a value.

Clinical decisions belong to a qualified clinician who knows the patient.

Charlson Comorbidity Index sums weighted comorbidities. It has no connection to platelet transfusion.
Body surface area (Mosteller) works out body surface area from height and weight; the CCI calculator expects you to supply that number.
Allowable blood loss estimates blood loss from blood volume and hematocrit values, not platelet counts.

Glossary

Increment: post-transfusion platelet count minus pre-transfusion count.
Body surface area (BSA): in m², supplied by you.
Platelets transfused: the number of platelets given, in units of 10^11.
PPR: percent platelet recovery, a related measure described alongside the CCI in the 1999 paper. This calculator doesn't return it.
Refractoriness: a poor response to platelet transfusion. The calculator doesn't label it.

Common mistakes

Mixing it up with the Charlson index. Same abbreviation, unrelated calculation.
Entering the raw platelet number. Enter platelets transfused in units of 10^11: 3 × 10^11 is entered as 3.
Mixing count units. Enter both counts per µL.
Leaving out body surface area. It's a required input, and the calculator doesn't estimate it.

Source

Davis KB, Slichter SJ, Corash L. Corrected count increment and percent platelet recovery as measures of posttransfusion platelet response: problems and a solution. Transfusion. 1999;39(6):586-592. DOI: 10.1046/j.1537-2995.1999.39060586.x. PMID: 10378838

Frequently asked questions

How do you calculate the corrected count increment?

Subtract the pre-transfusion platelet count from the post-transfusion count, multiply by body surface area in m², and divide by the platelets transfused in units of 10^11.

Is the corrected count increment the same as the Charlson Comorbidity Index?

No. Both are called CCI, but the corrected count increment is about platelet transfusion and the Charlson index sums comorbidities.

What units do the platelet counts use?

Per µL, for both the pre- and post-transfusion counts.

How are platelets transfused entered?

In units of 10^11. Three hundred billion platelets is 3 × 10^11, entered as 3.

Does the calculator say whether the response is adequate?

No. It returns the increment and the CCI with no cutoff or label.