MAGENT

Absolute lymphocyte count: the ALC formula and Shapiro 1998 cutoffs

The absolute lymphocyte count (ALC) turns the lymphocyte percentage on a blood count into a number of cells per microlitre. Multiply the white cell count by the lymphocyte percentage and divide by 100. This ALC calculator does that sum, rounds to a whole number and places the result in one of the three bands from Shapiro 1998.

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

Use this calculator via API

What is the absolute lymphocyte count?

A blood count report usually gives lymphocytes two ways: as a share of all white cells and as an absolute number. The absolute number is what you get when the share is applied to the total. If the white cell count is 6,000 cells/µL and 20% of them are lymphocytes, the ALC is 1,200 cells/µL.

Shapiro and colleagues looked at whether the ALC could stand in for a CD4 count. The calculator reports their two cutoffs as bands. It doesn't estimate a CD4 count.

The ALC formula

ALC (cells/µL) = WBC (cells/µL) × lymphocyte % ÷ 100

WBC in 10^3/µL is multiplied by 1000 first
result rounded to the nearest whole cell

Exact expression the calculator uses:

ALC_per_uL = wbc_per_uL * lymphocyte_percent / 100

Inputs

InputMeaningRange
wbc_k_ulWhite cell count in 10^3/µL (the same as 10^9/L)0.01 to 500
wbc_ulWhite cell count in cells/µL, if you'd rather enter it that way10 to 500000
lymphocyte_percentLymphocytes as a percentage of white cells0.1 to 99

Give one of the two white cell inputs, not both.

How the calculation works

  1. Put the white cell count in cells/µL. A value in 10^3/µL is multiplied by 1000.
  2. Apply the percentage. Multiply by the lymphocyte percentage and divide by 100.
  3. Round to the nearest whole cell.
  4. Assign the band:
ALC (cells/µL)BandShapiro 1998 reading
Below 1000<1000predicts CD4 below 200
1000 to 19991000-1999between the two cutoffs
2000 or more>=2000predicts CD4 of 200 or more

Cells/mm³ and cells/µL are the same unit, so the cutoffs carry over directly.

Worked examples

These use Magent's own expected values for the calculator.

Example 1: WBC 6.0 with 20% lymphocytes

  1. 6.0 × 1000 = 6000 cells/µL.
  2. 6000 × 20 ÷ 100 = 1200.
  3. ALC 1200 cells/µL, band 1000-1999.

Example 2: WBC 6.0 with 50% lymphocytes

  1. 6.0 × 1000 = 6000 cells/µL.
  2. 6000 × 50 ÷ 100 = 3000.
  3. ALC 3000 cells/µL, band >=2000.

Example 3: the same count entered in cells/µL

  1. The white cell count is entered as 6000 cells/µL, so no conversion is needed.
  2. 6000 × 50 ÷ 100 = 3000.
  3. ALC 3000 cells/µL, band >=2000, matching Example 2.

History of the ALC cutoffs

Shapiro and colleagues published "Absolute lymphocyte count as a predictor of CD4 count" in Annals of Emergency Medicine in 1998. The two cutoffs the calculator uses come from that paper.

When it's used

Whenever an absolute lymphocyte number is wanted from a white cell count and differential, and when someone wants to see where it falls against the Shapiro 1998 cutoffs.

Where it's used

Emergency departments, clinics, laboratories and teaching.

Who uses it

Doctors, nurses, laboratory staff and students. The calculator does the multiplication and the banding.

Limits of the calculation

  • The result is no better than the white cell count and differential it comes from. The calculator doesn't measure either.
  • An ALC isn't a CD4 count. The bands report the Shapiro 1998 cutoffs; they don't estimate CD4.
  • The cutoffs come from one study.
  • This page doesn't say what a count means for a particular person.

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

Glossary

  • Lymphocyte: a type of white blood cell.
  • Differential: the breakdown of white cells into types, as percentages.
  • CD4 count: a count of one kind of lymphocyte, measured separately.
  • cells/µL: cells per microlitre, the same as cells/mm³.

Common mistakes

  • Forgetting the unit of the white cell count. 6.0 in 10^3/µL is 6000 cells/µL.
  • Entering the percentage as a fraction. 20% is entered as 20, not as a decimal.
  • Reading the band as a CD4 result. It isn't one.

Source

Shapiro NI, et al. Absolute lymphocyte count as a predictor of CD4 count. Ann Emerg Med. 1998;32(3):323-328. DOI: 10.1016/s0196-0644(98)70008-3. PMID: 9737494

Frequently asked questions

How do you calculate the absolute lymphocyte count?

Multiply the white cell count in cells/µL by the lymphocyte percentage and divide by 100.

What do the ALC bands mean?

They're the Shapiro 1998 cutoffs: below 1000 predicted a CD4 count below 200, and 2000 or more predicted a CD4 count of 200 or more. Values from 1000 to 1999 fall between them.

Is the ALC a CD4 count?

No. It counts all lymphocytes. A CD4 count is a separate test.

Can I enter the white cell count in cells/µL?

Yes. Use wbc_ul instead of wbc_k_ul.