What is the corrected WBC formula for NRBCs?

Corrected WBC = (uncorrected WBC × 100) ÷ (100 + NRBCs per 100 WBCs). The NRBC input is the number observed while enumerating 100 WBCs on a peripheral blood smear.

Do all automated analyzers need this correction?

No. Some modern analyzers enumerate WBCs and NRBCs separately and report a WBC that is not affected by NRBCs. Confirm the analyzer result and laboratory procedure first; otherwise the value can be corrected twice.

Can I use this for a traumatic lumbar puncture or CSF sample?

No. CSF WBC correction for blood contamination is a different calculation using CSF and peripheral-blood values. This calculator is only for NRBC interference in peripheral blood.

Why does the result not say normal, high, or low?

WBC reference intervals vary with age, pregnancy, laboratory method, and clinical context. Compare the result only with the interval on the relevant report and have it interpreted by a qualified professional.

Which units are supported?

×10³/µL, K/µL, and 10⁹/L have the same numeric value. Cells/µL and cells/mm³ also have the same numeric value and are 1,000 times the ×10³/µL value.

Corrected WBC for NRBCs Calculator

Enter an uncorrected WBC and NRBCs counted per 100 WBCs to calculate the corrected count, numerical difference, and worked formula.

Check before calculating

Use only for an uncorrected peripheral-blood WBC with NRBCs reported per 100 WBCs.
Do not recalculate a WBC that the analyzer or laboratory has already corrected.
This is not the formula for CSF blood contamination and does not diagnose leukopenia or leukocytosis.

Peripheral blood values

Use values from the same report and smear review.

Formula

Corrected WBC = (uncorrected WBC × 100) ÷ (100 + NRBC)

Result

Enter both values and select Calculate.

Interpretation and sources

This tool performs arithmetic only. Compare the corrected value with the age-, pregnancy-, method-, and laboratory-specific reference interval on the report. A qualified laboratory professional or clinician must determine whether correction is appropriate.

Formula: LSU Health Sciences Center, The Hemogram. Analyzer limitation: Sysmex automated NRBC counting. Accessed September 17, 2026.

Privacy: values are calculated in your browser and are not submitted by this form.

Summary

Enter an uncorrected WBC and NRBCs counted per 100 WBCs to calculate the corrected count, numerical difference, and worked formula.

How it works

Confirm that the laboratory value is an uncorrected WBC or total nucleated cell count.
Select the same unit used on the report: ×10³/µL (numerically equal to 10⁹/L) or cells/µL (/mm³).
Enter the NRBCs observed while counting 100 WBCs on a peripheral blood smear.
Review the corrected count, numerical difference, percentage change, and substituted formula.

Use cases

Performing the manual NRBC correction specified by a laboratory procedure.
Checking the arithmetic on a peripheral-blood smear differential worksheet.
Seeing how much NRBC inclusion changes an uncorrected nucleated-cell count.
Expressing the calculation in ×10³/µL, 10⁹/L, K/µL, cells/µL, or /mm³.

Frequently Asked Questions

Last updated: 2026-09-19 · Reviewed by Nham Vu