# Hematopathology Cell Counter > A free manual differential counter for bone marrow aspirates and peripheral blood smears, at https://cellcounter.app/. Last updated 10 October 2026. Hematopathology Cell Counter is a free manual differential counter for bone marrow aspirates and peripheral blood smears. Tap a cell tile, or press its keyboard key, for each cell you identify under the microscope. The app keeps the running differential, the myeloid-to-erythroid (M:E) ratio and a separate nRBC count, then produces a clean report you can copy, print to PDF or share. It is a counting aid for hematopathologists and laboratory staff, and it does not diagnose, classify risk or recommend treatment. Open the counter at https://cellcounter.app/. It runs in the browser, with nothing to install. ## At a glance - What it counts: bone marrow aspirate differentials (myelograms) and peripheral blood smear (PBS) differentials - Who it is for: hematopathologists, pathologists, residents and clinical laboratory professionals - Where it runs: any current web browser at cellcounter.app; also built for iPhone, iPad and Android - Where your data lives: only on your device. No account, no sign-in, no server-side copy - Cost: free on the web - Made by: Zehra Nur Kocas-Kilicarslan, MD, and Alican Kilicarslan, MSc - Also known as: Cell Counter ## What it does - Templates for marrow and blood: built-in Bone Marrow Aspirate, PBS Five-Part and PBS Extended / Immature Myeloid templates, ready to count. - Keyboard counting on the web: every cell tile shows its key. Press it to count, use the number pad if you like, and undo with ⌘Z or Ctrl+Z without looking up from the microscope. - Targets, up or down: count up to a target or down from it, with preset or custom targets. At the target the app asks, keeps counting or stops, as you choose. - Undo, redo and history: mistaps come straight back. A count history lists every action, and a same-cell press guard ignores accidental rapid repeats. - Live lineage summary: follow myeloid and erythroid totals and the M:E ratio as you count, with a blast subtotal in the report. - nRBC on its own channel: nucleated red cells are counted separately, reported per 100 WBC, and feed an optional corrected WBC calculator. - Quality-control checkpoints: milestone checkpoints, such as 100, 200 and 500 cells on a marrow count, prompt a quick review. They are reminders and never change a count. - Your grid, your order: drag cells into the order you read a slide, remove the ones you skip, add cells from a searchable cell library, and save the result as your own template. - Template sharing: export a template as a file and import it on another device or at a colleague's bench. Imports are checksum-verified and never overwrite anything. - Reports in one tap: counts and percentages, lineage totals, M:E ratio, nRBC section, checkpoint log and notes. Copy as text, print or save as PDF, or share. - Never lose a count: every press is saved as it happens. Close the tab mid-count and it is restored, or pause and resume later from the Archive. - Archive and revisions: reports and drafts are kept on the device. Search by case label, duplicate a count or continue a report as a revision. ## Built-in templates | Template | Default target | Cells | | --- | --- | --- | | Bone Marrow Aspirate | 500 cells | 20 cell types: myeloblast, promyelocyte, myelocyte, metamyelocyte, band and segmented neutrophils; eosinophilic and basophilic precursors, eosinophils and basophils; monocytic precursors and monocytes; proerythroblasts and basophilic, polychromatic and orthochromatic erythroblasts; lymphocytes, plasma cells, megakaryocytes and lymphoblasts. Includes the M:E ratio. | | PBS Five-Part | 100 cells | Segmented neutrophils, lymphocytes, monocytes, eosinophils and basophils, with nRBCs counted separately. | | PBS Extended / Immature Myeloid | 100 cells | The five-part cells plus band neutrophils, metamyelocytes, myelocytes, promyelocytes and myeloblasts, with nRBCs counted separately. | ## How a count works 1. Open https://cellcounter.app/ and choose a template. 2. Set the target and whether to count up or down. 3. Tap each cell's tile, or press its key, as you identify it on the slide. 4. Acknowledge any quality-control checkpoint you reach along the way. 5. At the target, review the differential and generate the result. 6. Copy, print to PDF or share the report. It stays in the Archive, ready to revise. ## How the numbers are calculated Every cell carries three settings that are independent of each other and of its name, colour, group and position: its counting channel (main differential or counted separately), whether it counts toward the differential total, and its M:E lineage role (myeloid, erythroid or excluded). Renaming or reordering a cell never changes a result. - Percentage of a cell type: cell count ÷ differential total × 100 - M:E ratio: myeloid total ÷ erythroid total. Reported as not calculable when no erythroid cells were counted. - nRBC per 100 WBC: nRBC count × 100 ÷ differential total - Corrected WBC (optional): uncorrected WBC × 100 ÷ (100 + nRBC per 100 WBC). Use it only for a WBC value that has not already been corrected for nRBC; many analysers already apply this correction, and applying it twice understates the result. A value that cannot be calculated, for example when the denominator is zero, is shown as not calculable rather than as zero or infinity. Rounding happens only when a value is displayed. ## Privacy and your data Counts, reports, templates and case labels are stored only on your device: in the browser's IndexedDB on the web and in SQLite on iOS and Android. There is no account, no sign-in and no server that holds your counts. Clearing the browser's site data removes them. Use non-identifying case labels such as "Bench 3". The app warns when a label looks like a person's name, a date of birth or an accession or record number. The web app uses no analytics or advertising trackers; it reports software errors so that bugs can be fixed. ## Who made it Hematopathology Cell Counter is built by Zehra Nur Kocas-Kilicarslan, MD, and Alican Kilicarslan, MSc, for the people who count cells at the microscope every day. ## Frequently asked questions ### Is Hematopathology Cell Counter free, and do I need an account? The web app at cellcounter.app is free and needs no account, sign-in or installation. Open it in a current browser and start counting. ### Can it count both bone marrow aspirates and peripheral blood smears? Yes. It ships with three templates: Bone Marrow Aspirate (20 cell types, 500-cell default target), PBS Five-Part (100-cell default target) and PBS Extended / Immature Myeloid (100-cell default target). You can edit any of them into your own templates. ### How many cells does it count by default? The built-in templates default to 500 cells for a bone marrow aspirate and 100 cells for a peripheral blood smear. You can pick another preset or enter any custom target, count up to it or down from it, and choose whether counting asks, continues or stops at the target. ### How does the app calculate the M:E ratio? The M:E ratio is the total of cells whose lineage role is myeloid divided by the total of cells whose lineage role is erythroid. Each cell's role is set on its own and never inferred from its name, group or position. If no erythroid cells were counted, the ratio is reported as not calculable rather than as zero or infinity. ### Are nucleated red blood cells included in the WBC differential? No. nRBCs are counted on a separate channel, never enter the differential total and never advance the WBC target. The report gives nRBC per 100 WBC, and an optional calculator corrects a WBC value that has not already been corrected: uncorrected WBC × 100 / (100 + nRBC per 100 WBC). ### Can I count with the keyboard? Yes. On the web every cell tile shows its shortcut key. Press it to count that cell, use the number pad if you prefer, and press ⌘Z or Ctrl+Z to undo. Shortcuts are editable per template and checked for collisions. ### Where is my data stored, and can I enter patient identifiers? Counts, reports, templates and case labels are stored only on your device: in the browser's IndexedDB on the web and in SQLite on iOS and Android. There is no account and no server-side copy. Use non-identifying case labels; the app warns when a label looks like a name, a date of birth or an accession or record number. ### Can I customise templates and share them with colleagues? Yes. Reorder, remove or add cells, set shortcut keys and save the grid as your own template. Templates export as files that a colleague can import; imports are verified against checksums and always create a new template rather than replacing an existing one. ### Does the app diagnose or interpret results? No. Hematopathology Cell Counter is a professional counting aid. It records and totals what you count and formats the report; interpretation stays with the hematopathologist. It does not provide diagnoses, risk classification or treatment recommendations. ## Professional use A counting aid, not a diagnostic device. Hematopathology Cell Counter does not provide diagnoses, risk classification or treatment recommendations. Results reflect what the user counted and must be reviewed by a qualified professional.