Thymidine Incorporation Assays


Cell proliferation studies based on the thymidine incorporation assay are employed frequently in immunological, cancer, stem cells, and pharmaceutical research to assess the ability both of natural and synthetic compounds to stimulate or inhibit the proliferation of lymphocytes and other cells.

Cell proliferation assays measure the incorporation of a radiolabeled DNA precursor, 3H- or 14C- thymidine, into the replication strands of DNA produced during cell division. Cultures are typically set up in microplates. The labeled DNA is usually captured with a cell harvester on glass fiber filters discs, which are then placed in liquid scintillation counting vials or directly harvested into a filter plate for counting on a scintillation beta-counter. The assay can also be performed using a scintillating Cytostar-T® plate, which requires no filtration step or scintillation cocktail.

Thymidine Uptake Assay
Thymidine uptake assay


What do I need to run this assay

Filtration format

Reagents available from PerkinElmer:

  • Radiolabeled thymidine (see next section)
  • TC-treated microplates for cell culturing (we recommend CulturPlates™)
  • Glass fiber filters (UniFilter plates or Filtermat)
  • Scintillation cocktail or Meltilex® solid scintillant (Cat. No. 1450-441) (if using Filtermat)
  • Scintillation vials (if using filter discs)
  • Cell harvester
  • TopSeal-A™ (Cat. No. 6050185) and BackSeal (Cat. No. 6005199) (if using UniFilter plates)
  • Radiometric detector (such as a Tri-Carb® liquid scintillation counter, or a high-throughput detector such as a TopCount® or MicroBeta®)

Reagents available from other suppliers:

  • Stimulation factors
  • Trypsin
  • Wash buffer (e.g. PBS)

Cytostar-T format

  • Cytostar-T plates (Cat. No. RPNQ0162 for 96-well, RPNQ0165 for 384-well)
  • TopSeal-A™ adhesive plate seal (Cat. No. 6050185)
  • White backseal, if counting from the top (Cat. No. 6005199)
  • Radiolabeled thymidine (see next section)
  • High-throughput radiometric detector (such as a TopCount or MicroBeta)
  • Cell culture medium, buffer for labeling
  • Stimulation factors


Products and catalog numbers

Thymidine radiochemicals

ApplicationCompoundSpecific activityRad. conc. (mCi/mL)Packaging bufferStorage temp.NotesCat. number
DNA proliferation                  Thymidine, [methyl-14C]  40-60 mCi/mmol0.1Steri-packaged, aqueous solution5°C NEC568
50-62 mCi/mmol0.05Steri-packaged, aqueous solution5°C NEC568D
Thymidine, [methyl-3H]              2 Ci/mmol1Steri-packaged, aqueous solution5°CRecommend use within one month of receiptNET027A
6.7 Ci/mmol1Steri-packaged, aqueous solution5°CRecommend use within one month of receiptNET027
20 Ci/mmol1Steri-packaged, aqueous solution5°CRecommend use within one month of receiptNET027X
20 Ci/mmol170% ethanol-20°C NET027E
23-27 Ci/mmol110% ethanol5°C NET027L
40-60 Ci/mmol12% ethanol5°C NET027W
70-90 Ci/mmol1Steri-packaged, aqueous solution5°CRecommend use within one month of receiptNET027Z
100-130 Ci/mmol12% ethanol5°CRecommend use within one month of receiptNET512V
Total nucleic acid proliferation    Thymidine, [2-14C]>50 mCi/mmol0.1Steri-packaged, aqueous solution5°C NEC156
Thymidine, [6-3H]  >10 Ci/mmol1Steri-packaged, aqueous solution5°C NET355
5-6 Ci/mmol1Steri-packaged, aqueous solution5°C NET355L
DNA probe labeling        Deoxythymidine triphosphate, [methyl-3H]        10-25 Ci/mmol150% ethanol-20°C NET221H
70-90 Ci/mmol150% ethanol-20°C NET221X
70-90 Ci/mmol2.510 mM Tricine buffer pH 7.6-80°C NET221A


Choose the right thymidine


  • Total vs. DNA only proliferation: Thymidine will label both DNA and RNA. 3H-methyl-thymidine (thymidine labeled on the methyl group) will only label DNA.
  • Stability vs. toxicity: Formulations containing ethanol will last longer in storage, however may kill cells. Formulations without ethanol are less toxic to cells, but have a shorter shelf life.
  • Ease vs. flexibility: fixed specific activity means that the same volume can be used everytime. Products with variable specific activities tend to have higher specific activities (and therefore more signal); however the volume needs to be calculated each time.
  • Level of proliferation: high specific activity will give more signal, but will be less stable in storage
  • Proliferation vs. probes: Thymidine and methyl thymidine are used for proliferation studies, while thymidine triphosphate is used for probe labeling, because triphosphate is unable to penetrate the cell membrane.
Radiolabeled thymidine table





Typical protocol for CytoStar-T assay

Sample protocol for 384-well CytoStar-T Plate

  1. Grow cells to subconfluence in complete medium. Grow cells at 37°C in a humidified atmosphere with 5% CO2 in 162 cm2 flasks. Passage cells at 1:10. Exponentially growing cells exhibit best uptake.
  2. Release the cells by trypsinization and estimate cell density in the resulting suspension.
  3. Dilute the suspension in complete medium to the selected seeding density and dispense 40 μL/well. Incubate overnight at 37°C, 5% CO2.
  4. Remove overnight media from the wells and wash with 50 μL sterile PBS/well. Dilute [methyl-14C] thymidine to 0.625 μCi/mL in assay medium. Add 80 μL [methyl-14C] thymidine to the wells to give a final concentration of 0.05 μCi/mL.
  5. Add [methyl-14C] thymidine to medium-only for solution control wells (background counts).
  6. Cover the plates with a clear plastic plate seal and count the plates immediately.
  7. Remove plate seal carefully and replace with plate lid. Return counted plate to the incubator. Count plate at appropriate intervals (e.g. every 24 hours up to 72 hours).
  8. Check cells regularly under the microscope for growth and morphology.
  9. Optional: Cells from individual wells may be trypsin released and counted at intervals to determine cell numbers (Cytostar-T signal is cell density dependent).
  10. Optional: At termination of the experiment, uptake may be confirmed by liquid scintillation counting of cells.


Application notes

1. Kivelä, P. et al. Filter counting applications with the MicroBeta2 Microplate Counter. PerkinElmer Application Note (2009). Cell Proliferation Assay on MicroBeta²

2. Härkönen, P.L. et al. Cell Proliferation Assay by Using MicroBeta 3H-Thymidine Incorporation. PerkinElmer Application Note (2001). Cell Proliferation Assay by Using MicroBeta 3H-Thymidine Incorporation



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