LV900 titer calculator

SBI Global UltraRapid lentiviral titer kit · qPCR standard curve

Run

The spreadsheet was written for one kit lot. Everything on it is editable here, because the standards’ assigned titers belong to the lot, not to the maths.

appears on the printed sheet
the standards’ assigned titers belong to this lot
Ct. Your threshold — the spreadsheet does not check this. Blank or 0 turns it off
the sheet reports R² and leaves the judgement to you

Standard curve

Ct is fitted against the natural log of the assigned titer, exactly as the sheet does it: SLOPE(Ct, LN(titer)), INTERCEPT, RSQ. Fit ΔCt is the residual, measured minus fitted. The dilution column is a label that prints on the sheet — the spreadsheet never uses it in a formula, and neither does this.

Standard Ct dup 1 Ct dup 2 Ct average Dilution Titer IU/ml Fit ΔCt

Unknown virus samples

Titer = EXP((Ct − b) / m), the sheet’s formula. The dilution factor is instruction 3 on the sheet, which the spreadsheet leaves for you to do by hand — it is applied here only if you set it.

Sample name Ct dup 1 Ct dup 2 Ct average Titer IU/ml × dilution Adjusted titer IU/ml
×10 lysis × ×100 virus, the example on the sheet

Results

Freeze–thaw check against the lot titer

The right-hand scratch area of the spreadsheet compares a measured sample against a stated original titer. That area contradicts itself several ways, so this panel does only the one unambiguous thing, and lists the sheet’s own numbers below rather than adopting any of them.

the figure on the lot certificate; the example here is 1.42e7
uses the adjusted titer from the table above
What the spreadsheet leaves unsettled — read before quoting a number
What this reproduces, cell by cell

Source: the LV900 kit’s own titer-calculation datasheet workbook, sheet Titer Calculator. The yellow cells on that sheet are B5:C8 (standard curve Ct duplicates) and H5:J14 (sample name and Ct duplicates); they are the inputs here too.

  • D5 = AVERAGE(B5:C5) → Ct average. Excel’s AVERAGE ignores an empty cell, so one filled duplicate gives that single value. Reproduced, and flagged as a single replicate.
  • K20 = SLOPE(D5:D8, LN(F5:F8)) → m
  • K21 = INTERCEPT(D5:D8, LN(F5:F8)) → b
  • K22 = RSQ(D5:D8, LN(F5:F8)) → R²
  • K5 = AVERAGE(I5:J5), L5 = EXP((K5 − b) / m) → titer

The worked example this tool ships with is invented, not measured, and is laid out to match that sheet: standard Ct averages 19.860, 23.350, 26.790 and 30.410 against 1e6, 1e5, 1e4 and 1e3 IU/ml give m = −1.5239393370, b = 40.893, R² = 0.99988842, and an example virus at Ct 23.580 gives 85 878.47 IU/ml. Check the tool agrees with those before you clear them.

Instruction 3 on the sheet reads: “Adjust titer if you diluted virus sample for the titer assay and added lysis buffer in Step 2 of protocol. eg. Titer x 10 (lysis dil.) x 100 (virus dil.)”. No cell on the sheet does this. The dilution column here starts at 1, which reproduces the sheet’s printed value, and the button sets 1000 for the sheet’s own example.

Nothing you type leaves your computer. The sheet is stored in this browser only, and a different browser or a different tab address keeps a different copy.