Calculating the EC10 or IC90 values for a dose response curve is not as simple as the EC50 or IC50 values when using the 4PL or 5PL model equations.

The equation for calculating any EC value given a 4PL curve fit is the following:

EC_F = (F/(100-F))^(1/H) * EC₅₀

0 < F < 100 (This is the EC value you are interested in. For example, F=10 for EC₁₀.)
H = Hill Slope for the 4PL curve fit

Luckily, our latest release of MasterPlex ReaderFit 2010 makes this easy. Yes, even with the 5PL curve-fit!

Here’s how:

1. Copy & paste your data into ReaderFit

   Copy your response values from the source and paste it into ReaderFit via CTRL+V -> Paste Response Values.

2. Mark data as Sample Curve type (part 1)

   Select all of the data points that will be used to fit one entire dose response curve including all replicates. In the example given below, there are 7 groups each done in duplicate.
   

3. Mark data as Sample Curve type (part 2)

   Click on the blue Mark Sample Curve button. (The Auto Fill dialog may pop up. Click the Close button if you see it.)
   

4. Indicate known dose concentration values (part 1)

   Select Independent Values(X-axis) from the data pull-down menu. This will show the corresponding data in the plate view. By default, all of the Independent Values(X-axis) will be 0.
   

5. Indicate known dose concentration values (part 2)

   Select the sample of interest and double-click the lower-cell to enter edit mode. Once in edit mode, type in the concentration value. Make sure all values have the same unit. We will edit that later.
   

6. Fitting the curve (part 1)

   Select the Fit Curves tab.
   

7. Fitting the curve (part 2)

   Select either the Four Parameter Logistic (4PL) or Five Parameter Logistic (5PL) from the Curve Fitting section and press the Calculate button.
   

8. Edit dose response curve axes

   Right-click on the dose response curve chart and edit the x and y axes. You also have the option to add a chart title.
   

9. Calculate EC or IC(Anything) value (part 1)

   Press the Statistics Toolbar button.

10. Calculate EC or IC(Anything) value (part 2)

    By default the EC50 and the log EC50 values are calculated for you. If you have an inhibition curve, press the ICxx radio button to switch to IC50 and log IC50 values.
    

11. Calculate EC or IC(Anything) value (part 3)

    If you have an inhibition curve and you are interested in the IC90 calculation, simply select the ICxx radio button and enter “90” into the Percentages section and press the Add button.
    

If you have not done so yet, I would like to invite you to try the free 14-day trial of MasterPlex ReaderFit.

We are pleased to announce the new MasterPlex Tutorial Series:

• MasterPlex EX Tutorial Series
• MasterPlex QT Tutorial Series
• MasterPlex ReaderFit Tutorial Series

Each series guides the user through the entire analysis workflow.

It has been a long awaited item on our todo list and we hope MasterPlex users will find this content useful. Please let us know if you have any requests for “how-to’s” that you would like to see.

The 4 Parameter Logistic or 4PL nonlinear regression model is commonly used for curve-fitting analysis in bioassays or immunoassays such as ELISAs or dose-response curves.

The following is the 4PL model equation where x is the concentration (in the case of ELISA analysis) or the independent value and F(x) would be the response value (e.g. absorbance, OD, response value) or dependent value.

F(x) = ((A-D)/(1+((x/C)^B))) + D

Not surprisingly, the 4PL model equation comprises of 4 parameters:

4 Parameter Logistic Nonlinear Regression Model

1. A = minimum asymptote
   
   In an ELISA assay where you have a standard curve, this can be thought of as the response value at 0 standard concentration.
2. B = Hill slope
   
   The Hill Slope or slope factor refers to the steepness of the curve. It could either be positive or negative. As the absolute value of the Hill slope increases, so does the steepness of the curve.
3. C = inflection point
   
   The inflection point is defined as the point on the curve where the curvature changes direction or signs. This can be better explained if you can imagine the concavity of a sigmoidal curve. The inflection point is where the curve changes from being concave upwards to concave downwards (see picture below).
   

   Inflection point and change in curvature or concavity

4. D = maximum asymptote
   
   In an ELISA assay where you have a standard curve, this can be thought of as the response value for infinite standard concentration.

The following are some key characteristics of the 4PL curve-fit model:

• Symmetry – There is perfect symmetry for the sigmoidal curve around the inflection point for 4PL curve fits.
  
  

  Symmetry around inflection point for 4PL

• Monotonic – A monotonic function is either always increasing or decreasing for all values of x.
  
  

  An example of a monotonic increasing function

  

  An example of a monotonic decreasing function

• Assumptions made by the 4PL model equation
  • It assumes that the standard deviation of the scatter is the same for all values of x (homoscedastic data). In the example of a standard curve, this is saying that the standard deviation for all the replicates of a low standard is equal to the standard deviation of the replicates for your high standard (see example curve below).
    
    

    Homoscedastic Data

    Of course, this is rarely the case when dealing with bioassays or immunoassays (ELISAs) where the data is heteroscedastic. We normally see something like this where the standard deviation increases as x increases:

    

    Heteroscedastic Data

    Applying weighting algorithms for 4PL and 5PL curve fitting is something that can be done to offset the assumption that data is homoscedastic.

  • The 4PL model equation also assumes that the scatters a normal (or Gaussian) distribution.

If you are looking for a curve-fitting software with the 4PL model equation and also does weighting, then try out the Free 14-Day Trial of MasterPlex ReaderFit (fully-functional).

You may also be interested in reading our blog post on:

• 5PL nonlinear regression model
• Tips for ELISA analysis
• The importance of weighting with the 4PL and 5PL
• Dose response analysis and EC₅₀/IC₅₀ determination

We have listened carefully to our customers’ requests and the result: MasterPlex ReaderFit 2010!

This latest version of ReaderFit focuses on making data analysis even easier and more streamlined EC50/IC50 analysis.

Here is a list of what’s new in ReaderFit 2010:

• Easier Data Import
  You can now copy & paste your raw values (e.g. OD, absorbance, fluorescence intensities, etc.) instead of having to use the File Import Wizard.
  
• EC50/IC50 Field Available in Results tab
  The EC50/IC50 values are now available (from 4PL & 5PL curve fits) in the Results for report generation via the Columns Selector.

  

• EC(anything) or IC(anything) Calculation
  Need to calculate the EC90 or IC90 value? The new EC/IC(anything) feature can calculate and report any value you need.

  

• Quality Control Manager with new Upper Limit of Detection (ULOD)
  The Quality Control Manager is now included in every copy of MasterPlex ReaderFit. In addition, we have now added the ULOD to help further refine your results.

  

• Acquire Results with One Click
  Templates can now store curve fitting parameters along with all your plate layout information. With a push of a button, your entire plate layout is loaded (along with your standard information) and your results will be automatically calculated for you.
• More Flexible Curve-Fitting Chart
  You can now customize curve-fitting chart titles and X&Y axes with a simple right-click.

  

Try the Free 14-Day Trial Today!

Are you planning to upgrade from an earlier version of MasterPlex ReaderFit?

Here is a list of features from previous versions:

• MasterPlex ReaderFit v1.1
  • Quality Control Manager (optional in v1.1 but it is built into v2)
  • Step-by-step video tutorials to guide the full analysis workflow
  • Copy and paste Group Names
  • Get at-a-glance views of all points on the standard curve by simply hovering over with your mouse
  • Added compatibility with .xlsx files

We recently had a customer that was interested in MasterPlex QT because his current analysis software for his Bio-Plex instrument was reporting a lot of “OOR < ” or out of range concentration values (below the lower asymptote in this case) for points on the lower end of curve. This is what you would normally expect to see for values that fall below the minimum asymptote BUT the software did not have the capability to use weighting in calculating the lower asymptote which can greatly affect points on the lower part of the curve.
Read the rest of this entry »

Dose response assays are generally characterized by a nonlinear relationship between the response and the amount of drug/agonist/antagonist given. When plotted, this response will usually exhibit a sigmoidal curve that is best described using the 4 Parameter Logistic (4-PL) or 5 Parameter Logistic (5-PL) nonlinear regression model equation.

Dose Response Curve

What’s New in this Upgrade?

• For MasterPlex QT
• For MasterPlex ReaderFit
• For MasterPlex EX

The MasterPlex 21 CFR Part 11 Plug-in has just been released for use with MasterPlex QT v4.0, MasterPlex ReaderFit, and/or MasterPlex EX.

For organizations working under the FDA 21 CFR Part 11 regulations, this plug-in offers:

• Multi-level user account management
• Electronic Signature
• Digital Signature on the digital outputs
• File alteration detection
• Log records
• Audit trail (full log records)
• Seamless connection with the xPONENT Luminex control software
• A unique Finger Vein Identification option (PowerPoint Brochure, Product Page)

Download the FREE Trial version and request a license today!

The following webinar recordings have been made available for viewing at your own leisure:

• What’s New in MasterPlex QT
  View Webinar | PowerPoint Presentation
• Improving your results with MasterPlex QT
  View Webinar | PowerPoint Presentation
• From Genes to Proteins: Multiplex Assays for Studying Gene Regulation and Cell Function with guest presenter, Dr. Jim Lazar, from OriGene Technologies, Inc.
  View Webinar | PowerPoint Presentation
• MasterPlex ReaderFit 101
  View Webinar | PowerPoint Presentation
• The Wait is Over: A New QC Tool for Luminex/Bio-Plex Analysis
  View Webinar | PowerPoint Presentation
• AssayCheX Process Control Panel for Luminex/Bio-Plex Immunoassays
  View Webinar | PowerPoint Presentation
• 10 Tips for MasterPlex QT v4.0 Power Users
  View Webinar | PowerPoint Presentation
• Microplate Reader/Elisa Data Analysis made easy with MasterPlex ReaderFit
  View Webinar | PowerPoint Presentation
• MasterPlex EX: Multiplex Expression Analysis software for Luminex/Bio-Plex data
  View Webinar | PowerPoint Presentation

We have a couple of free webinars coming up that I would like to announce:

• 10 Tips for MasterPlex QT v4.0 Power Users on August 20th at 11AM – 12PM PDT – Reserve your seat!
• Microplate Reader/Elisa Data Analysis made easy with MasterPlex ReaderFit on September 10 at 11:00 AM – 12:00 PM PDT – Reserve your seat!

If you cannot make the time for the MasterPlex ReaderFit webinar, you can view a previously recorded video of it and obtain the PowerPoint presentation slides.

A recording of the MasterPlex QT webinar will be available online after August 20th, 2009.

The MasterPlex ReaderFit webinar covers the basic analysis of an elisa assay. Here is the list of topics that will be discussed in the recording:

1. File Import Wizard
2. Automatic Detection of Outliers
3. Marking Wells and Grouping of Replicates
4. Entering Standard Information
5. Best Fit and Best Fit Parameters
6. Plotting Unknown Data Points on the Standard Curve
7. WYSIWYG Data Table
8. Chart Customization
9. Templates
10. Custom Reports
11. Virtual Plate

Download the PowerPoint Presentation if you would like to follow along with the recording.

Please click here to view the recorded MasterPlex ReaderFit webinar. Be sure to prepare some popcorn as the running time is about 40 minutes. Enjoy the show =)