How to create a (total) Ghrelin calibration curve?

Computing Ghrelin calibration curve using R

The calibration curve can be created using R, and libracy “drc”. Optionally, one can use library “sfmisc” for formatting of the labels on plot axis. The R code is attached below.

The example assumes the data to be available in file “ghrelin_conc std_a std_b avg.csv”

The measured data: {| ! Ghrelin (ng/ml) || Standard a || Standard b |- | 1000000 || -0.040596823 || -0.052699697 |- | 100000 || 0.136105144 || 0.119766263 |- | 10000 || 0.61356354 || 0.606906959 |- | 1000 || 0.846543873 || 0.839887292 |- | 100 || 0.887693646 || 0.88345764 |- | 0 || 0.896770802 || 0.896165658 |}


##### Install libraries
install.packages("drc")
install.packages("sfsmisc")
require(drc)
library(sfsmisc)

##### Read the data
hormone.data <- read.csv("ghrelin_conc std_a std_b avg.csv")
hormone.data <- hormone.data[,1:3]
colnames(hormone.data)[1:3] <- c("Concentration","Response_1", "Response_2")

##### Reorganize the data
hormone.data <- reshape(hormone.data, varying=c("Response_1","Response_2"),  direction="long",  v.names=c("Response"))
hormone.data <- hormone.data[,c("Concentration", "Response")]

##### Fitting the model (4-parameter log-logistic function)
hormone.data.model <- drm(Response ~ Concentration, data = hormone.data, fct =  LL.4())
summary(hormone.data.model)

The calibration curve can be plotted using the commands below:

##### Plotting a nice plot
par(pty="s", mar=c(5,5,1,1))
plot(hormone.data.model, type="confidence", cex.lab=2, axes=F, xlim=c(-10,10^6))
axis(side=1, at=hormone.data[1:6,1], labels=pretty10exp(hormone.data[1:6,1]), cex.axis=1.2)
axis(side=2, at=seq(0,1,0.2), labels=seq(0,1,0.2))
plot(hormone.data.model, type="all", add=T, pch=21, col="red", lwd=1, cex=2, bg="green")


##### Computing the concentration from the response, for instance for a response=0.1, and alpha=1-0.95 ED(hormone.data.model, respLev=0.1, interval=“delta”, type=“absolute”, level=0.95)

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