Monthly Archives: February 2016

Flat File Interface your Mass Spectrometer to the Laboratory Information System with R

The Problem

As Clinical Pathologists we work hard to create laboratory developed tests (LDTs) using liquid chromatography and tandem mass spectrometry (LC-MS/MS) that are robust, repeatable, accurate and have a wider dynamic range than commercial immunoassays. In our experience, properly developed LC-MS/MS assays are much less expensive and outperform their commercial immunoassay counterparts from an analytical standpoint.

However, despite mass spectrometry's communal obsession with analytical performance of our LDTs, sometimes we overlook the matter of handling the data we generate. Unlike traditional diagnostic companies (e.g. Siemens, Roche) who take care of upload and download of patient data and results via HL7 streams to the laboratory information system (LIS), mass spectrometry companies have not yet made this a priority. This leaves us either paying out a lot of money for custom middleware solutions or manually transcribing our LC-MS/MS results.

We might naively think, “How bad can the transcription be?” but over time, it becomes painfully evident that manual transcription of result is tedious, error–prone and inefficient use of tech–time.

Many LIS vendors offer what is called a “flat-file interface”. In this case, there is no HL7 stream generated using a communication socket between instrument and LIS. Rather, the results are saved in an ASCII text file with a pre-defined format and then transferred to the LIS via a secure shell (SSH) connection.

For this post, we are going to take some sample flat files from a SCIEX API5000 triple quadrupole mass spectrometer and prepare a flat file for the SunQuest LIS. Please note that this code is provided to you as is under the GNU Public Licence and without any guarantee. You know how all the LC-MS/MS vendors say their instruments are for “research use only”? –yeah, I'm giving this to you in the same spirit. If you use or modify it, you do so at your own risk. Any changes to how your flatfile is generated by your mass spectrometer or any upgrades to your LC-MS/MS software could make this code malfunction. You have been warned.

The Required Format

SunQuest requires the output file to be a comma separated values (CSV) file with a unique specimen or internal QC result in each row. The first column is the instrument ID, the second columns is the specimen container ID (an E followed by a 10–digit integer), the third is testcode and the fourth is the result. The file itself is required to have a time–stamp so that it has a traceable name and should have no header. For an instrument named PAPI (short for Providence API 5000) and a testcode TES (for testosterone), the file might look like this:

The Starting Material

After we have completed an analytical run and reviewed all peaks to generate our fileable results, we can export the quatified sample batch to an ASCII text file. The file contains a whole lot of diagnostic information about the run like which multiple reaction monitoring (MRM) transitions we used, what the internal standard (IS) counts were, results from the quantifier and qualifier ion, fitted values for the calibrators etc. There are more than 80 columns in a typical file and we could talk about all the things we might do with this data but in this case, we are concerned with extracting and preparing the results file.

Dialogue Box

If we are actually going to make an R script usable by a human, it would be good to be able to choose which file we want to process and what test we want to extract using a simple graphical user interface (GUI). There are a number of tools one can use to build GUIs in R but the most rudimentary is TclTk. I have to confess that I find the language constructs for GUI creation both non–intuitive and boring. For this reason, I present without discussion, a modification of a recipe for creating a box with radio–buttons. We are going to choose which of three analytes (you can increase this number as you please) for which we wish to process a flat–file. These are: aldosterone, cortisol and testosterone. Please note that if you execute this code on a Mac, you will have to install XQuartz because Macs don't have native X-windows support despite the BSD Linux heritage of OSX.

This will give us the following pop-up window with radiobuttons in which I have selected testosterone.

dialogue1

You will notice that Tk windows do not appear native to the operating system. We can live with this because we are not shallow.

After you hit the OK button, the Tk widget then puts the chosen value into an Tk variable called rbValue. We can determine the value using the command tclvalue(rbValue). The reason we need to know which analyte we are working with is because the name of the MRM we want to pull out of the flat file is dependent on the analyte of course. We will also need to replace results below the limit of quantitation (LoQ) with “< x”, whatever x happens to be, which will be a different threshold for each analyte.

In our case, the testcodes for aldosterone, cortisol and testosterone are ALD,CORT and TES respectively, the LoQs are 50 pmol/L, 1 nmol/L and 0.05 nmol/L and the MRM names are “Aldo 1”, “Aldo 2”, “Cortisol 1”, “Cortisol 2” and “Testo 1” and “Testo 2” as we defined them within SCIEX Analyst Software. We will use the switch() function to define three variables (test.code, LoQ, and MRM.names) which we will use later to process the flat–file. We will also define the name of the worksheet in a variable called worksheet. These are the parameters you would have to change in order to modify the code for your purposes.

Building File Names

Now we will prompt the user to tell them that they are to choose an instrument flat–file and we will determine the path of the chosen file. We will need the path to both read in the appropriate file but also to write the output later.

This code will create this message box:

dialogue2

and this file choice dialogue box:

dialogue3

and after a file is selected and the Open is pressed, the path to the flat–file is stored in the variable flat.file.path.

Behold: The Data

So we chosen the file we want to read in but what does this file look like? To just get a gander at it, we could open it with Excel and see how it is laid out. But since we have broken up with Excel, we won't do this. SCIEX Analyst exports tab (not comma) delimited files. R has a built in function read.delim() for reading these files but we will quickly discover that read.delim() assumes the files have a rectangular structure, having the same number of columns in each row. R will make assumptions about the shape of the data file based on the first few rows and then try to read it in. In this case, it will fail and you will get gibberish. To get this to work for us we will need to tell R how many rows to skip before the real data starts or we will need to tell R the number of columns the file has (which is not guaranteed to be consistent between versions of vendor software). There are lots of ways to do this but I think the simplest is to use grep().

I did this by reading the file in with no parsing of the tabs using the readLines() function. This function creates a vector for which each successive value is the entire content of the row of the file. I display the first 30 lines of the file. Suppose that we chose a testosterone flat file.

All of the \t's that you see are the tabs in the file which are has read in literally when we use readLines(). We can see that in this file nothing of use happens until line 29 but this is not consistent from file to file so we should not just assume that 29 is always the magic number where the good stuff begins. We can see that the line starting “Sample Name \t Sample ID” is the real starting point so we can determine how many lines to skip by using grep() and prepare for some error–handling with a variable called problem by which we can deal with the circumstance that no approriate starting row is identified.

Now that we know how many lines to skip we can read in the data:

We can have a look at the structure of this file

Just Tell Me the Results

And we see that there is lots of stuff we don't need. What we do need are the columns titled “Sample.Name” (which is the specimen container ID in this case), the “Analyte.Peak.Name” (which is the MRM, either quantifier or qualifier), and the one whose name starts with “Calculated.Concentration..”. The last of these also contains the units of measure which is analyte–dependent. To get rid of this analyte–dependence of the column name, we can find out which column this is and rename it:

Now we can pull out the three columns of interest and put them into a dataframe named results.

Now we only need the quantifier ion results which we were defined by the user with Tk GUI, so we can pull them out with grep. I will pull out the qualifiers also but we do not need them unless we wanted to compute ion-ratios, for example.

Having pulled out the MRM of interest, we can define which rows correspond to standards, QC and patients by appropriate use of grep(). It happens that the CIDs all start with E followed by a 10 digit number so we can search for this pattern with a simple regular expression. Since we only need the QCs and patient data, the variable standards is calculated only as a matter of completeness.

Preparing Data for Output

Now we can prepare to write a dataframe corresponding to the required format of the output file. To do so, we'll need to find out how many rows we are writing and then prepare a vector of the same length repeating the name of the worksheet and testcode:

Now we can replace all the NA values that replaced “No Peak” with the correct LoQ according to which analyte we are looking at.

Our final.output.data dataframe looks like it behaved properly.

Timestamping, Writing and Archiving

And finally, we create directories to archive our data (if those directories do not exist) and write the files with an appropriate timestamp determined using Sys.time(). Since colons (i.e : ) don't play nice in all operating systems as filenames, we can use gsub() to get rid of them. We also pass along error messages or confirmation messages to the user as appropriate.

Finally, we would wrap all of the directory–creation and file–operation in an if statement tied to the variable called problem we created previously. You will see this in the final source–code linked below.

Other Things You Can Do

Now, you can easily modify this to deal with multiple anlytes that are always on the same run, such as Vitamin D2 and Vitamin D3. If you wanted to suppress results failing ion ratio criteria (which could be concentration–dependent of course) or if you had specimens unexpectedly low IS counts, you could easily censor them to prevent their upload and then review them manually. You could also append canned comments to your results with a dash between your result and the comment. In fact, you could theoretically develop very elaborate middleware for QC evaluation and interpretation. You could also use RMarkdown to generate PDF reports for the run which could include calibration curve plots, plots of quantifier results vs qualifier results, and results that fail various criteria.

Source

You can download the source code and three example flat files here. Setting the source–code up as a “clickable” script is somewhat dependent on the operating system you are working on. Since most of you will be on a windows system you can follow this tutorial. You can also use a windows batch file to call your script.

Final Thought

Now that your file is generated, it is read to upload via ssh. This is usually performed manually but could be automated. Don't implement this code into routine use unless you know what you are doing and you have tested it extensively. By using and/or modifying it, you become entirely responsible for its correct operation. Excel is like a butter knife and R is like Swiss Army Knife. You must be careful with it because…

From everyone who has been given much, much will be demanded; and from the one who has been entrusted with much, much more will be asked.

Luke 12:48

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