Jump to content

What are the right Specification Limits for Turn Around Time?

Recommended Posts



DATE: Thu, Jan 8, 2009

Hi all, i have started a six sigma green belt project for reducing turnaround time outliers for serology tests in microbiology lab. Can u tell me how much percentage of sample do i need to take from the population for my study.




Hello friends,

I am doing a Six Sigma project and can u tel me how do i take the specification limits. The project which i am doing says the laboratory follow a turnaround time of giving the reports with in 4 hours. But the time is exceeding to 6 hours in giving the reports. Here should I take the USL as 4 hours or 6 hours. If i take 6 hours as USL then should 4 hours be my target time for calculating the process capability.




Here are some responses that were received to this post:

Your USL must be 4 hours or less. There is no LSL, there can not be any.

Hope this helps.

With warm regards,

Arvind Sinha

IBM India


Hi, G. Vishwanath,

Your OUTPUT : Lab report to be within 4 hrs , currently > 4 hrs ( up to 6 hrs )

The first thing you will have to do is... 1. Analyze your data past 3 months to find out what is current reality. 2. Reason out if there is pattern of delays for particular reporting. 3. Identify Lab reporting categories and further analyze what categories are in time and out of time. 4. Check if there are special causes for specific delays. After doing so, now you are comfortable to realize actions. Pls understand, SIX SIGMA projects are very metodical and robustic in approach, you will have to be very clear in your thinking processes. Further, If the Output with which you have to work is 4 hrs, your control limits should be between 0 on LSL and 3& half hrs to acheive the desired output. ( For this you will have to do a Flow tree path analysis or Critical path method analysis ). Simple would be a Value stream Mapping.

Best Wishes, Sathya TSDO : Quality Program Manager MBB ; E1- LSS ; Certified LA ISO / ISMS


Hi Vishwanath,

4 hrs should be the USL and less than 4 hr should be the target.




Hello Vishwanath,

Spec limits would be what you are supposed to deliver on so in your case your USL will be 4 hours. You will not have an LSL. 6 hours is what the process is delivering. The other question you had is about the target value. Ideally this should be a value well within your spec limit. If you do not have this value leave it blank in Minitab 15,

Thanks and Regards,



Dear Mr. Vishwanth,

I am wg.cdr. (Dr.)Sudhir Ketkar. i am presently assisting two of the hospital laboratory in accreditation by NABL. Firstly specification limits are being given by clients. If you turn around time is within 6 SD from the nearest specification limet, it would mean that the laboratory is working at 6Sigma level. Now first of all, the clients in case of laboratories seldom have specifications except the referring clinicians and that too would depend upon the urgency of the results. No specific requirements are generally provided by the clients. It will also depend upon the nature of the investigations. One can not therefore generalise as in case of microbiology the result may take more than 24 hours and in histopath the result may well take more than 72 hours. Therefore the turnaround time will defer in few investigations. If the project charter says that the turnaroud time be less than 4 hrs and actual time exceeds 6 hrs most of the time the error would have already occured. Since there is no LSL available in this, the project does not naturally fall as a six sigma project. All projects may not be six sigma projects. It may just mean that actually process improvement may be required. you may take statistical data, and also that of a bench mark. and if you are far off the mark, do a fishbone analysis, a pareto analysis may be and try to improve the process. For Mr. Vishwadeep Khatri: I have been out of circulation for quite a while. Kindly correct me if my understanding is wrong. with regards

sudhir ketkar


Dear Sudhir,

I read your post and there are a couple of things i would lilke to clarify for you. 1. If the data is outside spec limit it is not meeting the requirement. I am sure what u meant is that if 99.997% of the data lies within 6SD from the mean and the data is within spec limits then it is six sigma complaint. 2. if the time taken to do a test is 6 hours and the clients want it in 4 hours ( which cannt be done due to the process itself) then the process is not capable and you should have a negative cpk. (This is just a scenario) 3. All six sigma projects do not have to have a LSL and a USL. some of the projects will only have a LSL and others only a USL. In my previous post i have mentioned that use minitab and unavailable spec limt blank. what you may want to do is set a lower boundry which in this case is 0. So here there are 2 approaches one is the old Goal post mentality which say that you have to have all you points within certain spec limits and the other is reduce the variation and move the mean. the first is something which nobody uses any more. In the second option do the following 1. is there variation 2. if the variation is high then map the process and find out what is causing variation. (you might want to look at the 7 M's) 3. once you have adressed variation check wether the process itself can be reduced and move the mean to below 4hrs.

Murali Nair

Director Six Sigma MBB ASQ

Link to post
Share on other sites
  • 2 weeks later...

Hi, as the members said that there is no LSL for the TAT, one thing i would like to share with u all is that, the process for investigations take 2hr for normal reports and if there is any abnormal results the test is repeated and so the TAT will increase. So here in this case can i take USL as 4 hours and LSL as 2 hours. Pls suggest me.

Thanking you all


Link to post
Share on other sites
  • 8 years later...

Dear Vishwanath,


Anything that is outside of the specification limits is a defect. If the customer gets a lab test report sooner than 2 hrs, it will not be a defect. As is mentioned by Mr Nair, not all projects will have an LSL and a USL.


What you have mentioned is what will add to the variation in the TAT.


Let us take another example, if we order a pizza, we expect it to be delivered within 30 min. If it is delayed, that is a defect (as it doesn't meet the customer specified max limit or USL of 30min). However, this will have no LSL as the customer will not complain if the pizza arrives in 5, 10 or 15 min. The sooner it happens the better it is.



Link to post
Share on other sites
  • 1 year later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Who's Online (See full list)

    There are no registered users currently online

  • Forum Statistics

    • Total Topics
    • Total Posts
  • Member Statistics

    • Total Members
    • Most Online

    Newest Member
  • Create New...