Written by Judith Buckland MBA, RDCS, FASE

### How to Calculate Echo Reference Ranges

We are frequently asked how to calculate abnormal cut-off values for echo measurements based on the standard deviation displayed on the different guideline papers.  How do we use standard deviation to calculate normal reference ranges? This week we will demonstrate how to interpret the echo reference ranges provided by the American Society of Echocardiography and teach you how to quickly calculate echo abnormal values using standard deviation.

## Standard Deviation

Standard deviation is a calculation used to quantify the amount of variation a specific set of values have.  The latest chamber quantification guidelines provides reference ranges on severity only for the left ventricular size, function, mass and left atrial volume. For all other parameters, only the mean value and the standard deviation is provided.

So, how do you read these values and interpret them into normal/abnormal values for your lab?

# How to Calculate Echo Reference Ranges

For all measurements (other than LV size, function, mass and LA volume) the guideline paper only provides us with the mean value and the standard deviation of gender, age and body surface area (BSA). You will see this reported as a number plus/minus the standard deviation.  For example: the Sinuses of Valsalva aorta measurement for men is reported as “3.4 + 0.3 cm”.  Then why is it we post blogs stating the cut-off range for the Sinuses of Valsalva for men is 4.0cm?  How are we utilizing the mean values and the standard deviation range to provide cut-off values?

I wish I could take credit for this, but a smart and patient physician explained this to me!

• The guideline paper states that any parameter exceeding 1.96 of the standard deviation should be classified as abnormal.
• To make this easy to apply in real life you can round the 1.96 up to 2.
• To calculate the abnormal cut-off value for any measurement provided in the guideline paper, the standard deviation has to be multiplied by TWO!

# Example

The guideline paper can help you determine if the value is normal or abnormal but in regards to specifying what degree of abnormal (mild, moderate or severe), that remains at the discretion of your lab.  The writing group for the ASE guideline paper does not recommend specific values for severity.

## Summary

Judith Buckland, MBA, RDCS, FASE

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## LET US KNOW WHAT YOU THINK...

Chinh Pham Trung
Thank you so much for clarifying, i have been doing wrong for longtime .Instead of multiplying by two the deviation standard , i only minus or plus the deviation standard !
Ritza Driver
Thank you, I have been doing exactly the same as Chinh Pham Trung. Thank you for sharing
Chinh Pham Trung
In order to obtain good images , we should have minimal knowledge about technical aspect of the equipment . Sometime i dont know when i have to use a low wall filter , how to modify TGC , gain , volume sample. I hope you can help us to understand it better

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