MRI/CT-calculated Total Kidney Volume

Total kidney volume (TKV) is a strong predictor of future renal insufficiency in ADPKD.1 Various imaging modalities (MRI, CT, US) and post processing methods (stereology and ellipsoid calculations) are available to determine TKV.1,2

Once TKV has been calculated, it can be used to assess the risk of ADPKD progression in Typical (Class 1) patients, more specifically by estimating TKV growth and eGFR decline over time. This method can be useful in assessing younger patients who may still have normal eGFR levels. Atypical (Class 2) patients should be excluded.2,3

View a hypothetical patient sample calculation or enter practice values to
learn how to measure TKV to assess disease progression:

How to Measure TKV using MRI or CT images and the ellipsoid volume equation

Determining TKV by stereology can be time-consuming and depends on specialized software that is not available to all clinicians. Estimation of TKV by the ellipsoid volume equation (shown below) requires only a few minutes and has sufficient precision to substitute stereology in the classification assignment.2,3

The ellipsoid volume equation uses length, width, and depth measurements determined from the sagittal, coronal and transverse views of an MRI or CT scan.*3,4

Sagittal View

Sagittal View

Coronal View

Coronal View

Transverse View

Transverse View

* Imaging services such as MRI or CT may not be available in all cases. Radiologists may take a different approach than the example provided to determine kidney length, width and depth measurements from MRI or CT scans.

Patient B's kidney dimensions:
Left Kidney

*Length. The length can be obtained by averaging the maximum longitudinal diameters taken from coronal and sagittal images. Alternatively, a single, longitudinal diameter measurement can be obtained from a tilted coronal image.3,4

Width and depth. Use the width and depth of the kidney obtained from transverse images at the maximum transverse diameter.3

Start with the
basic formula:
6
Left Kidney( LLxWLxDL )
+
6
Right Kidney( LRxWRxDR )
=  TKV
Insert the
kidney values:
6
Left Kidney(
130 mm
x
67 mm
x
46 mm
)
+
6
Right Kidney(
127 mm
x
71 mm
x
50 mm
)
=  TKV
Do the math:
Left Kidney
209,785 mm3
+
Right Kidney
236,065 mm3
=  TKV
Convert to mL
for final volume:*
Left Kidney Volume
209.8 mL
+
Right Kidney Volume
236.1 mL
=  
TKV
445.9 mL
*Unit conversion: 1,000 mm3 = 1 mL

How to Use TKV to Assess Risk for ADPKD Progression

With height-adjusted TKV (htTKV), you can see Patient B's classification for annual kidney growth and risk for eGFR decline.3

Start with the
basic formula:
TKVheight
=  htTKV
Enter height
and calculate:
445.9 mL
1.70 m
=  
htTKV
262.3 mL/m

ADPKD Imaging Classification by htTKV and Age*

Classification Chart
Classification Chart Angela

Patient Classifications*

CLASSESTIMATED KIDNEY GROWTH RATE YEARLY % INCREASERISK FOR eGFR DECLINE
1E>6%High Risk
1D4.5% - 6%High Risk
1C3% - 4.5%High Risk
1B1.5% - 3%Intermediate Risk
1A<1.5%Low Risk

Adapted with permission of The American Society of Nephrology, from Irazabal MV, et al. Imaging classification of autosomal polycystic kidney disease: a simple model for selecting patients for clinical trials. J Am Soc Nephrol. 2015;26(1):160-172.

Patient B is likely at low risk for rapid progression.

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