A recent article includes a cameo appearance by none other than ParameterZ.com:
Method 5: z-scores of LVM indexed for height2.7 were calculated as described in a recent publication which is accessed using an online calculator at http://parameterz.blogspot.com/2008/09/lv-mass-z-scores.html (accessed 6 April 2009).
- Incidence of left ventricular hypertrophy in children with kidney disease: impact of method of indexation of left ventricular mass.
- Simpson JM, Savis A, Rawlins D, Qureshi S, Sinha MD.
- Eur J Echocardiogr. 2009 Dec 15.
Unfortunately, the citation is not quite correct. The attribution is for “z-scores of LVM indexed for height2.7" and, well, they are not. The z-scores are LV mass for height, to be sure, but not indexed for height. The authors assure me this was an error on their part and are going to issue a correction. The conclusions of their study remain unaffected by the mis-wording: different methods of indexation have a profound influence on the categorization of children with respect to LVH.
The term “indexed” in this sense is fraught with misconception. If a measurement is found to be related to body size and an adjustment for body size is attempted- in any form- some are likely to simplify the adjustment by describing the relationship as being indexed to [insert body size parameter here]. Other interpretations are (correctly) more literal, taking the term indexed to mean divided by [insert body size parameter here]. (Further adding to the confusion is the use of the term index in programming jargon to mean “position within an array”, the use of which I am certainly guilty of in the course of explaining how the calculators work).
Adding to this particular variety of confusion is the recent work of one of the co-authors of the Foster et al., work wherein they reverse their previous position and go ahead and officially index LVM/height2.7 but further correct for age (which in its own way seems to correct for height i.e., very few babies are tall). Even more frustration is going to get heaped on the “don’t index stuff” camp by this upcoming JASE article: Predicting Heart Failure Hospitalization and Mortality by Quantitative Echocardiography: Is Body Surface Area the Indexing Method of Choice? The Heart and Soul Study.
I don’t intend to settle this debate. All I am doing with ParameterZ.com is trying to make the information accessible and building some programming skillz in the process. All I can say is read the disclaimer and take it to heart— I do.
All calculations must be confirmed before clinical use or diagnostic purposes by qualified medical professionals.
