{"id":1013,"date":"2014-11-25T20:41:11","date_gmt":"2014-11-25T19:41:11","guid":{"rendered":"http:\/\/stg-blogs.bmj.com\/adc\/?p=1013"},"modified":"2014-11-18T18:12:50","modified_gmt":"2014-11-18T17:12:50","slug":"ignore-the-platelet-count-in-hsp-if-youre-wondering-about-kidneys","status":"publish","type":"post","link":"https:\/\/stg-blogs.bmj.com\/adc\/2014\/11\/25\/ignore-the-platelet-count-in-hsp-if-youre-wondering-about-kidneys\/","title":{"rendered":"Ignore the platelet count in HSP if you’re wondering about kidneys"},"content":{"rendered":"

\"030614_1634_Gamblingalc1.jpg\"<\/a>Every now & then you bump into something that makes your heart sing.<\/p>\n

For me, I sometimes struggle to come up with good examples of an ‘EBM’ tennet – for instance, the difference between statistical and clinical significance – which has an actual origin. Well, in a paper entitled\u00a0Platelet Counts in Children With Henoch\u2013Schonlein Purpura\u2014Relationship to Renal Involvement<\/a>\u00a0I think I have hit gold.<\/p>\n

<\/p>\n

The paper looked at 107 patients with HSP, of whom 28 had renal involvement. A multivariable logistic regression analysis<\/a> showed that platelet count was significantly related to renal involvement (p=0.001). The mean\u00a0counts\u00a0were 483 in the renal group, and 422 in the uninvolved group.This led to an OR<\/a> of 1.0 (1.00 to 1.02) for platelets. They also showed that with the optimal cut point (>565) there was a 36% sensitivity and 49% specificity<\/a> for\u00a0HSP nephritis (I think they got these reversed).<\/p>\n

 <\/p>\n

Yup. Read those numbers again.<\/p>\n

 <\/p>\n

LR+ 1.4, LR-0.7<\/a> — if the\u00a0sensitivity and specificity are indeed written backwards — functionally useless.<\/p>\n

And\u00a0OR of 1.0 (1.00 to 1.02)? (Well actually this is poor presentation of the data — it’s ‘per platelet *10^3’ that this is done in – would make more sense to be for every 10 or 50 increase, wouldn’t it?<\/p>\n

And then add to this the over-optimism of such data cuts<\/a>.<\/p>\n

Like I said. EB-example-gold.<\/p>\n

Just, whatever you don, DON’T use\u00a0platelet count in HSP if you’re wondering about kidneys.<\/p>\n

– Archi<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Every now & then you bump into something that makes your heart sing. For me, I sometimes struggle to come up with good examples of an ‘EBM’ tennet – for instance, the difference between statistical and clinical significance – which has an actual origin. Well, in a paper entitled\u00a0Platelet Counts in Children With Henoch\u2013Schonlein Purpura\u2014Relationship […]<\/p>\n

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