Nephrotic syndrome - Friday April 13, 2012

Thank you to Dr. E. Cole for hosting a special nephrology morning report and to team 6 for bringing the case.

We discussed a patient with known nephrotic syndrome (heavy proteinuria) and presented with renal vein thrombosis.  We discussed that other than the usual signs and symptoms of nephrotic syndrome, two complications are frequent infections and thrombosis.  We also discussed the differential diagnosis of edema from a pathophysiologic point of view.  The 3 mechanisms or increased hydrostatic pressure, decreased oncotic pressure, and increased capillary vessel permeability.  Some disease processes that increase hydrostatic pressure include heart failure, volume overload secondary to renal failure, DVT, obstructed lymphatics, or portal hypertension from liver disease.  Some disease processes that decrease oncotic pressure include decreased albumin synthesis from liver disease, nephrotic syndrome (losing protein), or protein-losing enteropathy.  Capillary vessel permeability is sometimes secondary to trauma or inflammation.

For Amuse Bouche, we posed of question of calculating the post-test probability given the likelihood ratio and pre-test probability.  The pre-test probability given was 20%, and the positive likelihood ratio was 16.  To do this, we:

1.  Convert the pre-test probability to pre-test odd.

2.  Multipley the pre-test odd with the likelihood ratio to obtain the post-test odd.

3.  Covert the post-test odd to post-test probability.

In our case:

1.  Pre-test odd = pre-test probability / (1 – pre-test probability).  In our case, this is 0.2/0.8 = 0.25.

2.  Then we get post-test odd = pre-test odd X LR = 0.25 x 16 = 4.

3.  Then we get post-test probability from post-test odds by this formula:  probability = odds / (1 + odds).  In this case, post-test probability = 4/(1+4) = 0.8.

Therefore, the post-test probability is 80%.