<span class="center-menu">← <small>PREVIOUS: [[5.1. Hyperadrenergic POTS]]</small> | <small>NEXT: [[5.3. Neuropathic POTS (associated with small fiber neuropathy)]]</small> →</span> -------- ##### Summary >[!Summary] >**Biomarker** >- (24-hour urinary sodium level <100 mEq/24h)[[#^3]] > >**Details** >- many POTS patients have low blood volumes (a plasma volume deficit of almost 13%)[[#^1]] ; deficit in total blood, plasma and red cell volume[[#^4]] >- patients have inappropriately low levels of standing plasma renin activity and aldosterone compared to normovolemic subjects[[#^2]] >- at least 28.9% were presumably hypovolemic[[#^3]] >- a decrease in oxygenation related to the low red blood cell volume could exacerbate symptoms of orthostatic intolerance[[#^4]] >- POTS patients might have decreased angiotensin II metabolism and that dysregulation by the renin-angiotensin-aldosterone system might contribute to hypovolemia in POTS[[#^5]] -------- >*“Many, but not all, patients with POTS have low blood volumes [14]. Using the [131]-I labeled human serum albumin method, we found that POTS patients had a plasma volume deficit of almost 13%” *<small>([[Raj-2013]], [p. 4](zotero://open-pdf/library/items/CCJLQKRB?page=4&annotation=AF7388CT))</small>^1 >*“Patients with orthostatic tachycardia who were also hypovolemic have inappropriately low levels of standing plasma renin activity and aldosterone compared to normovolemic subjects” *<small>([[Raj-2013]], [p. 4](zotero://open-pdf/library/items/CCJLQKRB?page=4&annotation=SUAGKPWW))</small>^2 >*“at least 28.9% were presumably hypovolemic (24-hour urinary sodium level <100 mEq/24h)” *<small>([[Thieben-2007]], [p. 1](zotero://open-pdf/library/items/5WXWEQWX?page=1&annotation=5GRQNMAT))</small>^3 >*“One of the more consistent findings in patients with POTS is a deficit in total blood, plasma and red cell volume [45;13;46]. Lin has proposed that a decrease in oxygenation related to the low red blood cell volume could exacerbate symptoms of orthostatic intolerance” *<small>([[Garland-2015]], [p. 6](zotero://open-pdf/library/items/CAWTWYLR?page=6&annotation=I38U3XZT))</small>^4 >*“POTS patients might have decreased angiotensin II metabolism and that dysregulation by the renin-angiotensin-aldosterone system might contribute to hypovolemia in POTS” *<small>([[Garland-2015]], [p. 7](zotero://open-pdf/library/items/CAWTWYLR?page=7&annotation=FNXS3FJA))</small>^5