hyponatremia diagnosis so the diagnosis of hyponatremia is really trivial all you need to do is find a blood test with a sodium less than 135 and you have your diagnosis of hyponatremia but usually what people are talking about when they say what's the diagnosis is what is the ideology what is deriving that low sodium what's the diagnosis behind the low sodium and so we can use an algorithmic approach to get that answer and so if once you have a sodium of 135 you have a diagnosis of hyponatremia then you want to check the serum osmolality okay so if that Serum osmolality is low then you have true hyponatremia if it's normal you have pseudo hyponatremia this is the lab error due to high fats or high proteins in the blood and if you have a high osmolality we have what we were calling factitious hyponatremia where the sodium is truly low but it doesn't have the same implication as a true hyponatremia water is actually moving out of the cells rather than into the cells and this will be due to elevated glucose maybe manitol or maybe a glycine infusion during the Urologic procedure both pseudo hyon treia and factitious hyponatremia make up false hyponatremia indicating that these patients don't have water movement into the cells nor do they show any of the symptoms that are typical for hyponatremia driving down into true hyponatremia the next step is to check the urine osmolality or the urine specific gravity and what we're trying to do is we're trying to determine if there's much ADH activity going on you can think of urine osmolality as being an ADH dipstick if there is low urine ASM mality the lower the more accurate this is you're going to have ADH independent disease okay and so that'll be tea and toast syndrome or beard drink poom Mania these are due to low solute diets and they really respond quite briskly to IV fluids and you want to treat them with a high solute or a high protein diet psychogenic polydipsia these are the patients with compulsive water drinking these patients can be tremendously ill it's a kind of a silly name and it seems like a silly disease but these are the patients that die of hypony and need acute therapy they respond to fluid restriction though if these patient are symptomatic they need to be treated with hypertonic saline and then the renal failure patients these are the patients that are on dialysis or have very very low urine outputs they will have the urine osmoles close to 300 these are kidneys that are so sick they're not able to concentrate or dilute urine and you're going to get urine that's very similar to the cumos mity and these respond to fluid restriction and dialysis treatment moving to the other side of the fence we we have the ADH dependent hypon netas these patients will have high osmolalities and again that higher the osmolality that you've measure on the urine the more accurate this diagnosis is going to be and the step here is you want to check the volume status because that's how we're going to divide these up we have hypervolemic patients with heart failure curosis and nephrotic syndrome we have hypovolemic patients with GI losses renal losses and other losses and we have uvalic patients hypothyroidism adrenalin deficiency and sadh syndrome of inappropriate antidiuretic hormone but this is kind of a fiction because even experts are unable to make an accurate clinical assessment of volume status in more than 50% of cases essentially it's just a coin toss whether you can accurately determine the volume status and so we're really going to rely on a more biochemical assessment here and so you're going to want to measure the urine sodium and the serum uric acid okay and so the hyperic patients they're going to have a urine sodium less than 20 and a high uric acid now it may not be frankly high but it's going to be towards the upper range of normal the hypmic patients will also have a urine sodium less than 20 and a high uric acid or a high normal uric acid and finally the uvalic patients will have a urine sodium greater than 20 and a low uric acid one of the things to be be aware of is that when we say that experts are unable to differentiate volume status we're not saying they can't differentiate hyperic from hypovolemic we are really saying they have a hard time differentiating UIC from hypovolemic or uvalic from hyperemic I don't think people are going to have too much trouble along with clinical background to differentiate between decompensated heart failure and diarrhea but the situations with siadh as part of the differential do become a little bit more tricky some other things to caution you about the urine sodium is not going to be accurate in patients that have recently received diuretics which is probably 100% of patients in heart failure they could have an artificially elevated urine sodium due to the diuretic effect secondly patients with uvalic hyponatremia who are on a very low sodium diet maybe even NPO because they're in the hospital their urine sodium may not be greater than 20 they could have an artificially low urinary sodium that can be a tricky part patients on treatment for gout may have an artificially low uric acid due to treatments with drugs such as alopurinol thanks