Why do medical people use the nonsensical units of % weight per unit volume?

Question

Concentration conventional can be expressed as % by weight, % by volume and weight per unit volume

Answer 1

I would say percent by weight is perfectly valid. The reason they use this is because when it comes to solutions they assume one gram of water is equivalent to 1 ml. Therefore you can put 1 gram into 100mls of water and make a 1% by weight solution. This isn't used as often as you think, certainly medical professionals never use this and refer to weights to volumes directly such as grams per deciliter etc etc. It tends to be restricted to laboratory preperations where absolute precision is not necessary such as when mixing agar gel for electrophoresis where each preparation is measured relative to a control or standard anyway within that preparation. So although its nonsensical to someone unfamiliar with preparations and by pure mathematical standards, it doesn't matter in the lab when precision is not necessary due to standardisation, and when a conversion from volume to weight is known or estimated. It has NOTHING to so with remaining god-like or maintaining professional knowledge as the above poster says.

edit:  No I'm afraid you're talking rubbish. If you find a solution to have 0.02g in 1 litre, you leave it as that; that is the concentration full stop. Its only when you're asked to make a solution for the reasons outlined above and it would be written as "make a 1% agarose solution" and it would NOT be written as 1%g/l (this does not make sense!) Yes, not every solvent used is water but it is in the majority and like I said above, it would only be used when when precision is not necessary and a standard can be used within that preparation for comparison. Other concetration measurements are in micrograms per microliter etc, this is valid. When you deduce concentration you write it as this, when you are asked to make up a solution in the above circumstances you may be asked as "make a 1% solution of agarose" in which case you would put 1gram of agarose in 100ml of water. If you're asked to put something as a percentage of volume, its probably dissolved in water which has a known weight per ml, and the grams of solute which will be known allowing a simple calculation. Please read over both posts again so you understand, as you dont seem to be getting it. By the way, to generalise most medical professions as being poor at chemistry is just plain naive. I'm not going to try to justify this, please explore careers in medicine, in particularly pharmacokinetics , pharmacodynamics, and proteomics,  which extends way beyond the simple concept of weight per volume.

Answer 2

It's a simple convention using % to mean grams per deciliter. And there's no denying that "per centum" means "in the hundred," or that there are a hundred milliliters in a deciliter.

When you say "by definition," it's time to stop and think whether that's the only definition.

Answer 3

the measurement allows one to ignore density.  It isn't nonsensical, chemistry often uses uses volume-based measures (compare molarity and molality as an example).  Depends on how things are sampled and measured, etc.

Answer 4

You are perfectly right of course. From time immemorial the profession has done this, - using archaic or nonsensical units to obfuscate the subject, and confuse the layman. It helps build and preserve the 'god-like' image they like to project, and guard against their knowledge (or lack of it!) being shared or scrutinized.

The other example is the outlandish cod-Greek or Roman names they love to give to perfectly ordinary conditions... so a raised pulse rate becomes "tachycardia" and raised blood sugar level "hyperglycemia"... It saves a lot  of diagnostic work, doesn't it, if you can give something a big, fancy, impressive-sounding name, and send the poor Punter away impressed but untreated?...

The same mind-set has led to the absurdity of so-called "Age-relate Hypertension" with all its attendant ills, - all a complete myth! - But it sells pills, makes the pharmaceutical boys rich, and pays the doctor's kids' school fees..... (Watch and count the 'thumbs-down' votes rolling in from assorted numpties !)

P.S     Oh, - I forgot.. Read this quickly and/or print it out, because within minutes some doctor will have it deleted from Answers probably "for violating Community Guidelines"(!!) by the Answers Gauleiters Polizei

Answer 5

is it to differentiate between %weight per weight?

Answer 6

medical if it does not make sense they called it an art not a science, if it make sense we called it a science. for now lets called it an art. and i don't think you would question why a modern art painting is sold for a million dollar. our doctors are very smart, thats why medical school belongs to faculty of science and art.

forget about math. the reason why grams per liter because the instrument measure the substance weight per liter of blood. (there are about 5 liters of blood in our body), for example glucose, the unit is mg/dL means there are x mg of glucose in y dL of blood.