If anyone wants to check on whether they might be losing a lot of electrolytes in urine, or just whether their urine is excessively dilute (indicating that they may need some desmo) or excessively concentrated (perhaps indicating that they have had too much desmo/should not take any at the moment) you can estimate your urine osmolality using a brewer's/winemaker's hydrometer (they don't cost much) and a thermometer, and doing some sums, then checking the results against normal ranges which you can find online.
I posted the calculation methods in my blogpost and am copying them below:
1. Measure specific gravity of sample.
2. Take temperature of sample.
3. If sample is above 15.6 degrees C, add 0.001 to specific gravity figure for each 3 degrees above 15.6 degrees C. (e.g. if sample is at 21.6 degrees C, add 0.002.) (Not sure what you do if it is below 15.6 degrees, but if you do measurements soon after urine is produced it shouldn't be!)
4. Multiply by 33194.
5. Subtract 33247.
That should give you the osmolality.
Osmotic particles that increase urine osmolality are commonly the ones in which ME and POTS sufferers are often deficient, notably sodium. I would not be at all surprised if magnesium deficiency were also largely due to urinary loss.
This page has some useful info on urine and serum osmolality, why they are tested and what the tests can tell you.
For normal ranges, labtestsonline are reluctant to specify, but Medline Plus say:
- Random specimen: 50 to 1200 milliosmoles per kilogram (mOsm/kg)
- 12 to 14 hour fluid restriction: Greater than 850 mOsm/kg
However, I would say that if you commonly get a result near the top or bottom of the 'random specimen' ranges that is abnormal. 50 means too dilute and 1200 means too concentrated.
Some sites have a much narrower normal range, e.g.
here:
The normal 24-hour urine osmolality is, on average, 500-800 mOsm/kg of water. Random urine osmolality should average 300-900 mOsm/kg of water.
Without desmo, my urine osmolality was sometimes 100 or less, obviously indicating dehydration due to losing too much fluid in urine. My fluid intake was normal. Later, after I developed hyponatraemia, which doctors misdiagnosed in multiple ways, urine osmo and sodium were quite high compared with those of serum, strongly suggesting the reason for the hyponatraemia, but not proof, as the doc did not order the other tests needed to calculate fractional excretion of sodium (FENa).