Osmolality (Urine)

Sample type

Urine (random or 24-hour)

Uses

Assessing the concentrating and diluting ability of the kidney.
Urine osmolality is a measure of the concentration of osmotically active particles, principally sodium, chloride, potassium, and urea; glucose can contribute significantly to the osmolality when present in substantial amounts in urine.
Urinary osmolality corresponds to urine specific gravity in nondisease states.

Precautions

If 24-hour urine is collected, record total urine volume on the request form.
Centrifuge urine sample after collection for five minutes at 4°C to 25°C to remove gross particulate matter.
Some health care practitioners may instruct you to fast (nothing to eat or drink except water) for 6 hours before the test, and/or limit fluids for 12-14 hours before the test.

Interfering factors

Dehydration or overhydration

Heart failure

Liver disease

Kidney disease

Pre-analytical errors

If the sample was not collected with the correct instructions, or you received unlabeled sample.

The corrective action

The sample should be rejected and another sample requested.

If the sample was not collected with the correct instructions, or you received unlabeled sample.

The corrective action

The sample should be rejected and another sample requested.

Post-analytical errors

I. reports were sent to the incorrect patient

The corrective action

communication with patient, apologizing for the error, and providing him with the correct report

II. write the wrong name in the report or the wrong results.

The corrective action

If the report is not delivered to the patient and this error is discovered, the correct result or the correct name must be written, but if the report is delivered to the patient, you must communicate with him, apologies to him, and tell him that an error has occurred and replace it with the correct report.

Reference range

24-hour urine: 300−900 mOsm/kg
Random urine: 50−1400 mOsm/kg
After 12-hour fluid restriction: >850 mOsm/kg