In looking at Lab Corp’s website, where the test was done, I’m guessing that basically the reference range is the same for random as for 24 hr test. But I’m sure that Carol is right that the 24 hr test is the most accurate. But when the test is done, just a sampling of the 24 hr collection is used and they project from that what the amount of sodium would be in 24 hrs. I think this because the instructions for the 24 hr test mentions just a small amount (1 ml) as the minimum for this test. So for a random test, they would project the same way, but it wouldn’t be as accurate.

Lab Corp’s ref. range is 40-220, but they include this info:
"In cases of hyponatremia, urine sodium <10 mmol/L may indicate extrarenal depletion: dehydration (gastrointestinal or sweat loss), congestive heart failure, liver disease or nephrotic syndromes.

Urine sodium >10 mmol/L may indicate diuretics, emesis, intrinsic renal diseases, Addison disease, hypothyroidism, or syndrome of inappropriate antidiuretic hormone (SIADH). In hypothyroidism and in SIADH, Na+ and Cl- may be >40 mmol/L. (Depending on intake, such results also can be found in normal individuals.) In SIADH, urinary sodium is usually >20 mmol/L. Inappropriate secretion of antidiuretic hormone (SIADH) was found in 7% of 250 patients with small cell lung cancer. Such patients have hyponatremia, often severe, with hypo-osmolar serum, high urinary sodium excretion with urine osmolality greater than that of serum. Acute and subacute diseases of the CNS, TB and other chronic pulmonary diseases may also cause SIADH. SIADH may also be caused by acute intermittent porphyria, LE, occasional malignant neoplasms other than small cell carcinoma of lung, and a number of drugs."

I don’t really understand the above because they are talking about levels that are well within their normal range. My daughter’s blood sodium was just below normal (134), which I’ve read is considered hyponatremia. Her osmolality was also low (266, with ref range of 275-300). And her urine sodium level was 190, which is within their normal range, but pretty high (urinary osmolality wasn’t checked). But the endo is not concerned about any of this and says it’s all normal. Any comments?

P.S. Megan: Please look down a bit on the LOCAH page to see other discussion of my daughter’s most recent lab results.

Thanks!