24-Urine Iodine Test Results/ Clarification

[Guest guest]

>Dr. Ain:

>Following up on my posting regarding my recent 24-hr urine iodine

>analysis, the following information was received today. Would you

>be kind enough to review? After a LID of one week, the urine

>specimen was collected and taken to Clinical Pathology Lab in

>Austin, TX. The sample was then prepared and sent to the Mayo

>Clinic in Rochester, MN. The results were as follows:

>Test: 24Hr Urine Iodine

>Iodine Results: 109 Units: UG/SPEC

>Expected Range: 100-460

>Iodine Concentration Results: 58 Units: UG/L

>Expected Range: 42-350

>Urine Volume: 1875 Units: ML

>

>1) Should the UG/SPEC be 80 or less?

>2) Are the Expected Ranges for " normal " individuals?

>3) Curiously, what approx. value of UG/SPEC would one expect

>immediately after a CT Scan?

Dear ThyCa Members:

I do not, as a general rule, give specific medical advice (except to

my own patients); however, to use these publicly-provided results as

a teaching example is fine. The laboratory measured the

concentration of iodine in the urine sample (58 mcg per liter urine).

They were told that the entire 24-hour urine collection specimen

measured 1875 mL or 1.875 liters. Using that information, they

calculated that the entire 24-hour urine specimen contained 109 mcg

(1.875 x 58).

Long experience with the low iodine diet (and experience with urine

iodide studies) shows that, if a patient is compliant with the diet

(a very critical factor and not always dependable), the total 24-hour

urine iodine will be less than 50 mcg. In assessing for residual

iodine from contrast dye studies, if one can assume that the patient

followed the diet perfectly, any iodine in excess of that number

comes from the contrast dye. Theoretically, the lower the

non-radioactive iodine in the body, the more radioactive iodine would

be able to enter any thyroid cancer cells for scanning or treatment;

however, practical issues must be considered. Urine values of 500

mcg or more in 24-hrs (as can be seen on an unrestricted diet or with

contrast dye (despite a low iodine diet) would provide greater

relative interference than values under 100. As a matter of

convention, I've found that values under 100 do not deter me from

proceeding with the scan or therapies, but lower is always better.

Another issue of relevance concerns the seriousness of the thyroid

cancer situation. In patients with widespread metastatic disease and

marginal tumor uptake of iodine or unknown sites of disease with

elevated thyroglobulin levels, even small elevations in the 24-hour

urine iodine may spell the difference between a positive or falsely

negative scan finding and may alter the success of therapy. On the

other hand, patients with small, but highly functional tumors or

remnants (able to avidly take up iodine) may be less affected by the

non-radioactive iodine.

There are no absolutes, only reasonable judgements. For example, if

a patient is planning a follow-up I-131 scan for routine care with no

particular urgency, there is no reason to waste the time and money to

perform such a scan when non-radioactive iodine will render it

suboptimal. Likewise, if metastatic disease has been unresponsive to

prior treatments or only partly responsive, one would not want to be

exposed to high doses of radioactive iodine unless every condition

was optimal for best results. On the other hand, if a CT scan had

been performed with contrast dye prior to surgical removal of the

thyroid cancer, sometimes it is reasonable to proceed with

radioactive iodine treatment, making sure that contrast dye is

avoided for subsequent scanning or therapy.

--

**************PLEASE BE ADVISED*********************

THE INFORMATION CONTAINED IN THIS COMMUNICATION IS INTENDED

FOR EDUCATIONAL PURPOSES ONLY. IT IS NOT INTENDED, NOR SHOULD

IT BE CONSTRUED, AS SPECIFIC MEDICAL ADVICE OR DIRECTIONS. ANY

PERSON VIEWING THIS INFORMATION IS ADVISED TO CONSULT THEIR OWN

PHYSICIAN(S) ABOUT ANY MATTER REGARDING THEIR MEDICAL CARE.

************************************************

B. Ain, M.D.

Professor of Medicine

Director, Thyroid Nodule & Oncology Clinical Service

Director, Thyroid Cancer Research Laboratory

Division of Endocrinology and Molecular Medicine

Department of Internal Medicine, Room MN524

University of Kentucky Medical Center

800 Rose Street, Lexington, Kentucky 40536-0298

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