| December 6, 2005 Presentation:
Frontiers In Thyroid Testing |
hello are we ready to go ?
brandon,manitoba,canada
Anthony Butch, PhD:Yes, I am starting to work on the responses in a word document. I will begin cutting and pasting shortly.
What are free hormone estimates
Washington, DC
Anthony Butch, PhD:Free hormone estimates are thyroid hormone assays that do not measure free hormone concentrations directly. Actually, none of the free thyroid hormone assays, including candidate reference methods (free T4 by equilibrium dialysis), actually measure the unbound molecules of thyroid hormone in serum. So in a strict sense, all of the free hormone assays are estimates. However, to avoid confusion, free hormone assays are usually divided into direct methods, indirect methods, and free hormone estimate methods. Direct methods involve the physical separation of free hormone usually by dialysis or ultrafiltration. These assays are not affected by serum binding protein abnormalities or autoantibodies. A sensitive RIA is used to measure free hormone (T4) and the assay is calibrated using gravimetrically determined hormone concentrations. The indirect methods (T4 and T3) add a small amount of radiolabeled hormone and monitor the amount that passes through a membrane, as an indirect measure of free hormone concentration. Free hormone estimate assays rely on antibody binding and include the two-step, and one-step labeled analog and labeled antibody methods. The index methods are also considered estimates of free hormone concentrations.
If a patient has low TSH and clinical symptoms of being hypothyroid, what should one do?
San Diego, CA
Anthony Butch, PhD:Patients with a low TSH should have a free T4 test performed. If the free T4 is normal, a free T3 should be performed to rule-out T3 toxicosis. A low TSH with a normal free T4 and free T3 indicates subclinical hyperthyroidism. This of course assumes that the patient is not on meds that can lower TSH, such as dopamine or glucocorticoids. The case you present is a patient with a low TSH and clinical symptoms of hypothyroidism. Again, a free T4 would be the logical next step. If the free T4 is low, then one would suspect pituitary or hypothalamic dysfunction. A TRH stimulation test could be performed to determine if the cause of the TSH deficiency is of pituitary or hypothalamic origin. However, some institutions (including ours) do not perform this test. Imaging studies would be helpful, as would tests to measure other hormones normally produced by the anterior pituitary.
How long is TSH stable in serum (Vacutainer tubes) at room temp?
Pasadena, CA
Anthony Butch, PhD:TSH is stable in unprocessed serum blood samples (uncentrifuged blood) for at least 6 hours (Clin Chem 44:1325, 1998). A very recent paper published in French indicates that TSH is stable in unprocessed serum samples for 7 hours. An early study found that TSH was stable on the clot for 24 hours when measuring TSH by RIA (Clin Chem 34:2111, 1988). I would be conservative and use a cut-off of 6 hours. If longer times are needed due to long transport times from outlying facilities, I would recommend performing your own stability study.
With our analyzer (using a 3rd generation TSH methodology) the manufacturers recommended normal range is different for international versus US. The US range goes to 6.0 uIU/ml with the international at 3.8 uIU/ml. What would your recomendation be in resolving the gray area between the two upper values?
Viroqua, WI
Anthony Butch, PhD:As routine practice, I do not adopt manufacturers reference intervals without performing our own reference interval study. This is true for almost all analytes, including thyroid function tests. I would recommend that you perform a reference range study to determine the most appropriate reference interval for your patient population. I would look at the results from approximately 140 or so apparently healthy donors without a history of thyroid dysfunction. We often use blood donor samples for this purpose. As an alternative, there are companies that sell ‘normal’ serum samples for about $10 each.
Any thoughts on home test kits for TSH? A number of my patients have come in for follow-up based on home testing, but it seems that the vast majority of these cases are prompted by false posititve results.
Miami, FL
Anthony Butch, PhD:The only home test kit for TSH that I am aware of is the one made by Biosafe. They send you a collection kit in the mail for $40, you add a few drops of blood to the blood transport system and then send the kit back to them for testing. They are CLIA-certified. I was unable to obtain information on how they measure TSH so it is difficult to comment on why you are seeing false positive testing results. There is some information regarding this product at http://www.thyroid-info.com/articles/selftesting.htm. I am not aware of any test kits that can be used by the consumer at home to obtain TSH results.
I am currently on T4 hormone replacement but continue to feel extremely unwell, is there any evidence to suggest that combining T4 T3 treatment is more beneficial?
Cardiff, UK
Anthony Butch, PhD:Almost all of the studies indicate that combination therapy with T4/T3 is not superior to therapy with T4 alone (see Clin Endo 60:750, 2004 & Ann Intern Med 142:412, 2005 as examples). There are exceptions of course. For instance, one study found that combination therapy was superior and improved mood and physical status in some of the participants (N Engl J Med 340:424, 1999). However, the problem with oral liothyronine (T3) is the risk of subclinical hyperthyroidism and impaired well-being due to the fluctuations in steady-state concentrations of serum free T3 due to its half-life. I discussed this with one of our endocrinologists and he indicated to me that he does not use combination T4/T3 unless the patient has significant symptoms of hypothyroidism when adequately treated with T4. In this case the goal is to mimic normal physiology and the patient is given T4 and T3 in a 10:1 ratio (for example, 100 mcg of T4 & 10 mcg of T3).
Our lab director has been telling docs that if a serum TSH screen (case finding) results in a value outside the reference interval that we can reflex to a serum free T4 on the same sample. However, some of the docs want to call the patient back for a redraw. Who's right?
Oklahoma City, OK
Anthony Butch, PhD:I believe that either approach is fine. Of course, a free T4 can be performed off the same sample used to do the TSH testing. This may be appropriate when the patient lives far away or an abnormal result is consistent with the clinical presentation. The main reason why some physicians want a redraw is to confirm that the original abnormal TSH result is correct. It is a good check on the entire process and can help to rule-out preanalytical and analytical artifacts. It also helps interpret slightly increased or decreased initial values given assay imprecision and diurnal/pulsatile secretion of TSH into the blood.
We use the Abbott Architect immunoassay system to run TFT's (TSH, FT4 and total T3). We've had a few inquiries from physicians that are puzzled by results patterns we report that don't seem to fit their clinical impression, or don't fit the diagnosis. ie: patient with funcionally nodular goiter (scan confirmed), and TSH is low, as expected. However on multiple testing events, the Architect assay yielded low-normal or slightly low FT4 results, and normal Total T3. Specimens sent to another laboratory whete TSH was reported similar to ours, but FT4 by dialysis was normal, and Total T3 were elevated. Another patient with toxic MNG yields low TSH, but also low FT4 in our lab. What might explain this?
north hollywood,ca
Anthony Butch, PhD:The thyroid function tests in the first case indicate that the patient has T3 toxicosis due to a toxic nodule. This is based on the low TSH, normal free T4 and elevated T3 (performed by a lab other than yours). Without knowing how elevated the T3 was, it is difficult to determine the problem. If the T3 was only slightly elevated and you obtained a value in the high end of normal than it is possible that your current lot of T3 reagents is exhibiting a negative bias. Have you seen a shift in your QC recently for this assay? Another possibility is that the upper end of your reference interval for T3 is too low. You might want to re-examine the original data and do a reference range study to confirm the interval you are currently using. Heterophile antibodies normally produce high T3 values in competitive immunoassays and would be an unlikely cause of the discrepancy. In the second case are you sure that the results are not correct? A patient with toxic multinodular goiter can have a low TSH and low free T4 during treatment of their hyperthyroidism with thionamides. The low TSH can persist for several months after beginning thionamide therapy.
What is a recommended test menu for Thyroid testing? Obviously, all tests cannot be performed at every institution, but do you have a list of "most important"? If Free T4 is offered, is there any reason to offer Total T4?
Anchorage, Alaska
Anthony Butch, PhD:The most important thyroid tests to offer are TSH with a functional sensitivity less than or equal to 0.02 mU/L, a free T4 assay and a free T3 assay. The two-step free hormone assays are probably the best and are available on automated instruments. Total hormone assays are not necessary if you offer the free hormone assays. Tg, anti-Tg and anti-TPO assays are needed to monitor patients with thyroid carcinoma and thyroditis – these could be sent out if you do not have a busy endocrine service, however, they are all now available on automated instruments.
In the hypothyroid patient on synthroid therapy, what is the free T4 peak level time frame, and is there a recommended time frame to measure the TSH and free T4 from time of medicating?
Boise, Idaho
Anthony Butch, PhD:In patients on levothyroxine (L-T4) replacement therapy for primary hypothyroidism, a serum TSH is adequate to monitor therapy. TSH testing can be performed any time of the day and is not influence by L-T4 ingestion. The optimal TSH therapeutic target is 0.5 to 2.0 mIU/L. Free T4 monitoring is only used in central hypothyroidism, to assess the degree of overtreatment (TSH takes several weeks to re-equilibrate) and to identify non-compliant patients. After ingestion of the usual daily L-T4 dose the free T4 concentration rises with a maximal elevation of 22% above baseline at 3.5 hours and returns to normal by 9 hours (Thyroid 3:81, 1993). Thus when monitoring L-T4 in central hypothyroidism it is important to wait at least 9 hours after dosing.
CAN YOU RECOMMEND A METHOD FOR EVALUATING FUNCTION SENSITIVITY FOR AUTOMATED TSH ASSAYS?
RICHMOND, VIRGINIA
Anthony Butch, PhD:At our laboratory we determine TSH functional sensitivity by starting with a serum pool with a target TSH concentration around 0.16 mIU/L. The pool can be generated by mixing a few patient samples together. The pool is then mixed with another serum pool with an undetectable TSH concentration (hyperthyroid patients), to obtain samples with target values of 0.08, 0.04, 0.02, 0.01, 0.005. All six pools are aliquoted into 10 vials and stored at –70 degrees C. The TSH concentrations and number of pools can be varied depending on individual needs. Each pool is tested for TSH in duplicate on 10 separate days spanning several weeks (twice a week for 5 weeks). The %CV for each pool is determined and the concentration is plotted on the x-axis and the % CV is plotted on the y-axis. A best-fit curve is drawn and the concentration with a CV at 20% is chosen as the cutoff. Values lower than this cutoff are reported as less than the cutoff.
TSH result less than 5mg/dl what does that mean for the patient?
Washington DC
Anthony Butch, PhD:By this question do you mean a TSH less than 5 mIU/L (you wrote 5 mg/dL)? When a TSH is abnormal, either above 4.5 or below 0.45 mIU/L it is recommended that a free T4 test be performed. A free T3 would then be performed if the free T4 is normal and the TSH is less than 0.45. If the thyroid hormone levels are normal and the TSH is abnormal, the diagnosis is subclinical thyroid disease. For TSH levels between 0.1 and 0.45, and between 4.5 and 10, treatment is not recommended. Repeat testing should be performed at 6 –12 month intervals to monitor improvement or worsening in TSH concentrations. Levothyroxine (T4) therapy is recommended for patients with TSH levels higher than 10 mIU/L. Patients with TSH lower than 0.1 mIU/L and no signs or symptoms of hyperthyroidism should be retested within 4 weeks of the initial testing. These guidelines can be found at JAMA 291:228, 2004. These guidelines are controversial as others recommend treatment based on clinical judgement.
(1) Please comment "When should FT4, T4 by direct dialysis RIA methods ?" should be ordered in place of Chemluminescence immunoassays?". With reference to pediatric patients. (2) TSH: A commercial assay with a claimed analytical sensitivity of 0.003 mIU/L and a fuctional sensitivity of 0.015 mIU/L, is this adaquate for pediatric clinicians to make clinical decision?
Los Angeles, Ca
Anthony Butch, PhD:Free T4 by equilibrium dialysis should be requested when the free T4 estimate assay produces results that are not consistent with the clinical presentation or other thyroid tests. This occurs primarily in patients with abnormalities in thyroid hormone binding proteins. A TSH assay with a functional sensitivity of 0.015 mIU/L is adequate for diagnosing thyroid disease in children. However, I would recommend that you confirm the manufacturers claim prior to going-live with the assay by performing your own functional sensitivity study.
You mentioned in your slides the use of TRH stimulation. I was under the impression that TRH is no longer commercially available.
Neptune, NJ
Anthony Butch, PhD:You are correct. TRH is not available any longer in the US. I included the TRH stimulation test it in the presentation because it is discussed in all of the textbooks on thyroid disorders. I will modify the slide and remove ‘rarely performed’ and indicate that TRH is no longer available in the US. I do not know if it is still available in Canada or Europe?
ARE LABORATORIES ROUTINELY REFLEXING FT4 FROM TSH RESULTS?
CORPUS CHRISTI,TEXAS
Anthony Butch, PhD:Some institutions routinely perform a free T4 when the TSH is abnormal. However, I do not know exactly how widespread this practice is. This can be tricky since there are some legal issues involved. At our institution, the physicians decide if they want to ‘add-on’ a free T4 when the TSH is abnormal. We also have a test called TSH with consult. A free T4 is performed when the TSH is abnormal and an interpretive report is included interpreting the test results. If the TSH is low and the free T4 is normal, a free T3 is automatically performed. The TSH with consult is used mostly by family medicine and some of the physicians in our primary care network out in the community.
What are other non thyroidal causes of low TSH?
BRANDON, MANITOBA, CANADA
Anthony Butch, PhD:Non-thyroidal causes for a decreased TSH include: severe illness, long-term nutritional deprivation, drug therapy (dopamine, glucocorticoids, etc.), pregnancy (1st trimester), neuropsychiatric disease, pituitary disease (adenoma), hypothalamic disease, and peripheral resistance to thyroid hormones.
Can TSH values differ depending on the time of day drawn?
University Park, PA
Anthony Butch, PhD:The time of the day that the blood is drawn has minimal effect on TSH levels. TSH secretion is pulsatile, with secretory pulses every two to three hours. However, given the low pulse amplitude and the long half-life of 60 minutes, this produces only modest variations in circulating levels of TSH. TSH also exhibits circadian variations, with peak levels occurring between 2300 and 500 hours. This usually contributes little to variability since TSH testing is normally performed during the daylight hours. In addition reference intervals are usually established on blood samples that are obtained during the daytime.
Diabetic patient (type II) recent significant weight loss, heart palpatation, chills and episodes of rage. Can this be Grave's?
Cleveland, OH
Anthony Butch, PhD:Weight loss, palpitation and emotional lability are symptoms of hyperthyroidism and GravesÂ’ disease, whereas chills are not (heat intolerance and increased sweating are common symptoms). However, these symptoms are relatively common and can be associated with many other disorders. A TSH test should be performed to rule-out primary hyperthyroidism (Graves' disease).
What are the occasions when Thyroid assays should be ordered and done STAT?
Columbus, Ohio
Anthony Butch, PhD:The only circumstances when thyroid tests would be needed on a STAT basis would be in thyrotoxic crisis (thyroid storm) and myxedema coma. In both cases, the diagnosis is made on clinical grounds and emergency treatment is initiated without waiting for confirmatory laboratory test results. The blood sample is normally drawn before initiating treatment. A T4 (either free or total) is usually all that is needed to confirm the diagnosis. Since many laboratories batch thyroid tests and perform testing once a day (our institution), T4 testing in these cases usually ends up being expedited testing (within a few hours) instead of STAT testing. This is usually adequate for treatment decisions.
On slide #28 you refer to NTI. What is NTI
Marquette, Michigan
Anthony Butch, PhD:NTI is the abbreviation for non-thyroidal illness. This is discussed in slides 20 – 24.
On slide #30 you mention analytical and functional sensitivity. How do you differentiate between the two?
Marquette, Michigan
Anthony Butch, PhD:Analytical sensitivity is defined as the lowest concentration of analyte that can be differentiated from a sample containing no analyte. It is commonly determined by measuring the concentration of the analyte in the zero calibrator numerous times (10 – 20) within a single run. The standard deviation is calculated and analytical sensitivity is set at 2 or 3 times the standard deviation. Functional sensitivity is the lowest concentration in a serum sample that can provide a between-run coefficient of variation (standard deviation divided by the mean) less than 20%. Ideally, functional sensitivity should be determined over a several week period using at least two different lots of reagents. Any concentration below this value is reported as less than the limit. Analytical sensitivity is always lower than the functional sensitivity.
Your slides talk to factors that can alter a thyroid function tests pre and post treatment. Once a patient is treated and stabilized on a brand of levothyroxine, could a change in brand or from a brand to a generic be enough to cause the patient's TSH to move out of the normal range?
Chicago, IL
Anthony Butch, PhD:Yes, there can be enough differences between brands of levothyroxine (with the same dosage) to cause the TSH to become abnormal. EndocrinologistÂ’s tell their patients not to switch brands of medication for exactly this reason.
With regards to the stability of TSH, would the use of a serum separator tube prolong the stability?
Chambersburg, PA
Anthony Butch, PhD:Serum separator tubes can prolong the stability of TSH if the tubes are centrifuged. This provides a good barrier that separates the serum from the red blood cell clot. We find that TSH is stable in centrifuged SST tubes for at least 3 days when stored in the refrigerator.
With regards to the stability of TSH, would the use of a serum separator tube prolong the stability?
Chambersburg, PA
Anthony Butch, PhD:Serum separator tubes can prolong the stability of TSH if the tubes are centrifuged. This provides a good barrier that separates the serum from the red blood cell clot. We find that TSH is stable in centrifuged SST tubes for at least 3 days when stored in the refrigerator.
Your slides talk to factors that can alter a thyroid function tests pre and post treatment. Once a patient is treated and stabilized on a brand of levothyroxine, could a change in brand or from a brand to a generic be enough to cause the patient's TSH to move out of the normal range?
Chicago, IL
Anthony Butch, PhD:Yes, there can be enough differences between brands of levothyroxine (with the same dosage) to cause the TSH to become abnormal. EndocrinologistÂ’s tell their patients not to switch brands of medication for exactly this reason.
Do SST tubes have any effect on TSH FT4 and T3 concentrations. How long can these sera sit on the gel prior to testing?
Sunnyvale, Ca
Anthony Butch, PhD:We have not found any differences in thyroid test results using SST tubes on our automated instrument. SST tubes prolong the stability of these analytes if the tubes are centrifuged. This provides a barrier that separates the serum from the red blood cell clot. We find that TSH, T4 and T3 are stable in centrifuged SST tubes for at least 3 days when stored in the refrigerator. However there are some problems with some glass and Plus plastic SST tubes depending on the specific assay used to measure T4 and T3. Please refer to the technical bulletin from BD dated Sept. 23, 2004, the article in Clin Chem 51:424, 2005 and http://www.cap.org/apps/docs/cap_today/feature_stories/0105Tubes.html for additional details.