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Continuing evaluation of a routine thyroid profile
254
THE A U S T R A L I A N ASSOCIATION OF BIOCHEMISTS
Pathology (1975),7, July
Quality control of the kits has proved adequate with little variation. However 4% of the tests showed unacceptable replicates, in our hands, and warrants testing in duplicate. In comparison to previous tests used, there is increased sensitivity at the lower level but a slight decrease in the hyperthyroid range. As part of our evaluation of ETR, estimations were performed on 202 consecutive patients from the Nuclear Medical Thyroid Unit. Clinical diagnosis and ETR agreed in the 175 definite cases. TSH and T3 helped to separate the 27 borderline cases. A homemade ETR-like technique has been developed to reduce the cost of the test.
CONTINUING EVALUATION OF A ROUTINE THYROID PROFILE GEARY, T. D., PAIN,R. W., PHILCOX, J. and DUNCAN,B. M . Institute of Medical and Veterinary Science, Adelaide, South Australia
The Mallinckrodt ETR is the basic screen in our thyroid function profile. TSH or T3 measurements are automatically performed if the ETR value falls in the high or low overlap areas which include the third S D of normals. The validity of the low area was checked by measuring TSH levels in sera from 202 consecutive patients passing through the Nuclear Medical Thyroid Unit and 110 cases from our routine department with ETR values falling in or below the overlap area. Experience would indicate that TSH values below 20 mu/l in primary and 30 mu/l in iatrogenic hypothyroidism d o not require replacement unless clinically indicated. Our results show that ETR alone may be a good indicator of replacement for if the ETR is above 0.99 the TSH level is in the reference range. The upper overlap area is difficult to assess due to possible alteration in binding proteins. However in the above 202 patients there were 13 cases with borderline results, 6 had normal; 2 were borderline and 5 had elevated T3 concentrations.
TRIIODOTHYRONINE RADIOIMMUNOASSAY I N UNEXTRACTED SERUM KANAGASABAPATHY, A. S., WELLBY,M. L. and MARSHALL, J. Department of Clinical Chemistry, The Queen Elizabeth Hospital, Woodville, South Australia
A radioimmunoassay (RIA) has been developed for serum T3, utilizing a highly specific T3 antiserum derived from rabbits immunized with T3-bovine serum albumin conjugate. Merthiolate is included to inhibit T3 binding to TBG, but T3-antibody binding is also inhibited, leading to insensitivity and spuriously high values. Inclusion of T3-free serum restores T3-antibody binding. The antigen-antibody mixture is incubated overnight at 4 C and free and bound fractions are separated using dextran-coated charcoal. The sensitivity of the assay is 15 ng/100 ml serum. Within assay precision and between assay precision are 5.9% and 8.9% respectively. The overall recovery is 99+ 8% (mean SEM). The reference range (mean+ 2 SD) foreuthyroidsubjects is84-188 ng/IOOml. lnuntreated thyroroxicpatientsanoverallrangeof200-1863 ng/IOOml has been found, similarly primary myxoedema 0-100 ng/100 ml, and euthyroid females on oral contraception 116-250 ng/100 ml. The main application of T3 RIA has been in investigation of patients with treated thyroid disorders, particularly those with thyrotoxicosis treated with radioactive iodine in whom a preferential secretion of T3 has been demonstrated.
EUTECTICS: A NEGLECTED AREA IN CLINICAL CHEMISTRY PAIN,R. W., PHILCOX, J. and DUNCAN.B. M . Institute of Medical and Veterinary Science, Adelaide, South Australia When serum is cooled in the deep freeze, ice crystals of pure water form progressively. The progressive removal of water leads to increasing concentrations of salts and proteins in the residual unfrozen solution. This continues until the eutectic point for serum is reached (-23°C) at which point the remaining water, salts and proteins solidify together as an eutectic mixture. Thus at -20°C small lakes of a liquid concentrate of proteins in hypertonic salt solution exist inside a solid matrix of water ice. Under such circumstances denaturation of proteins may occur especially as the p H may fall to as low as 3. Accordingly -20°C may be about the worst temperature a t which to store serum, a t least for some substances.lt may therefore be advisable to use-70'C refrigerators for storage of sera for susceprible substances such as clotting factor standards and controls.
THE A U S T R A L I A N ASSOCIATION OF BIOCHEMISTS
Pathology (1975),7, July
Quality control of the kits has proved adequate with little variation. However 4% of the tests showed unacceptable replicates, in our hands, and warrants testing in duplicate. In comparison to previous tests used, there is increased sensitivity at the lower level but a slight decrease in the hyperthyroid range. As part of our evaluation of ETR, estimations were performed on 202 consecutive patients from the Nuclear Medical Thyroid Unit. Clinical diagnosis and ETR agreed in the 175 definite cases. TSH and T3 helped to separate the 27 borderline cases. A homemade ETR-like technique has been developed to reduce the cost of the test.
CONTINUING EVALUATION OF A ROUTINE THYROID PROFILE GEARY, T. D., PAIN,R. W., PHILCOX, J. and DUNCAN,B. M . Institute of Medical and Veterinary Science, Adelaide, South Australia
The Mallinckrodt ETR is the basic screen in our thyroid function profile. TSH or T3 measurements are automatically performed if the ETR value falls in the high or low overlap areas which include the third S D of normals. The validity of the low area was checked by measuring TSH levels in sera from 202 consecutive patients passing through the Nuclear Medical Thyroid Unit and 110 cases from our routine department with ETR values falling in or below the overlap area. Experience would indicate that TSH values below 20 mu/l in primary and 30 mu/l in iatrogenic hypothyroidism d o not require replacement unless clinically indicated. Our results show that ETR alone may be a good indicator of replacement for if the ETR is above 0.99 the TSH level is in the reference range. The upper overlap area is difficult to assess due to possible alteration in binding proteins. However in the above 202 patients there were 13 cases with borderline results, 6 had normal; 2 were borderline and 5 had elevated T3 concentrations.
TRIIODOTHYRONINE RADIOIMMUNOASSAY I N UNEXTRACTED SERUM KANAGASABAPATHY, A. S., WELLBY,M. L. and MARSHALL, J. Department of Clinical Chemistry, The Queen Elizabeth Hospital, Woodville, South Australia
A radioimmunoassay (RIA) has been developed for serum T3, utilizing a highly specific T3 antiserum derived from rabbits immunized with T3-bovine serum albumin conjugate. Merthiolate is included to inhibit T3 binding to TBG, but T3-antibody binding is also inhibited, leading to insensitivity and spuriously high values. Inclusion of T3-free serum restores T3-antibody binding. The antigen-antibody mixture is incubated overnight at 4 C and free and bound fractions are separated using dextran-coated charcoal. The sensitivity of the assay is 15 ng/100 ml serum. Within assay precision and between assay precision are 5.9% and 8.9% respectively. The overall recovery is 99+ 8% (mean SEM). The reference range (mean+ 2 SD) foreuthyroidsubjects is84-188 ng/IOOml. lnuntreated thyroroxicpatientsanoverallrangeof200-1863 ng/IOOml has been found, similarly primary myxoedema 0-100 ng/100 ml, and euthyroid females on oral contraception 116-250 ng/100 ml. The main application of T3 RIA has been in investigation of patients with treated thyroid disorders, particularly those with thyrotoxicosis treated with radioactive iodine in whom a preferential secretion of T3 has been demonstrated.
EUTECTICS: A NEGLECTED AREA IN CLINICAL CHEMISTRY PAIN,R. W., PHILCOX, J. and DUNCAN.B. M . Institute of Medical and Veterinary Science, Adelaide, South Australia When serum is cooled in the deep freeze, ice crystals of pure water form progressively. The progressive removal of water leads to increasing concentrations of salts and proteins in the residual unfrozen solution. This continues until the eutectic point for serum is reached (-23°C) at which point the remaining water, salts and proteins solidify together as an eutectic mixture. Thus at -20°C small lakes of a liquid concentrate of proteins in hypertonic salt solution exist inside a solid matrix of water ice. Under such circumstances denaturation of proteins may occur especially as the p H may fall to as low as 3. Accordingly -20°C may be about the worst temperature a t which to store serum, a t least for some substances.lt may therefore be advisable to use-70'C refrigerators for storage of sera for susceprible substances such as clotting factor standards and controls.