Measured free thyroxine concentrations in serum increase markedly after intravenous heparin administration, but the effect of heparin administered subcutaneously has not been adequately documented. We found in vitro increases of up to 63% in measured FT4 after a single dose of subcutaneous heparin (enoxaparin, 2000 units) in nine healthy volunteers, and the magnitude of these increases was correlated with initial serum triglyceride concentrations (r = 0.93, P <0.005) and in vitro free fatty acid release (r = 0.88, P <0.005). In 10 cardiac inpatients receiving repeated doses of enoxaparin (2000 units twice daily), measured FT4 increased by up to 171% in specimens taken 2–6 h after injection. When specimens were obtained 10 h after injection, the effect appeared to be minimized, with in vitro increases of <40%, but such increases may still be sufficient to cause interpretative errors. If FT4 estimation is absolutely necessary in patients receiving enoxaparin, specimens should be taken ≥10 h postdose and analyzed within 24 h.
Impaired NO-mediated pulmonary vasodilatation does not appear to contribute to exercise limitation in CCF. Alternatively, the lower NO production observed during maximal exercise in the patient group compared with controls may reflect a reduced incremental response of a system that is already abnormally activated in heart failure.
(n = 10). Each patient's series of serum aliquots was thawed and assayed in triplicate in one assay run with dilution in zero standard for samples with free {j-hCG greater than 50 lUlL.
RESULTSOur results (Table 1 and Fig. 1) showed that the free (j-hCG concentration increased significantly when samples were left unseparated for 6 h or more. An average increase of 14% over basal levels was seen at 24 h with the rise reaching 43% for 4-day-old specimens. Such artefactual increases could lead to significant errors in reported Blood samples were collected from informed pregnant women attending a routine out-patient clinic, and each specimen was ali quoted into six plain glass bottles and allowed to clot. The first aliquot was centrifuged after 30 min and the serum was separated and stored at -20 D C . The remaining samples were left to stand at room temperature for 6, 24, 48, 72 or 96 h after the time of collection before centrifugation and freezing of the serum.Serum free {j-hCG was measured by a commercial solid phase two-site immunoradiometric assay [CIS (UK) Ltd, High Wycombe, UK]. The working range of the assay is 0'1-50,0 lUlL and the intra-assay coefficient of variation was found to be 5' 60/0 at a mean value of 0·79 lUlL (n = 6) and 2·3% at a mean value of 29·3 lUlL SUBJECTS AND METHODS Measurement of the free {j-subunit of human chorionic gonadotrophin (hCG) rather than the total or intact hormone in serum has recently been employed as a tumour marker,I as a prognostic indicator in in vitro fertilization programmesand as a maternal serum marker in prenatal screening for Down's syndrome.t? In 1991 Knight and Cole" suggested that serum free {j-hCG levels can rise due to slow dissociation of hCG in 'poorly stored samples of pregnancy serum', but few publications have adequately documented this phenomenon.To assess the suitability of maternal blood samples posted from general practitioners to this laboratory as part of a prenatal screening programme for Down's syndrome, we have investigated the stability of free {j-hCG concentrations in blood samples left unseparated for various lengths of time.
Additional key phrases: prenatal screening; Down's syndrome; tumour markerCorrespondence: Mr Brian Sheridan.
McArdle's disease (myophosphorylase deficiency) results in the inability to metabolise skeletal muscle glycogen to lactate. A patient with this condition developed angina and therefore offered a unique opportunity to explore the differential expression of the defective myophosphorylase gene in skeletal and cardiac muscle.
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