Price R I, Kent G N, Rosman K J, Gutteridge D H, Reeve J, Allen J P, Stuckey B G, Smith M, Guelfi G, Hickling C J
Department of Endocrinology & Diabetes, Sir Charles Gairdner Hospital, Perth, Western Australia.
Biomed Environ Mass Spectrom. 1990 Jun;19(6):353-9. doi: 10.1002/bms.1200190605.
Oral (44Ca: 0.13-0.20 mmol) and intravenous (42Ca: 0.02-0.037 mmol) isotopically enriched stable calcium (Ca) tracers were given together with an oral dose of 2.5 mmol of natural Ca to normal subjects. Blood and urine samples were collected up to 24 h after the tracer doses and atom fractions (AFs) of these tracers (relative to natural Ca) were measured by high-precision thermal ionization mass spectrometry (TIMS). The time-dependent fractional rate of oral dose absorbed and true fractional intestinal Ca absorption (alpha) were derived from the Afs by mathematical deconvolution. After 6 h, the ratio AF oral tracer/AF intravenous tracer in blood equalled that in urine and did not change thereafter. Reproducibility of the combination of chemical precipitation of Ca (from a urine standard) and subsequent TIMS measurements, in nine runs over 13 months, was 1.2% (coefficient of variation). This was in accord with the within-run reproducibility. An estimate of alpha derived from a single blood or urine measurement was 6-10% higher than the reference value obtained by deconvolution. This discrepancy could be explained by a correction factor depending, in part, on the elapsed time for peak Ca intestinal absorption rate. Instrumentally induced mass fractionation, as well as contributions from radiogenic Ca, had a significant effect on the accuracy and reproducibility of the ratio of AFs of tracers in blood and urine.
向正常受试者口服（44Ca：0.13 - 0.20 mmol）和静脉注射（42Ca：0.02 - 0.037 mmol）同位素富集的稳定钙（Ca）示踪剂，并同时口服2.5 mmol天然钙。在给予示踪剂剂量后的24小时内采集血液和尿液样本，并通过高精度热电离质谱法（TIMS）测量这些示踪剂的原子分数（AFs，相对于天然钙）。口服剂量吸收的时间依赖性分数率和真实的肠道钙分数吸收（α）通过数学反卷积从AFs中推导得出。6小时后，血液中口服示踪剂的AF/静脉注射示踪剂的AF之比与尿液中的该比值相等，且此后不再变化。在13个月内进行的9次实验中，钙（来自尿液标准品）化学沉淀与后续TIMS测量相结合的重现性为1.2%（变异系数）。这与单次实验的重现性一致。从单次血液或尿液测量得出的α估计值比通过反卷积获得的参考值高6 - 10%。这种差异可以用一个校正因子来解释，该因子部分取决于达到钙肠道吸收峰值速率所经过的时间。仪器诱导的质量分馏以及放射性钙的贡献对血液和尿液中示踪剂AFs比值的准确性和重现性有显著影响。
