Trace element analysis in hair: factors determining accuracy, precision, and reliability.

Trace element analysis in biological samples has improved significantly over the last 40 years. Improvements in instrumentation such as inductively coupled plasma-mass spectrometry and microwave digestion have resulted in improved precision, accuracy, reliability, and detection limits. The analysis of human scalp hair has benefited significantly from these improvements. A recent article in the Journal of the American Medical Association found significant inter-laboratory variation amongst several laboratories performing trace metal hair testing. It concluded that standardization was necessary to improve inter-laboratory comparability, and an accompanying commentary described the characteristics of a laboratory that should be used in performing hair analysis. The objective of this study is to demonstrate that good laboratory practices will generate precise, accurate, and reliable results. A method for establishing reference ranges and specific data on an analytical method will also be presented. The use of prescribed clinical quality control, including method validation, proficiency testing, split sampling, and good laboratory practices clearly demonstrates that measuring trace elements in hair can be analytically valid.

The risk of diabetes in a subsequent pregnancy associated with prior history of gestational diabetes or macrosomic infant.

Prior studies suggest that diagnosis of gestational diabetes is associated with increased risk for development of gestational diabetes in future pregnancies, and with subsequent onset of established diabetes. The magnitudes of these risks have not been measured. Using linked birth certificate data from Washington State it is possible to identify all women with two or more births occurring during 1984-91. All women with gestational diabetes (n=1375) or with established diabetes (n=220), during their pregnancy for the second or greater birth were identified, and a control group consisting of women whose second or greater birth was not complicated by either condition was randomly selected (n=6380). Data from the birth certificate, for the previous birth, were compared in order to estimate the risks of developing gestational or established diabetes in a subsequent pregnancy among women with prior gestational diabetes relative to women without gestational diabetes. The age-adjusted risk of developing gestational diabetes in the pregnancy for the subsequent birth associated with prior gestational diabetes was 23.2 (95% (confidence interval) CI = 17.2-31.2); the risk of having developed established diabetes by the time of the subsequent birth was 55.5 (95% CI = 34.4-89.4). Women who had a macrosomic infant (>4000 gm) in the prior birth were also at increased risk for developing gestational diabetes (odds ratio OR = 3.3, 95% CI = 2.9-3.8) or established diabetes (OR = 5.8, 95% CI = 4.0-8.5). When data were restricted to patients with only one prior birth, to patients with early prenatal care, to delivery at facilities with long-established protocols for diagnosing gestational diabetes, or to more recent years, the risk estimates remained similarly elevated. The 23-fold increased risk of gestational diabetes associated with having gestational diabetes indicated on the birth certificate of a woman's previous baby, although not unexpected, is still remarkable and reinforces the importance of careful monitoring of women with this history. Although changes in how screening is conducted may account for some of the elevation in risk, our results stayed consistently elevated even when restrictions were made within the data to control for this. The fact that there was a 56-fold increased risk of having developed established diabetes by the time of the subsequent birth on record, associated with prior gestational diabetes, and a 6-fold increased risk associated with a macrosomic infant, supports the idea that these may be early steps in the development of established diabetes, and identifies a group that may benefit from close monitoring and possible intervention.