Interlaboratory comparison of 25-hydroxyvitamin D assays: Vitamin D Standardization Program (VDSP) Intercomparison Study 2 - Part 1 liquid chromatography - tandem mass spectrometry (LC-MS/MS) assays - impact of 3-epi-25-hydroxyvitamin D3 on assay performance.

An interlaboratory comparison study was conducted by the Vitamin D Standardization Program (VDSP) to assess the performance of liquid chromatography - tandem mass spectrometry (LC-MS/MS) assays used for the determination of serum total 25-hydroxyvitamin D (25(OH)D), which is the sum of 25-hydroxyvitamin D2 (25(OH)D2) and 25-hydroxyvitamin D3 (25(OH)D3). A set of 50 single-donor samples was assigned target values for concentrations of 25(OH)D2, 25(OH)D3, 3-epi-25-hydroxyvitamin D3 (3-epi-25(OH)D3), and 24R,25-dihydroxyvitamin D3 (24R,25(OH)2D3) using isotope dilution liquid chromatography - tandem mass spectrometry (ID LC-MS/MS). VDSP Intercomparison Study 2 Part 1 includes results from 14 laboratories using 14 custom LC-MS/MS assays. Assay performance was evaluated using mean % bias compared to the assigned target values and using linear regression analysis of the test assay mean results and the target values. Only 53% of the LC-MS/MS assays met the VDSP criterion of mean % bias ≤ |±5%|. For the LC-MS/MS assays not meeting the ≤ |±5%| criterion, four assays had mean % bias of between 12 and 21%. Based on multivariable regression analysis using the concentrations of the four individual vitamin D metabolites in the 50 single-donor samples, the performance of several LC-MS/MS assays was found to be influenced by the presence of 3-epi-25(OH)D3. The results of this interlaboratory study represent the most comprehensive comparison of LC-MS/MS assay performance for serum total 25(OH)D and document the significant impact of the lack of separation of 3-epi-25(OH)D3 and 25(OH)D3 on assay performance, particularly with regard to mean % bias.

Assessment of serum total 25-hydroxyvitamin D assays for Vitamin D External Quality Assessment Scheme (DEQAS) materials distributed at ambient and frozen conditions.

The Vitamin D External Quality Assessment Scheme (DEQAS) distributes human serum samples four times per year to over 1000 participants worldwide for the determination of total serum 25-hydroxyvitamin D [25(OH)D)]. These samples are stored at -40 °C prior to distribution and the participants are instructed to store the samples frozen at -20 °C or lower after receipt; however, the samples are shipped to participants at ambient conditions (i.e., no temperature control). To address the question of whether shipment at ambient conditions is sufficient for reliable performance of various 25(OH)D assays, the equivalence of DEQAS human serum samples shipped under frozen and ambient conditions was assessed. As part of a Vitamin D Standardization Program (VDSP) commutability study, two sets of the same nine DEQAS samples were shipped to participants at ambient temperature and frozen on dry ice. Twenty-eight laboratories participated in this study and provided 34 sets of results for the measurement of 25(OH)D using 20 ligand binding assays and 14 liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. Equivalence of the assay response for the frozen versus ambient DEQAS samples for each assay was evaluated using multi-level modeling, paired t-tests including a false discovery rate (FDR) approach, and ordinary least squares linear regression analysis of frozen versus ambient results. Using the paired t-test and confirmed by FDR testing, differences in the results for the ambient and frozen samples were found to be statistically significant at p < 0.05 for four assays (DiaSorin, DIAsource, Siemens, and SNIBE prototype). For all 14 LC-MS/MS assays, the differences in the results for the ambient- and frozen-shipped samples were not found to be significant at p < 0.05 indicating that these analytes were stable during shipment at ambient conditions. Even though assay results have been shown to vary considerably among different 25(OH)D assays in other studies, the results of this study also indicate that sample handling/transport conditions may influence 25(OH)D assay response for several assays.

Assessment of serum total 25-hydroxyvitamin D assay commutability of Standard Reference Materials and College of American Pathologists Accuracy-Based Vitamin D (ABVD) Scheme and Vitamin D External Quality Assessment Scheme (DEQAS) materials: Vitamin D Standardization Program (VDSP) Commutability Study 2.

An interlaboratory study was conducted through the Vitamin D Standardization Program (VDSP) to assess commutability of Standard Reference Materials® (SRMs) and proficiency testing/external quality assessment (PT/EQA) samples for determination of serum total 25-hydroxyvitamin D [25(OH)D] using ligand binding assays and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A set of 50 single-donor serum samples were assigned target values for 25-hydroxyvitamin D2 [25(OH)D2] and 25-hydroxyvitamin D3 [25(OH)D3] using reference measurement procedures (RMPs). SRM and PT/EQA samples evaluated included SRM 972a (four levels), SRM 2973, six College of American Pathologists (CAP) Accuracy-Based Vitamin D (ABVD) samples, and nine Vitamin D External Quality Assessment Scheme (DEQAS) samples. Results were received from 28 different laboratories using 20 ligand binding assays and 14 LC-MS/MS methods. Using the test assay results for total serum 25(OH)D (i.e., the sum of 25(OH)D2 and 25(OH)D3) determined for the single-donor samples and the RMP target values, the linear regression and 95% prediction intervals (PIs) were calculated. Using a subset of 42 samples that had concentrations of 25(OH)D2 below 30 nmol/L, one or more of the SRM and PT/EQA samples with high concentrations of 25(OH)D2 were deemed non-commutable using 5 of 11 unique ligand binding assays. SRM 972a (level 4), which has high exogenous concentration of 3-epi-25(OH)D3, was deemed non-commutable for 50% of the LC-MS/MS assays.

Urine Comprehensive Drug Screen, Low Birth Weight and Withdrawal Symptoms in a Neonatal Unit: A Case Control Study.

OBJECTIVE: Maternal drug abuse may influence neonatal outcomes. We compared neonatal outcomes of patients with urine screened positive for commonly abused drugs (CAD) versus those who were screened negative, and reviewed the pattern of drugs detected at a university teaching hospital. METHODS: Urine samples collected from babies with suspected illicit drug exposure who were admitted to the neonatal unit were sent for comprehensive drug screen (CDS) performed by liquid chromatographytime- of-flight mass spectrometry (LC-TOF/MS). The screening library can detect more than 300 drugs and their metabolites. Fluorescence polarization immunoassay (FPIA) was also used to screen for cannabinoids which were not detected by the present LC-TOF/MS method. Symptoms suggestive of drug exposure and history of maternal substance misuse were recorded. RESULTS: Commonly abused drugs (CAD) including methadone, morphine, codeine, methamphetamine, ketamine, midazolam and heroin were present in the urine specimens of 46 (24.2%) of 190 neonates. Eighty-one (42.6%) urine samples screened positive for other drugs, which include antibiotics, lidocaine and pethidine administered during delivery. Drugs were undetectable in 33.2% samples. Urine positive for CAD was independently associated with maternal history of substance misuse (0.0001), birth-weight 2.5 kg (OR 2.9,0.01), neonatal withdrawal symptomatology (OR=8.89, 0.0001); but not with risk of preterm delivery. Logistic regression demonstrated that neonates with maternal history of substance misuse and CAD positivity were 5.99 (p=0.021) and 5.91 (0.0005) times more likely to have withdrawal symptoms. CONCLUSIONS: CADs are isolated in the CDS of nearly one-fourth of neonates. Neonates with maternal history of CAD exposure as evidenced by positive urine CDS are associated with low birth weight, and symptoms of drug withdrawal.

Achievements and Future Directions of the APFCB Mass Spectrometry Harmonisation Project on Serum Testosterone.

As an outcome of the 2010 Asian Pacific Conference for Chromatography and Mass Spectrometry in Hong Kong, a collaborative working group was formed to promote the harmonisation of mass spectrometry methods. The Mass Spectrometry Harmonisation Working Group resides under the combined auspices of the Asia-Pacific Federation for Clinical Biochemistry and Laboratory Medicine (APFCB) and the Australasian Association of Clinical Biochemists (AACB). A decision was made to initially focus attention on serum steroids due to the common interest of members in this area; with the first steroid to assess being testosterone. In principle, full standardisation with traceability should be achievable for all steroids as they are small compounds with defined molecular weight and structure. In order to achieve this we need certified reference materials, reference methods, reference laboratories, reference intervals and external quality assurance programs; each being an important pillar in the process. When all the pillars are present, such as for serum testosterone, it is feasible to fully standardise the liquid chromatography - tandem mass spectrometry (LC-MS/MS) methods. In a collaborative process with interested stakeholders, we commenced on a pathway to provide ongoing assessment and seek opportunities for improvement in the LC-MS/MS methods for serum steroids. Here we discuss the outcomes to date and major challenges related to the accurate measurement of serum steroids with a focus on serum testosterone.

Mouse Leydig tumor cells produce C-19 steroids, including testosterone.

The mouse Leydig tumor cells (MLTC-1) were derived from a transplantable Leydig cell tumor carried in C57BL/6 mice. The original cell line (M5480) produced testosterone and little progesterone. However, it was later shown that there were two subtypes of the cell line, one producing mainly progesterone and termed M5480P and the other which produced androgens and termed M5480A. MLTC-1 cells are reportedly derived from the former. We studied the production of testosterone by MLTC-1 cells using a specific and sensitive testosterone RIA, tandem mass spectrometry (TMS) and examined the expression of mRNA of some key enzymes involved in steroidogenesis. Although the molar yields were 1:20:60 for testosterone, androstenedione and progesterone, respectively, in response to human chorionic gonadotropin (hCG), testosterone measured by our RIA accounted for 94% of the testosterone immunoreactivity. Both MLTC-1 and Balb/c Leydig cells expressed Steroidogenic Acute Response (StAR) protein mRNA in response to hCG. Cytochrome P450 17alpha-hydroxylase/17,20-lyase mRNA was expressed constitutively in MLTC-1 and Balb/c Leydig cells. Whereas the latter expressed 17beta-hydroxydehydrogenase/17-ketoreductase isoform Type 3mRNA in response to hCG, MLTC-1 cells expressed isoform Type 7 constitutively. The absence of isoform Type 3 in MLTC-1 cells thus may account for the low conversion of androstenedione to testosterone in this cell line. However, with a very specific and sensitive RIA even the low production of testosterone becomes meaningful. In conclusion MLTC-1 cells produce testosterone.

Cadmium and lead in Hong Kong school children.

AIM: Cadmium (Cd) and lead (Pb) are toxic elements in our environment. This study is to determine the reference intervals of Cd and Pb in blood and urine from Hong Kong school children and to identify their determinants. METHODS: A total of 2209 secondary school children and 893 preschool children were recruited. Cd and Pb in blood and urine were measured by inductively-coupled plasma mass spectrometry. RESULTS: Blood Cd was affected by age, smoking and residential district, while urine Cd was influenced by age and blood Cd. Blood Cd was positively correlated with smoking as confirmed by urinary cotinine (rho  = 0.183, p  <  0.001, n = 2074). Blood Pb was dependent on gender and residential district, while urinary Pb was dependent on gender and blood Pb. Students from schools of lower academic grading had higher blood Cd and Pb than those from higher academic grading schools (p < 0.001, respectively). Urinary albumin was positively associated with urinary Cd and Pb. CONCLUSIONS: Using a non-occupationally exposed population, the reference ranges are: blood Cd < 21.9  nmol/L for smokers and < 8.8  nmol/L for non-smokers, and blood Pb < 203.8  nmol/L. Reference intervals for urinary Cd and Pb are also reported.

Cold-vapour atomic absorption spectrometry underestimates total mercury in blood and urine compared to inductively-coupled plasma mass spectrometry: an important factor for determining mercury reference intervals.

AIM: In recent years, the application of inductively-coupled plasma mass spectrometry (ICP-MS) has been used increasingly in clinical laboratories for the measurement of various trace elements and heavy metals. However, full evaluation of this technique has not been conducted to ensure the transfer of comparable results from conventional cold-vapour atomic absorption spectrophotometry (CVAAS) for blood and urine total mercury (Hg) analysis. METHODS: A total of 131 blood and 223 urine samples from both patients and normal healthy subjects were collected from a university-based trace element laboratory and a population survey of healthy school adolescents. Correlation study was conducted for total Hg concentration measured by the traditional on-line digestion with flow injection CVAAS and the newly installed ICP-MS. Reference materials were used for method validation and quality control. Standard addition of fixed amounts of inorganic and methyl Hg standards into blood and urine were performed for recovery study. Bias in total Hg measurement was investigated by re-calibrating both instruments using methyl Hg standards. RESULTS: The intra- and inter-assay coefficients of variation in the ICP-MS were <6% in the range of 14-259 nmol/L for Hg in blood and urine samples assayed. The detection limit was 1.1 nmol/L and linearity was up to 186 nmol/L. The results from analyses of a range of whole blood and urine reference materials agreed well with the certified values. The correlation study showed a significant correlation between ICP-MS and CVAAS with: [ICP-MS] = 7.36 + 1.69*[CVAAS] in blood samples (r = 0.84, p < 0.0001) and [ICP-MS] = 1.90 + 1.14*[CVAAS] in urine samples (r = 0.93, p < 0.0001) for total Hg. Recovery study showed that the % recovery of inorganic Hg in blood for ICP-MS and CVAAS ranged from 83 to 95% and 77 to 84%, respectively, while that of inorganic Hg in urine for ICP-MS and CVAAS ranged from 92 to 126% and 43 to 93%, respectively. For methyl Hg, the % recovery in blood for ICP-MS and CVAAS ranged from 72 to 89% and 37 to 75%, respectively, while that in urine for ICP-MS and CVAAS ranged from 65 to 85% and 29 to 42%, respectively. When both instruments were re-calibrated using methyl Hg standards, the blood and urinary total Hg results in ICP-MS were corrected at 24% and -11% of CVAAS, respectively. CONCLUSIONS: Analysis of total Hg was underestimated at about 69% in blood and 14% in urine using the traditional CVAAS method compared to ICP-MS, plausibly due to incomplete oxidation and reduction of methyl Hg species in CVAAS method. The normal limit of blood total Hg concentration has been targeted at <50 nmol/L based on the traditional CVAAS method, and the in vivo proportion of methyl Hg of individuals mainly depends on the dietary intake of seafood. Therefore, for clinical laboratories preparing to change over to ICP-MS method for total Hg analysis, the local reference interval for blood total Hg should be re-determined using a non-occupationally exposed population. Otherwise, over-diagnosis of Hg intoxication can result. We have found that by using ICP-MS for total Hg analysis, the local reference range in blood was <77 nmol/L while in spot urine was <15 nmol/L or 1.2 nmol/mmol of creatinine.