Clinical Chemistry

Ultrafast selective quantification of methotrexate in human plasma by high-throughput MALDI-isotope dilution mass spectrometry (Article)

Meesters, R.J.W. — 2011-06-01T00:00:00Z

Background: A new analytical MS method using isotope dilution combined with MALDI-triple quadrupole MS/MS has been developed and validated for the determination of methotrexate and 7-hydroxymethotrexate in plasma. Methotrexate, methotrexate-d3, 7-hydroxymethotrexate and 7-hydroxymethotrexate-d3 were monitored by selected reaction monitoring using the transitions m/z 455.2→308.2, 458.2→311.2, 471.2→324.2 and 474.2→327.2 for methotrexate, methotrexate-d3, 7-hydroxymethotrexate and 7-hydroxymethotrexate- d3, respectively. Results: The LLOQ was 1 nmol/l for methotrexate and 7-hydroxymethotrexate while the limit of detection was 0.3 nmol/l for both analytes. The new developed method was cross-validated by a fluorescence polarization immunoassay and tested for its clinical feasibility by measuring plasma samples from patients suffering from acute lymphoblastic leukemia. Plasma methotrexate concentrations ranged between 66.0 and 954 nmol/l and observed 7-hydroxymethotrexate/methotrexate ratios ranged between 0.1 and 32.4, respectively. Conclusion: The new method showed comparable analytical performances as the fluorescence polarization immunoassay, but analyte specificity and sensitivity of the newly developed method were significantly better.

Dried blood spot UHPLC-MS/MS analysis of oseltamivir and oseltamivircarboxylate-a validated assay for the clinic (Article)

Hooff, G.P. — 2011-05-03T00:00:00Z

The neuraminidase inhibitor oseltamivir (Tamiflu®) is currently the first-line therapy for patients with influenza virus infection. Common analysis of the prodrug and its active metabolite oseltamivircarboxylate is determined via extraction from plasma. Compared with these assays, dried blood spot (DBS) analysis provides several advantages, including a minimum sample volume required for the measurement of drugs in whole blood. Samples can easily be obtained via a simple, non-invasive finger or heel prick. Mainly, these characteristics make DBS an ideal tool for pediatrics and to measure multiple time points such as those needed in therapeutic drug monitoring or pharmacokinetic studies. Additionally, DBS sample preparation, stability, and storage are usually most convenient. In the present work, we developed and fully validated a DBS assay for the simultaneous determination of oseltamivir and oseltamivircarboxylate concentrations in human whole blood. We demonstrate the simplicity of DBS sample preparation, and a fast, accurate and reproducible analysis using ultra high-performance liquid chromatography coupled to a triple quadrupole mass spectrometer. A thorough validation on the basis of the most recent FDA guidelines for bioanalytical method validation showed that the method is selective, precise, and accurate (≤15% RSD), and sensitive over the relevant clinical range of 5-1,500 ng/mL for oseltamivir and 20-1,500 ng/mL for the oseltamivircarboxylate metabolite. As a proof of concept, oseltamivir and oseltamivircarboxylate levels were determined in DBS obtained from healthy volunteers who received a single oral dose of Tamiflu®.

Addition of serum-containing medium to cerebrospinal fluid prevents cellular loss over time (Article)

Graaf, M.T. de — 2011-03-12T00:00:00Z

Immediately after sampling, leukocyte counts in native cerebrospinal fluid (CSF) start to decrease rapidly. As the time lapse between CSF collection to analysis is not routinely registered, the clinical significance of decreasing cell counts in native CSF is not known. Earlier data suggest that addition of serum-containing medium to CSF directly after sampling prevents this rapid decrease in leukocyte counts and, thus, may improve the accuracy of CSF cell counting and cell characterization. Here, we prospectively examined the effect of storage time after lumbar puncture on counts of leukocytes and their major subsets in both native CSF and after immediate addition of serum-containing medium, measured by flow cytometry and microscopy. We collected CSF samples of 69 patients in tubes with and tubes without serum-containing medium and determined counts of leukocytes and subsets at 30 minutes, 1 hour, and 5 hours after sampling. Compared to cell counts at 30 minutes, no significant decrease in cell number was observed in CSF with serum-containing medium 1 and 5 hours after sampling, except for the granulocytes at 1 hour. In native CSF, approximately 50% of leukocytes and all their subsets were lost after 1 hour, both in flow cytometric and microscopic counting. In 6/7 (86%) samples with mild pleocytosis (5-15 × 10(6) leukocytes/l), native CSF at 1 hour was incorrectly diagnosed as normocellular. In conclusion, addition of serum-containing medium to CSF directly after sampling prevents cell loss and allows longer preservation of CSF cells prior to analysis, both for microscopic and flow cytometric enumeration. We suggest that this protocol results in more accurate CSF cell counts and may prevent incorrect conclusions based on underestimated CSF cell counts.

External quality assurance of circulating tumor cell enumeration using the CellSearch® system: A feasibility study (Article)

Kraan, J. — 2011-03-01T00:00:00Z

Background: Circulating tumor cells (CTCs) are cells that have detached from solid tumors and entered the blood. CTCs can be detected, among others, by semi-automated immunomagnetic enrichment and image cytometry using CellSearch® (Veridex, Raritan, NJ). We studied the feasibility of external quality assurance (EQA) of the entire CellSearch procedure from blood draw to interpretation of results in multiple laboratories. Methods: Blood samples from six cancer patients and controls were distributed to 14 independent laboratories to test between-laboratory, between-assay, and between-instrument variation. Additionally, between-operator variability was assessed through the interpretation of blinded images of all blood samples on a website. Results: Shipment and storage of samples had no influence on CTC values. Between-instrument (coefficient of variation (CV) < 12%) and between-assay variation was low (CV ≤ 20%), indicating high reproducibility. However, between-laboratory CV ranged from 45 to 64%. Although inter-operator agreement on image interpretation (Fleiss' I° statistics) ranged from " to "almost perfect," image interpretation, particularly of samples containing high numbers of apoptotic cells, was the main contributor to between-laboratory variation. Conclusions: This multicenter study shows the feasibility of an EQA program for CTC detection in patient samples, and the importance of continuation of such a program for the harmonization of CTC enumeration.

Nonlinear relationship between mycophenolate mofetil dose and mycophenolic acid exposure: Implications for therapeutic drug monitoring (Article)

Winter, B.C.M. de — 2011-03-01T00:00:00Z

Background and objectives: Mycophenolate mofetil (MMF) is an immunosuppressive drug used in renal transplant patients. Upon oral administration it is hydrolyzed to the active agent mycophenolic acid (MPA). In renal transplant recipients, MMF therapy is optimal when the area under the curve of MPA is 30 to 60 mg·h/L. When MMF doses are adjusted, a linear relationship between dose and MPA exposure is assumed. In this study, the linearity of MMF pharmacokinetics was investigated. Design, setting, participants, & measurements: MPA concentration-time profiles from renal transplant recipients cotreated with cyclosporine (n = 140) or tacrolimus (n = 101) were analyzed retrospectively using nonlinear mixed-effects modeling. The correlation between the MMF dose and the pharmacokinetics parameters was evaluated. Results: In the developed population pharmacokinetics model MPA clearance and the central volume of distribution were correlated with cyclosporine coadministration and time posttransplantation. The pharmacokinetics of MPA were not linear. Bioavailability decreased with increasing MMF doses. Compared with an MMF dose of 1000 mg (=100%), relative bioavailability was 123%, 111%, 94%, and 90% in patients receiving MMF doses of 250, 500, 1500, and 2000 mg in combination with cyclosporine (P < 0.001); respective values in tacrolimus-cotreated patients were 176%, 133%, 85%, and 76% (P < 0.001). Because of the decreasing relative bioavailability, MPA exposure will increase less than proportionally with increasing MMF doses. Conclusions: MMF exhibits nonlinear pharmacokinetics. This should be taken into account when performing therapeutic drug monitoring. Copyright

Impact of reduced chemotherapy treatment for good risk childhood acute lymphoblastic leukaemia on infectious morbidity (Article)

Tilburg, C.M. van — 2011-02-01T00:00:00Z

Reducing infectious morbidity is an important goal to improve childhood acute lymphoblastic leukaemia (ALL) survival. To explore the impact of chemotherapy reduction on infectious morbidity, we compared outpatient and inpatient infectious morbidity of reduced versus intensive (conventional) chemotherapy. One hundred and seventy-one children newly diagnosed with ALL between 2004 and 2007 and treated according to the Dutch Childhood Oncology Group ALL 10 protocol were prospectively followed during the 2-year treatment course. Stratified by minimal residual disease, 54 patients received reduced (standard risk; SR) and 117 patients received intensive (medium risk; MR) intensification/maintenance treatment. SR outpatients had a median of 1 febrile episode versus 4 in MR outpatients (P=0·002). SR patients had fewer hospitalizations for fever. They were admitted a median of 0 times, with a median of 0days of hospitalization, median 0days of fever, median 0 times chemotherapy interruption and median 0 times intravenous antibiotics. MR patients were admitted for fever median 2 times (P<0·001) with 10days of hospitalization (P<0·001), 2days of fever (P<0·001), one chemotherapy interruption (P<0·001) and two intravenous antibiotics administration (P<0·001). These data indicate that reduced intensification/maintenance compared to conventional intensive intensification/maintenance chemotherapy for good risk childhood ALL resulted in major decrease of infectious morbidity.

Preconception folic acid use modulates estradiol and follicular responses to ovarian stimulation (Article)

Twigt, J.M. — 2011-02-01T00:00:00Z

Background: Folate is a methyl donor. Availability of folate affects DNA methylation profiles and thereby gene expression profiles. We investigated the effects of low-dose folic acid use (0.4 mg/d) on the ovarian response to mild and conventional ovarian stimulation in women. Methods: In a randomized trial among subfertile women, 24 and 26 subjects received conventional and mild ovarian stimulation, respectively. Blood samples were taken during the early follicular phase of the cycle prior to treatment and on the day of human chorionic gonadotropin administration for determination of serum total homocysteine, anti-Müllerian hormone (AMH), estradiol, and folate. Folic acid use was validated by questionnaire and serum folate levels. Preovulatory follicles were visualized, counted, and diameters recorded using transvaginal ultrasound. The relation between folic acid use and ovarian response was assessed using linear regression analysis. Results: Folic acid use modified the ovarian response to ovarian stimulation treatment. The estradiol response was higher in nonfolic acid users receiving conventional treatment [βinteraction=0.52 (0.07- 0.97); P = 0.03], and this effect was independent of serum AMH levels and the preovulatory follicle count. In the conventional treatment, themeanfolliclenumberwasalso greater in nonusers compared with the users group (14.1 vs. 8.9, P = 0.03). Conclusion: Low-dose folic acid use attenuates follicular and endocrine responses to conventional stimulation, independent of AMH and follicle count. The nature of this observation suggests that the effect of folic acid is most prominent during early follicle development, affecting immature follicles. Deleterious effects of folate deficiency, like DNA hypomethylation and oxidative stress, can help to explain our observations.

Congenital heart defects and biomarkers of methylation in children: A case-control study (Article)

Obermann-Borst, S.A. — 2011-02-01T00:00:00Z

Eur J Clin Invest 2011; 41 (2): 143-150Background Derangements in the maternal methylation pathway, expressed by global hypomethylation and hyperhomocysteinemia, are associated with the risk of having a child with a congenital heart defect (CHD). It is not known whether periconception exposure to these metabolic derangements contributes to chromosome segregation and metabolic programming of this pathway in the foetus.Design In a Dutch population-based case-control study of 143 children with CHD and 186 healthy children, we investigated S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), total homocysteine (tHcy), the vitamins folate and B12 and the functional single nucleotide polymorphisms in the folate gene MTHFR 677C>T and 1298A>C. Comparisons were made between cases and controls adjusting for age, medication, vitamin use and CHD family history.Results In the overall CHD group, the median concentrations of SAM (P = 0.011), folate in serum (P = 0.021) and RBC (P = 0.030) were significantly higher than in the controls. Subgroup analysis showed that this was mainly attributable to complex CHD with higher SAM (P < 0.001), SAH (P = 0.012) and serum folate (P = 0.010) independent of carriership of MTHFR polymorphisms. Highest concentrations of SAM, SAH and folate RBC were observed in complex syndromic CHD. The subgroup of children with Down syndrome, however, showed significantly higher SAH (P = 0.037) and significantly lower SAM:SAH ratio (P = 0.034) compared with other complex CHD, suggesting a state of global hypomethylation.Conclusion High concentrations of methylation biomarkers in very young children are associated with complex CHD. Down syndrome and CHD may be associated with a global hypomethylation status, which has to be confirmed in tissues and global DNA methylation in future studies.

A derangement of the maternal lipid profile is associated with an elevated risk of congenital heart disease in the offspring (Article)

Smedts, H.P.M. — 2010-12-27T00:00:00Z

Background and aims: Maternal hyperglycaemia and hyperhomocysteinaemia are risk factors for congenital heart disease (CHD). These metabolic derangements and deranged lipid levels are associated with adult cardiovascular disease. We examined whether maternal lipid levels are associated with the risk of CHD offspring. Methods and Results: From 2003 onwards, a case-control study was conducted. Participants were mothers of children with (n = 261) and without (n = 325) CHD. At around 16 months after the index-pregnancy, maternal lipid levels were determined. Maternal characteristics and lipid levels were compared by Student's t-test. In a multivariable logistic regression model, risk estimates were calculated for associations between CHD and lipid levels. Adjustments were made for maternal age, diabetes, ethnicity, body mass index (BMI), parity, periconception folic acid use and total homocysteine levels. Outcome measures are presented in (geometric) means (p5-p95) and odds ratios (ORs) with 95% confidence intervals (CIs). Case mothers showed higher cholesterol (4.9 vs. 4.7 mmol l-1, P < 0.05), low-density lipoprotein (LDL)-cholesterol (3.2 vs. 3.0 mmol l-1, P < 0.05), apolipoprotein B (84.0 vs. 80.0 mg dl-1, P < 0.01) and homocysteine (10.8 vs. 10.2 μmol l-1, P < 0.05) than controls. LDL-cholesterol above 3.3 mmol l-1(OR 1.6 (95%CI, 1.1-2.3)) and apolipoprotein B above 85.0 mg dl-1were associated with an almost twofold increased CHD risk (OR 1.8 (95%CI, 1.2-2.6)). This was supported by elevated CHD risks per unit standard deviation increase in cholesterol (OR 1.2 (95% CI 1.03-1.5)), LDL-cholesterol (OR 1.3 (95%CI, 1.1-1.6) and apolipoprotein B (OR 1.3 (95% CI 1.1-1.6)). Apolipoprotein B was most strongly associated with CHD risk. Conclusion: A mildly deranged maternal lipid profile is associated with an increased risk of CHD offspring.

Polymorphisms in the multidrug resistance gene MDR1 (ABCB1) predict for molecular resistance in patients with newly diagnosed chronic myeloid leukemia receiving high-dose imatinib (Article)

Deenik, W. — 2010-12-23T00:00:00Z

The preconception nutritional status of women undergoing fertility treatment: Use of a one-year post-delivery assessment (Article)

Driel, L.M.J.W. van — 2010-12-01T00:00:00Z

Background&Aims: A poor maternal nutritional status in the preconception period is associated with adverse pregnancy outcomes. A valid standardized assessment period after pregnancy reflecting the preconception nutritional status is missing. Therefore, this study aimed to validate the assessment period at around 1 year after delivery in women undergoing fertility treatment. Methods: In a prospective study including 30 women with a fertility problem, we compared nutrient intakes from a food frequency questionnaire and biomarkers related to the homocysteine pathway in blood, at two assessment periods, i.e., preconceptionally and 1 year after delivery. We used a linear mixed model and adjusted for possible confounders, such as body mass index and folic acid supplement use. Results: The energy-adjusted nutrient intakes were not significantly different between the two assessment periods, except for higher retinol, alcohol and vitamin B2 and lower carbohydrate intakes at around 1 year after delivery. The intraclass correlation coefficients of the nutrients ranged from 0.3 to 0.7. After adjustment, none of the biomarkers was significantly different between the two assessment periods. The intraclass correlation coefficients of the biomarkers were all ≥0.5. Conclusions: An assessment at around 1 year after delivery seems to adequately reflect the preconception nutritional status of women with a fertility problem, however larger confirmatory studies are required.

The preconception nutritional status of women undergoing fertility treatment: Use of a one-year post-delivery assessment (Article)

Driel, L.M.J.W. van — 2010-12-01T00:00:00Z

A new ultrafast and high-throughput mass spectrometric approach for the therapeutic drug monitoring of the multi-targeted anti-folate pemetrexed in plasma from lung cancer patients (Article)

Meesters, R.J.W. — 2010-12-01T00:00:00Z

An analytical assay has been developed and validated for ultrafast and high-throughput mass spectrometric determination of pemetrexed concentrations in plasma using matrix assisted laser desorption/ionization-triple quadrupole-tandem mass spectrometry. Patient plasma samples spiked with the internal standard methotrexate were measured by multiple reaction monitoring. The detection limit was 0.4 fmol/μL, lower limit of quantification was 0.9 fmol/μL, and upper limit of quantification was 60 fmol/μL, respectively. Overall observed pemetrexed concentrations in patient samples ranged between 8.7 (1.4) and 142.7 (20.3)∈pmol/μL (SD). The newly developed mass spectrometric assay is applicable for (routine) therapeutic drug monitoring of pemetrexed concentrations in plasma from non-small cell lung cancer patients.

The spleen as a site for hematopoiesis (Article)

Dor, F.J.M.F. — 2010-11-15T00:00:00Z

On the use of prostate-specific antigen for screening of prostate cancer in European Randomised Study for Screening of Prostate Cancer (Article)

Bangma, C.H. — 2010-11-01T00:00:00Z

Prostate-specific antigen (PSA) has been the main drive for early detection of prostate cancer (PCa), including in population-based screening as in the European Randomised Study for Screening of Prostate Cancer (ERSPC). The specificity of PSA to indicate men with biopsy detectable prostate cancer can be improved by adding information obtained by new biomarkers, such as PSA isoforms. This improvement is needed to increase the efficacy of the screening procedure for the population-based as well as the individual screening. Various PSA isoforms, kallikreins and molecular markers have been validated in various cohorts from ERSPC of men with and without PCa in order to design the optimal diagnostic procedure for screening asymptomatic men. So far, most promising results have been obtained from the analysis of free PSA, proPSA, nicked PSA and hK2. The use of free PSA in addition to total PSA reduces the number of negative sextant biopsies at a PSA cut-off level of 3 ng/ml at initial screening with 30%, at the cost of losing 10% of detectable cancers that are predominantly well differentiated on histology. Further addition of PSA isoforms and hK2 only improve ROC curves in selected samples by a maximum of 5%. Molecular markers like PCA3 and TMPRSS2 in urine do not appear to be useful but they have been assessed insufficiently so far. The level of PSA at initial screening is highly predictive for the chance of being diagnosed with PCa later on in life. The changes in PSA over time after initial screening (like PSA-velocity and PSA-doubling time) are statistically different between men with detectable cancers versus those without (PSA-doubling time 5.1 versus 6.1 years), but this does not contribute significantly to population-based screening overall. Changes in specificity need to be related to a cost efficacy evaluation in the final analysis of ERSPC.

Levels of circulating endothelial cells in normotensive and severe preeclamptic pregnancies (Article)

Strijbos, M.H. — 2010-11-01T00:00:00Z

Background: Preeclampsia is a disease hypothesized to originate from widespread endothelial dysfunction or damage. This study investigated whether circulating endothelial cells (CEC) can serve as a surrogate marker for disease severity in patients with preeclampsia, and if their number correlates to serum endothelial biomarkers for activation, dysfunction, or damage of those cells. Methods: Blood was drawn consecutively from 30 patients admitted with a diagnosis of severe preeclampsia. Thirty healthy, normotensive, patients matched for age, body mass index, and gestational age served as a control group. We determined the number of CEC and serum concentrations of biomarkers indicative of endothelial damage (thrombomodulin) and activation (E-selectin), and the antiangiogenic protein (endoglin), which reflects endothelial dysfunction. Results: Median CEC counts did not differ significantly between preeclamptic patients and the control group (median 5.3 vs. 3.5 CEC/mL, respectively) and were mostly within the normal range (i.e., <20 CEC/mL). However, serum concentrations of thrombomodulin (median 3.6 vs. 5.2 ng/mL; P = 0.006), E-selectin (median 32.0 vs. 42.9 ng/mL; P = 0.02), and especially endoglin (median 5.0 vs. 76.2 ng/mL; P < 0.0001) were significantly increased in severe preeclamptic patients. CEC counts did not correlate with any of the clinical parameters or routinely determined laboratory indices. Conclusion: Preeclampsia is characterized by endothelial dysfunction and activation rather than actual endothelial damage as characterized by increased CEC counts.

Levels of circulating endothelial cells in normotensive and severe preeclamptic pregnancies (Article)

Strijbos, M.H. — 2010-11-01T00:00:00Z

Potential value of serum total IgE for differentiation between autoimmune pancreatitis and pancreatic cancer (Article)

Toorenenbergen, A.W. van — 2010-11-01T00:00:00Z

Abstract: Autoimmune pancreatitis (AIP) is associated with a marked elevation of serum total IgG4. Although there is evidence of autoimmunity in AIP, there are also signs of an allergic nature of its pathogenesis. Therefore, we determined both IgE and IgG4 in 13 patients with AIP, in 12 patients with pancreatic carcinoma and in 14 patients with atopic allergy and investigated the relationship between IgE and IgG4. Total IgG4 was determined by automated nephelometry and total IgE by automated enzyme fluoroimmunoassay. Both total IgE and total IgG4 levels in patients with AIP were significantly higher than those in patients with pancreatic carcinoma (P = 0.0004 and P = 0.015, respectively). There was a significant correlation between the total IgE and total IgG4 levels in patients with AIP and patients with atopic allergy (rs = 0.82,P = 0.0006 and rs = 0.88,P < 0.0001, respectively). The IgE/ IgG4 ratio in sera from patients with atopic allergy was significantly different (P = 0.0012) from this ratio in sera from patients with AIP. These results suggest that analysis of total IgE in serum might be useful in the differentiation between autoimmune pancreatitis and pancreatic carcinoma.

Amino-terminal pro-brain natriuretic peptide (NT-proBNP) is a biomarker of cardiac filling pressures in pre-eclampsia (Article)

Speksnijder, L. — 2010-11-01T00:00:00Z

Objective: To evaluate if amino-terminal pro-brain natriuretic peptide (NT-proBNP) plasma levels reflect intracardiac filling pressures in pre-eclamptic patients. Study design: In a cross-sectional study we investigated 22 untreated critically ill pre-eclamptic women between 22 and 34 weeks gestation. All patients underwent intra-arterial blood pressure and central hemodynamic measurements and NT-proBNP was determined in stored plasma. Baseline characteristics, plasma NT-proBNP concentrations and relevant laboratory variables were investigated for correlations with hemodynamic values using Spearman's rank correlation test. Results: No significant correlations were demonstrated between NT-proBNP concentrations and variables associated with the severity of the pre-eclampsia. We found significant positive correlations between NT-proBNP and diastolic pulmonary pressure (r = 0.59; p = 0.005) and pulmonary capillary wedge pressure (PCWP) (r = 0.51; p = 0.015). Multiple linear regression analysis showed that the association between NT-proBNP and PCWP was not affected by creatinine level. Conclusion: NT-proBNP is a biomarker of left ventricular cardiac filling pressures in untreated pre-eclamptic patients.

Retinol status of newborn infants is associated with congenital diaphragmatic hernia (Article)

Beurskens, L.W.J.E. — 2010-10-01T00:00:00Z

OBJECTIVE: Genetic analyses in humans suggest a role for retinoid-related genes in the pathogenesis of congenital diaphragmatic hernia (CDH). The goal of this study was to investigate the vitamin A status of mothers and their newborns in association with CDH. METHODS: We conducted a hospital-based, case-control study with 22 case and 34 control mothers and their newborns. In maternal and cord blood samples, retinol and retinol-binding protein (RBP) levels were measured with high-performance liquid chromatography and an enzyme-linked immunosorbent assay, respectively. Univariate and multivariate logistic regression analyses were performed to determine crude and adjusted risk estimates. RESULTS: Case newborns had significantly lower levels of retinol (0.60 vs 0.76 μmol/L; P=.003) and RBP (5.42 vs 7.11 mg/L; P=.02) than did control newborns. The multivariate logistic regression analysis showed lower levels of retinol and RBP in association with CDH risk; the odds ratio for retinol levels of <15th percentile (<0.61 μmol/L) was 11.11 (95% confidence interval: 2.54-48.66; P=.001), and that for RBP levels of <15th percentile (<4.54 mg/L) was 4.00 (95% confidence interval: 1.00 -15.99; P=.05). Retinol and RBP levels were not different between case and control mothers. CONCLUSIONS: CDH is strongly associated with low retinol and RBP levels in newborns, independent of maternal retinol status. This is an important finding supporting the idea that human CDH is linked with abnormal retinoid homeostasis.