Prevalence of pseudonatremia in a clinical laboratory - role of the water content.

BACKGROUND: Sodium concentration is a frequently used marker to discriminate between differential diagnoses or for clinical follow-up. Pseudonatremia, as a result of indirect ion-selective electrode (ISE) measurements in automated chemistry analyzers, can lead to incorrect diagnosis and treatment. We investigated whether the estimated water content, based on total protein and lipid concentrations, can be used to reduce diagnoses of pseudonatremia. METHODS: Indirect and direct ISE measurements of sodium were compared in blood samples from intensive care unit (ICU) (n = 98) and random non-ICU patients (n = 100). Differences between direct measurements using whole blood and lithium-heparin plasma were also determined. Water content, estimated by a linear combination of total protein and lipid concentrations, was used to correct indirectly measured sodium concentrations. The prevalence of pseudonatremia was evaluated in the ICU patient group. RESULTS: An absolute difference of 3 mmol/L was observed between direct measurements using lithium-heparin plasma and whole blood, with higher concentrations in plasma. Additionally, we observed that differences between indirect and direct measurements displayed a linear relationship with the estimated water content. The prevalence of pseudohypernatremia after indirect measurements (32%) was reduced when measurements were corrected for water content (19%). CONCLUSIONS: In critically ill patients, sodium concentrations should be preferably measured by direct measurements. Whole blood is the preferred material for these measurements. For routine sodium analyses in other patients, correction using the estimated water content appears promising in reducing the prevalence of pseudohypernatremia by indirect measurements.

The effect of paraproteins on the erythrocyte sedimentation rate: a comparison between the StarrSed and TEST 1.

BACKGROUND: The principle of the erythrocyte sedimentation rate (ESR) as assessed by TEST 1 is different from that of Westergren-based methods. This could result in different influences on the tests by paraproteins. METHODS: We investigated the effect of paraproteins on ESR readings by TEST 1 (y) and the StarrSed (x), a Westergren-based method, in 142 patients with paraproteinaemia. Agreement (Passing-Bablok) and bias (Bland-Altman) between methods was investigated and compared with that of a control population. RESULTS: A poor agreement between the two methods was found in patients with a paraprotein (y = 0.67x + 3.3) in comparison with that of the control population (y = 0.96x + 0.2). Large differences between methods were present when ESR readings were >40 mm/hour, but clinical interpretation was similar in 90% of cases. Linear regression showed a concentration dependent influence of paraproteins on ESR readings by the StarrSed, especially for immunoglobulin class IgM. CONCLUSION: ESR readings by TEST 1 result in similar clinical interpretation for most subjects, but readings are less influenced by the presence of a paraprotein than those of a Westergren-based method.

The transient increase of oxidative stress during normal pregnancy is higher and persists after delivery in women with pre-eclampsia.

OBJECTIVES: Glutathione, an intracellular tripeptide, functions in the protection of cells against free radicals and toxins of endogenous and exogenous origin. To maintain the intracellular redox status in presence of reactive oxygen species, glutathione (GSH) and other thiols are oxidized. The oxidative status of thiols is reflected by the free-to-oxidized ratio and is a real-time measure for oxidative stress. Previously, we have reported abnormal ratios for the thiols cysteine (Cys), homocysteine (Hcy) and cysteinylglycine (CysGly) in women with pre-eclampsia. The aims of this study were to confirm our previous findings in a different case-control cohort and more importantly to determine whether these differences persist postpartum. STUDY DESIGN: At onset of disease and at 6-8 weeks postpartum we analyzed whole blood of 41 women with pre-eclampsia and of 31 women with normotensive pregnancies for the free-to-oxidized ratio of thiols by the assessment of free and oxidized thiol levels using high performance liquid chromatography. Differences between values were determined using either the paired t-test (antepartum versus postpartum) or the t-test (pre-eclampsia versus normotensive pregnancy). RESULTS: Antepartum levels of free GSH as well as the free-to-oxidized ratios of Hcy were lower in pre-eclampsia and normotensive pregnancy when compared with corresponding postpartum values (P<0.0001 and P<0.01, respectively). Moreover, the free-to-oxidized ratio for Hcy was significantly lowered in pre-eclamptic compared with normotensive women, during as well as after pregnancy (both P< or =0.01). CONCLUSION: The data suggest that pregnancy is a state of higher oxidative stress when compared to the postpartum period. In women with pre-eclampsia, oxidative stress is higher and persists in the postpartum period.

Maternal antioxidant concentrations after uncomplicated pregnancies.

BACKGROUND: To analyse the post-partum concentrations of intra- and extra-cellular blood antioxidants in women with uncomplicated pregnancies. METHODS: Whole blood and plasma thiols, plasma vitamin E and C, serum cholesterol and triglyceride, ferric reducing ability of plasma (FRAP) concentrations were compared between women delivered by caesarean section (n=17) or spontaneous delivery (n=10). A repeated mixed model was used for statistical analysis. RESULTS: The majority of whole blood thiols increased significantly in both groups the first days post-partum. However, within the caesarean group free cysteine, oxidised cysteine, homocysteine and glutathione and plasma cysteine and homocysteine levels dropped significantly after 24 h, while FRAP levels peaked significantly in this group. Plasma vitamin E levels decreased significantly in both groups within 24 to 48 h after delivery. Independent of the way of delivery whole blood and plasma thiols were significantly increased and vitamin E levels were significantly decreased 3 months post-partum while plasma vitamin C levels and FRAP were unchanged compared to ante-partum levels. DISCUSSION: Decreased plasma vitamin E levels shortly post-partum are associated with decreased lipid peroxidation. The 24 h post-partum drop of some plasma and whole blood thiols in the caesarean group may be due to prolonged fasting.

Distribution of components of the glutathione detoxification system across the human placenta after uncomplicated vaginal deliveries.

The function of the glutathione-related detoxification system plays an important role to ensure an uncomplicated pregnancy outcome. This study was performed to investigate whether the components of the glutathione-related detoxification system are equally distributed among the different cotelydons in the human placenta. We measured glutathione, cysteine, glutathione S-transferase (GST) isoenzyme levels (GSTA1+A2, GSTP1, GSTM1 and GSTT1), enzyme activities of glutathione S-transferase and glutathione peroxidases, protein carbonyl levels, and antioxidant capacities at twelve different standardized positions in six placentae from healthy women after uncomplicated pregnancy and vaginal delivery. Data were statistically evaluated with a Friedman two-way ANOVA with Bonferroni correction. 'Foetal'-side values were not significantly different from those at the 'maternal'-side. Except for GSTA1+A2, no significant differences were found between different sampling sites indicating that the distribution of all parameters measured was homogenous throughout the placenta. Since levels of GSTA1+A2 were minor compared to those of GSTP1 and GSTT1, the clinical relevance of this heterogeneity may be limited. These results implicate that the location of sampling is not important as long as biopsies are taken from physiological cotelydons.

Glutathione and glutathione S-transferases A1-1 and P1-1 in seminal plasma may play a role in protecting against oxidative damage to spermatozoa.

OBJECTIVE: To study the levels of glutathione, glutathione S-transferase A1-1, and glutathione S-transferase P1-1 in seminal fluid of fertile and subfertile men. DESIGN: Retrospective case-control study. SETTING: Departments of gastroenterology, obstetrics and gynecology, and epidemiology and biostatistics in a university medical center. PATIENT(S): Twenty-five subfertile men visiting the fertility clinic and 25 fertile men from midwife practices were recruited. INTERVENTION(S): Collection of semen of subfertile and fertile men. MAIN OUTCOME MEASURE(S): Plasma levels of glutathione and glutathione S-transferases A1-1 and P1-1 in relation to seminal characteristics. RESULT(S): Glutathione, glutathione S-transferase A1-1, as well as glutathione S-transferase P1-1 were found in considerable amounts in seminal fluid of subfertile and fertile men. No differences between groups were found for glutathione S-transferases A1-1 and P1-1. Also, no associations with sperm count, motility, or morphology could be detected. Fertile men had significantly higher glutathione levels as compared with the case of subfertile men. Associations of glutathione with sperm motility quality (r(s) = 0.321) and abnormal sperm morphology (r(s) = -0.496) were found. CONCLUSION(S): The presence of glutathione S-transferases A1-1 and P1-1 in seminal fluid suggests a role in the protection against (oxidative) damage of spermatozoa, whereas glutathione may play a role in male fertility.

Collection of blood specimens by venipuncture for plasma-based coagulation assays: necessity of a discard tube.

The Clinical and Laboratory Standards Institute (CLSI) recently abandoned its recommendation for drawing a discard tube when performing a prothrombin time (PT)/international normalized ratio (INR) or an activated partial thromboplastin time (APTT). Because there is currently no evidence that a discard tube is necessary for more specialized coagulation assays, we studied the need for a discard tube for some of these tests. Blood was obtained from 88 subjects in 2 subsequent citrate tubes. Platelet-free plasma was tested for PT, APTT, antithrombin, protein C, and factors II, V, VIII, IX, and X. Difference and bias between tubes were tested using the Wilcoxon signed rank test and Bland-Altman plots. For only APTT, antithrombin, and protein C was a small, statistically significant mean bias found (0.5 seconds; P = .001; -0.7%, P = .002; and -0.8%, P < .0001, respectively), but the bias of individual samples was not clinically relevant. This was also true for the other parameters tested. The recent CLSI recommendation that a discard tube is not necessary for PT/INR and APTT can be extended to include more specialized plasma-based coagulation assays as identified in this study.

A longitudinal study of antioxidant status during uncomplicated and hypertensive pregnancies.

BACKGROUND: To study the possible involvement of an (im)balance between oxidants and antioxidants in pre-eclampsia concentrations of intra- and extracellular blood antioxidants in women with uncomplicated and hypertensive pregnancies, they were studied preconceptionally and throughout pregnancy. METHODS: In uncomplicated pregnancies (n = 19) and hypertensive pregnancies (n = 6) concentrations of whole blood and plasma thiols, plasma vitamins/E and C, hemoglobin, and hematocrit were assessed at preconception, 6, 10, 20, and 37 weeks of gestational age, as well as six weeks postpartum. A repeated mixed model was used for statistical analysis. RESULTS: Vitamin C and most whole blood and plasma thiol concentrations decreased during pregnancy, while vitamin E, whole blood oxidized cysteinyl-glycine and the ratio of free to oxidized homocysteine revealed a linear increase during pregnancy. Postpartum plasma cysteine and vitamin C levels and the ratio of free to oxidized levels of cysteine, cysteinyl-glycine, and glutathione were significantly (p <0.05) lower as compared to preconceptional levels, whereas whole blood oxidized cysteine, cysteinyl-glycine and glutathione levels, and whole blood and plasma homocysteine levels were significantly (p <0.05) higher six weeks after delivery. Plasma cysteine and homocysteine, and whole blood oxidized cysteine and homocysteine levels were significantly (p <0.05) higher at 37 weeks of gestational age in the hypertensive group compared to those in the uncomplicated group. There were no other differences between the hypertensive and uncomplicated groups. CONCLUSION: In normal pregnancy there seems a balance between antioxidant and oxidant concentrations despite modest oxidative stress. In mildly hypertensive pregnancies a marginal imbalance may occur.

N-acetyl-transferase phenotype and risk for preeclampsia.

OBJECTIVE: This study was undertaken to determine whether the N-acetyltransferase (NAT) phenotype contributes to the susceptibility for the development of preeclampsia. STUDY DESIGN: The NAT acetylator status was determined by measuring urinary caffeine metabolites in 134 nonpregnant women with a history of preeclampsia and in 109 control women with uncomplicated pregnancy. The chi(2) and logistic regression analyses were used for statistical evaluation of differences in acetylator status. RESULTS: Significantly more fast acetylators were found among the women with a history of preeclampsia (46.3%) than among the controls (25.4%). Fast acetylators showed an odds ratio of 2.5 (95% CI 1.4-4.3) for preeclampsia. No differences in the acetylator status were found between women with a history of preeclampsia only and those with the HELLP syndrome as well. CONCLUSION: The fast NAT acetylator status, which may result in altered NAT detoxification capacity, is associated with preeclampsia.

Oxidative stress and preeclampsia: rationale for antioxidant clinical trials.

Preeclampsia remains a frequent and potentially dangerous complication of pregnancy. The cause remains largely unknown, but oxidative stress and a generalized inflammatory state are features of the maternal syndrome. The placenta appears to be the principal source of free radical synthesis but maternal leukocytes and the maternal endothelium are also likely contributors. Recent reports have suggested an important role for placental trophoblast NAD(P)H oxidase in free radical generation in preeclampsia. The antioxidant vitamin E is now known to have multiple actions in addition to prevention of lipid peroxidation (ie, inhibition of NAD(P)H oxidase activation and the inflammatory response). In view of the abnormally low plasma vitamin C concentrations in preeclampsia, a combination of vitamins C and E is a promising prophylactic strategy for prevention of preeclampsia. Several multicenter randomized clinical trials are now underway. The potential use of antioxidants and the recognized, albeit modest, benefit of low-dose aspirin prophylaxis have heightened the need for a reliable predictive test for preeclampsia. A combination test involving several relevant biomarkers is likely to provide the best predictive potential.

Effects of oral N-acetylcysteine on plasma homocysteine and whole blood glutathione levels in healthy, non-pregnant women.

Oral N-acetylcysteine supplementation in nine young healthy females induced a quick and highly significant decrease in plasma homocysteine levels and an increase in whole blood concentration of the antioxidant glutathione. N-acetylcysteine impresses as an efficient drug in lowering homocysteine concentration and might be beneficial for individuals with hyperhomocysteinemia who are at increased risk of cardiovascular disease.

Low plasma levels of oxidized low density lipoprotein in preeclampsia.

BACKGROUND: Markers of lipid peroxidation are commonly used to assess oxidative stress in preeclampsia. The aim of this study was to assess the concentration of oxidized low density lipoprotein (oxLDL), a novel marker for lipid peroxidation, and that of the thiobarbituric acid reactive substances (TBARS) in the pathogenesis of severe preeclampsia and to investigate the influence of gestational age on these parameters. METHOD: Plasma levels of oxLDL and TBARS were assayed in women with severe preeclampsia (n = 40), normotensive pregnant controls matched for gestational age (n = 24) and normotensive pregnant controls at full term (n = 16). RESULTS: Women with preeclampsia showed lower oxLDL levels (mean +/- SE) than matched controls (181 +/- 12 vs. 219 +/- 14; p = 0.027), whereas no differences were found for the TBARS concentration (3.8 +/- 0.6 vs. 3.7 +/- 0.4). When women with preeclampsia were compared to control women at full term, TBARS were elevated (3.8 +/- 0.6 vs. 1.5 +/- 0.2; p = 0.01). However, in women with normotensive pregnancy TBARS were also lower in full-term control pregnancy compared to early third-trimester values (p < 0.0001). CONCLUSION: Plasma TBARS decreased during the third trimester of pregnancy, underlining the importance of matching for gestational age when studying markers of lipid peroxidation in pregnant women. Women with preeclampsia had lower plasma levels of oxLDL compared to gestational age-matched controls, indicating that oxLDL could be a marker for preeclampsia.

Thiol status and antioxidant capacity in women with a history of severe pre-eclampsia.

OBJECTIVE: To investigate a possible mechanism that could lead to the subsequent development of cardiovascular diseases (CVD) in women with a history of severe pre-eclampsia. DESIGN: Case-control study. SETTING: University Medical Centre Nijmegen, The Netherlands. SAMPLE: Non-pregnant women with a history of severe pre-eclampsia (n= 131) and women with an uncomplicated obstetric history (n= 94). METHODS: Total plasma levels of cysteine (tCys), homocysteine (tHcy), cysteinylglycine (tCysGly) and glutathione (tGSH), the free-to-oxidised ratio of these thiols in whole blood, the glucose-6-phosphate dehydrogenase (G6PDH) enzyme activity and antioxidant capacity were assessed at least 6 months following last pregnancy. MAIN OUTCOME MEASURE: Oxidative stress and antioxidant status. RESULTS: Women with a history of severe pre-eclampsia showed higher levels (mean [SD]) of tHcy (13.1 [5.0] versus 11.5 [4.8] micromol/L; P= 0.018) and tCysGly (37.5 [5.6] versus 34.0 [5.8] micromol/L; P= 0.0001) compared with controls, whereas tCys was lower (232 [31] versus 242 [39]; P= 0.029). The lower free-to-oxidised ratio of homocysteine (2.3 [0.8] versus 2.9 [1.0], P= 0.0001) among women with a history of severe pre-eclampsia as compared with control subjects might indicate a higher oxidant status for homocysteine. Previous severe pre-eclamptic patients had also a higher antioxidant capacity as compared with controls (0.79 [0.14] versus 0.74 [0.11] mmol Fe2+/L, P= 0.002). CONCLUSION: Since women with a history of severe pre-eclampsia showed elevated total homocysteine levels, which is an independent risk factor for CVD, and higher oxidised homocysteine levels in whole blood, these women may have an enhanced risk for the subsequent development of cardiovascular-related problems in later life.

N-acetylcysteine restores nitric oxide-mediated effects in the fetoplacental circulation of preeclamptic patients.

OBJECTIVE: Preeclampsia is associated with an imbalance between oxidants and antioxidants, resulting in reduced effects of the endothelium-derived, relaxing-factor nitric oxide (NO). Antioxidants, like N-acetylcysteine (NAC), remove reactive oxygen species, resulting in an improvement of endothelial function. We aimed to investigate the effect of NAC on the NO-pathway in the human fetoplacental circulation in preeclampsia and control pregnancies. STUDY DESIGN: The NO-pathway was investigated by use of the NO-synthase inhibitor L-NAME in an ex vivo cotyledon perfusion model. RESULTS: At baseline, fetoplacental arterial pressure was comparable in preeclamptic pregnancies (n=8) and control pregnancies (n=8), and increased dose-dependently after L-NAME. The maximal L-NAME-induced rise in fetoplacental arterial pressure was attenuated in preeclamptic versus control pregnancies (20.8 +/- 2.0 mm Hg vs 36.7 +/- 3.5 mm Hg, P<.05). Addition of NAC increased the L-NAME-induced rise in fetoplacental arterial pressure to 36.4 +/- 3.4 mm Hg in preeclampsia pregnancies (P<.05) and to 49.2 +/- 2.6 mm Hg in control pregnancies (P<.05). CONCLUSION: Preeclampsia is associated with a dysfunction of the NO-pathway. N-acetylcysteine increases NO-mediated effects in the fetoplacental circulation in preeclamptic placentas as well as in healthy control placentas.

Umbilical glutathione levels are higher after vaginal birth than after cesarean section.

Glutathione plays an important role in quenching reactive oxygen species, resulting in oxidation of glutathione, which in times of prolonged oxidative stress may be excreted from the erythrocyte. We investigated arterial and venous umbilical cord levels of glutathione in neonates born by vaginal delivery (n = 140) or cesarean section (n = 38). In a subset of neonates who were delivered vaginally maternal levels were assessed in parallel (n = 14). Median (5th-95th percentile) glutathione levels in venous and arterial umbilical samples were higher after vaginal delivery as compared to cesarean section, 2.7 (0.9-7.3) versus 2.0 (0.6-11.5; P < 0.03) and 3.5 (0.6-22.7) versus 2.3 (0.7-24.3) micromol/L (P < 0.02), respectively. Maternal glutathione levels were higher, 7.8 (4.3-10.6) micromol/L, than corresponding venous (P < 0.001) or arterial (P < 0.02) umbilical levels. These results suggest that vaginal delivery is associated with more oxidative stress than delivery by cesarean section.

The Tyr113His polymorphism in exon 3 of the microsomal epoxide hydrolase gene is a risk factor for perinatal mortality.

BACKGROUND: A genetic predisposition to impaired detoxification of oxidative or chemical stress could play a role in the etiology of perinatal mortality. In this pilot study we investigated the risk of perinatal mortality in relation to genetic polymorphism in microsomal epoxide hydrolase (EPHX) and glutathione S-transferase P1 (GSTP1) in women who experienced perinatal mortality caused by placental pathology, congenital disorders and complications of premature delivery and their male partners. METHODS: Genomic DNA of couples (72 females and 46 males) with a history of perinatal mortality and control couples (71 females and 66 males) with no complications in their obstetric history were analyzed for the presence of the polymorphisms in exon 3 of EPHX (Tyr113His) and GSTP1 (Ile105Val). RESULTS: A similar distribution of the GSTP1 polymorphism was found in all subjects investigated. In women who experienced perinatal mortality, we demonstrated a higher prevalence of the EPHX His113/His113 genotype, which could result in a lower enzyme activity, compared with controls (25% vs. 9%; chi2 = 5.7 and p < 0.02), with an odds ratio (95% confidence interval) of 3.5 (1.1-12.7). CONCLUSION: Our results suggest that the maternal Tyr113His polymorphism in EPHX may be a risk factor for perinatal mortality. However, more research is needed to determine the implication of this finding.

N-Acetylcysteine improves the disturbed thiol redox balance after methionine loading.

Methionine loading seems to be accompanied by increased oxidative stress and damage. However, it is not known how this oxidative stress is generated. We performed the present crossover study to further elucidate the effects of methionine loading on oxidative stress in the blood of healthy volunteers, and to examine possible preventative effects of N -acetylcysteine (NAC) administration. A total of 18 healthy subjects were given two oral methionine loads of 100 mg/kg body weight, 4 weeks apart, one without NAC (Met group), and one in combination with supplementation with 2x900 mg doses of NAC (Met+NAC group). Blood samples were collected before and 2, 4, 8 and 24 h after methionine loading for measurements of thiol levels, protein carbonyls, lipid peroxidation, cellular fibronectin and ferric reducing ability of plasma (FRAP; i.e. antioxidant capacity). After methionine loading, whole-blood levels of free and oxidized cysteine and homocysteine were increased in both groups. Furthermore, the total plasma levels of homocysteine were higher, whereas those of cysteine were lower, after methionine loading in both groups. Lower levels of oxidized homocysteine and a higher free/oxidized ratio were found in the Met+NAC group compared with the Met group. Although the antioxidant capacity decreased after methionine loading, no major changes over time were found for protein carbonyls or cellular fibronectin in either group. Our results suggest that methionine loading may initiate the generation of reactive oxygen species by the (auto)-oxidation of homocysteine. In addition, supplementation with NAC seems to be able to partially prevent excessive increases in the levels of homocysteine in plasma and of oxidized homocysteine in whole blood, and might thereby contribute to the prevention of oxidative stress.