Laboratory Assessment of Anemia

Anemia is one of the most common health problems in both industrialized and developing countries. It has been recognized by the World Health Organization as an important disorder leading to significant health care burden. Laboratory testing plays a significant role in the diagnosis of most types of anemia since the clinical diagnosis may not always be straightforward, especially with multiple underlying conditions. Once the existence of anemia is established, the cause must be determined to enable selection of a specific and effective therapy. Various hematologic parameters and biochemical tests can be used in combination with patient clinical history to identify the most likely causes of anemia.

Homocysteine, iron and cardiovascular disease: a hypothesis

Elevated circulating total homocysteine (tHcy) concentrations (hyperhomocysteinemia) have been regarded as an independent risk factor for cardiovascular disease (CVD). However, several large clinical trials to correct hyperhomocysteinemia using B-vitamin supplements (particularly folic acid) have largely failed to reduce the risk of CVD. There is no doubt that a large segment of patients with CVD have hyperhomocysteinemia; therefore, it is reasonable to postulate that circulating tHcy concentrations are in part a surrogate marker for another, yet-to-be-identified risk factor(s) for CVD. We found that iron catalyzes the formation of Hcy from methionine, S-adenosylhomocysteine and cystathionine. Based on these findings, we propose that an elevated amount of non-protein-bound iron (free Fe) increases circulating tHcy. Free Fe catalyzes the formation of oxygen free radicals, and oxidized low-density lipoprotein is a well-established risk factor for vascular damage. In this review, we discuss our findings on iron-catalyzed formation of Hcy from thioethers as well as recent findings by other investigators on this issue. Collectively, these support our hypothesis that circulating tHcy is in part a surrogate marker for free Fe, which is one of the independent risk factors for CVD.

Pathogenesis of A⁻β⁺ ketosis-prone diabetes

A⁻β⁺ ketosis-prone diabetes (KPD) is an emerging syndrome of obesity, unprovoked ketoacidosis, reversible β-cell dysfunction, and near-normoglycemic remission. We combined metabolomics with targeted kinetic measurements to investigate its pathophysiology. Fasting plasma fatty acids, acylcarnitines, and amino acids were quantified in 20 KPD patients compared with 19 nondiabetic control subjects. Unique signatures in KPD--higher glutamate but lower glutamine and citrulline concentrations, increased β-hydroxybutyryl-carnitine, decreased isovaleryl-carnitine (a leucine catabolite), and decreased tricarboxylic acid (TCA) cycle intermediates--generated hypotheses that were tested through stable isotope/mass spectrometry protocols in nine new-onset, stable KPD patients compared with seven nondiabetic control subjects. Free fatty acid flux and acetyl CoA flux and oxidation were similar, but KPD had slower acetyl CoA conversion to β-hydroxybutyrate; higher fasting β-hydroxybutyrate concentration; slower β-hydroxybutyrate oxidation; faster leucine oxidative decarboxylation; accelerated glutamine conversion to glutamate without increase in glutamate carbon oxidation; and slower citrulline flux, with diminished glutamine amide-nitrogen transfer to citrulline. The confluence of metabolomic and kinetic data indicate a distinctive pathogenic sequence: impaired ketone oxidation and fatty acid utilization for energy, leading to accelerated leucine catabolism and transamination of α-ketoglutarate to glutamate, with impaired TCA anaplerosis of glutamate carbon. They highlight a novel process of defective energy production and ketosis in A⁻β⁺ KPD.

Effects of some pre-analytical conditions on the measurement of homocysteine and cysteine in plasma

The association of hyperhomocysteinemia and hypercysteinemia with the risk of arterial and venous thrombosis is well documented. While it is known that standardized pre-analytical conditions are necessary for reliable measurement of plasma total homocysteine, the effects of pre-analytical conditions on cysteine measurement are less well known. The aim of this study was to evaluate the effects of pre-analytical conditions on the measurement of homocysteine and cysteine. We observed that the concentration of total homocysteine in plasma increased significantly with time (38% after 6 h), whereas total cysteine decreased (5% after 2h) when blood anticoagulated with ethylenediaminetetraacetic tripotassium salt was kept at room temperature. These changes were minimized when acidic citrate dextrose was used as an anticoagulant and were abolished when blood samples were immediately placed on crushed ice, independently of the anticoagulant. Storage of plasma for 72h at room temperature induced a small (≅6%), but significant, decrease in cysteine when blood was collected in ethylenediaminetetraacetic tripotassium salt. In contrast, homocysteine was stable in plasma for 72h, independently of the anticoagulant used. In conclusion, if blood samples for plasma total homocysteine and cysteine measurement cannot be kept on ice, they should be collected in acidic citrate dextrose to minimize the artifactual changes.

Homocysteine and pregnancy

Homocysteine is an amino acid that is involved in several key metabolic processes, including the methylation and sulphuration pathways. Blood concentrations of homocysteine are determined by various dietary factors, including folic acid and vitamin B(12), by alteration in physiology, such as renal impairment, and by variation in the activity of enzymes in the various pathways as a result of genetic polymorphisms, some of which are commonly found in the population. Hyperhomocysteinaemia has been associated with vascular disease, although whether it is cause or effect is still a matter of debate. In normal pregnancy, homocysteine concentrations fall. Disturbance of maternal and fetal homocysteine metabolism has been associated with fetal neural tube defects, with various conditions characterized by placental vasculopathy, such as pre-eclampsia and abruption, and with recurrent pregnancy loss. Apart from folate supplementation, which has been clearly shown to halve the risk of fetal neural tube defects, no other strategies have been identified in relation to homocysteine metabolism that will reliably reduce the frequency of these other common obstetric pathologies.

Increased serum homocysteine and sudden death resulting from coronary atherosclerosis with fibrous plaques

INTRODUCTION

Modest elevations of total homocysteine have been associated with increased risk for coronary atherosclerosis but correlation between elevated homocysteine and plaque morphology has not been described in humans.

METHODS

We determined serum homocysteine at postmortem from 87 men with coronary thrombus (62 of whom were diagnosed as acute), from 35 men with severe coronary disease without thrombus, and from 46 controls. In coronary deaths, atherosclerotic plaques at the sites of maximal luminal narrowing of the four epicardial coronary arteries were classified as fibrous plaques, fibrous cap atheromas, thin-cap atheromas, and healed ruptures, and macrophage infiltration was assessed semiquantitatively.

RESULTS

Median serum homocysteine postmortem as a result of acute thrombus was 10.4 micro mol/L (P=0.4 versus controls), 12.1 micro mol/L in men with organized thrombi (P=0.1 versus controls), 15.6 micro mol/L in men without thrombus (P=0.007 versus controls), and 9.8 micro mol/L in controls. The median homocysteine was 12.1 micro mol/L in 65 men with healed infarcts (P=0.03 versus controls). The number of fibrous plaques was associated with log-normalized homocysteine (P=0.004), independent of age, albumin, smoking, hypertension, and serum cholesterol. Homocysteine levels in the upper tertile (>15 micromol/L) were associated with sudden death without acute or organized thrombus (odds ratio 3.8, P=0.03) independent of age and other risk factors; the coexistence of diabetes increased the association (odds ratio 25.1, P=0.009, versus lowest tertile < or =8.5 micromol/L).

CONCLUSIONS

Increased serum homocysteine is associated with sudden death in the absence of acute coronary thrombosis, especially with concomitant diabetes, and with the presence of lipid-poor, fibrous plaques.

Effects of Temperature on Stability of Blood Homocysteine in Collection Tubes Containing 3-Deazaadenosine

Background: The accuracy of homocysteine (Hcy) results is currently compromised by the requirement to separate the plasma within 1 h of sample collection. We studied the effect of temperature on the stability of plasma Hcy over a 72-h time course in blood collected into evacuated tubes containing either EDTA alone or both EDTA and 3-deazaadenosine (3DA).

Methods: We recruited 100 volunteers, including both diseased and healthy individuals with a range of baseline plasma Hcy values, from two centers. Blood samples were collected into tubes containing EDTA, and EDTA plus 3DA and stored at ambient temperature (20–25 °C) or refrigerated (2–8 °C). Aliquots of blood were centrifuged at various times up to 72 h, the plasma was removed, and Hcy was measured by HPLC.

Results: Plasma Hcy measurement covering the sample collection and storage conditions during the whole time course was possible on samples from 59 of those recruited. One-way ANOVA for repeated measures within subjects revealed that only samples that were collected into tubes containing EDTA plus 3DA and stored refrigerated were stable over 72 h (P = 0.2761).

Conclusions: A combination of 3DA and storage at 2–8 °C will allow collection of samples for plasma Hcy measurement outside of the hospital setting and wider population screening.