Neil S. Harris

The ADVIA 2120 hematology system: flow cytometry-based analysis of blood and body fluids in the routine hematology laboratory.

The ADVIA 2120 Hematology System was recently released by Bayer HealthCare, Diagnostics Division, as a bench-top analyzer designed for medium- to large-volume laboratories. This flow cytometry-based system uses light scatter, differential white blood cell (WBC) lysis, and myeloperoxidase and oxazine 750 staining to provide a complete blood cell count, a WBC differential, and a reticulocyte count. A cyanide-free method is used to measure hemoglobin colorimetrically. The system is automation ready; in addition to its capability for analyzing peripheral blood specimens, the analyzer is also equipped to analyze cerebrospinal fluid samples. In this article we explain the underlying technology of the ADVIA 2120, provide linearity ranges, method-specific reference ranges, and stability data, and describe novel parameters and applications that are unique to the methodology used by this instrument. Finally, we discuss research applications and future directions, such as the use of this hematology analyzer in the determination of fetal lung maturity.

The Molecular Biology of Human Iron Metabolism

Iron is one of the most important nonorganic substances that make life possible. Iron plays major roles in oxygen transport (eg, hemoglobin; -67% of total body iron [TBI]), short-term oxygen storage (eg, myoglobin; -3.5% of TBI), and energy generation (eg, cytochromes; -3% of TBI). Iron also serves vital roles in various nonheme-containing enzymes (-2% of TBI). Figure 1 lists heme-containing and nonheme iron-containing proteins. TBI is controlled by the rate of iron absorption; there are no physiologic mechanisms to excrete excess iron. Iron deficiency has many adverse consequences, including anemia, and in children, behavioral and learning disorders. Iron excess is toxic to the body, harming the heart, liver, skin, pancreatic islet beta cells, bones, joints, and pituitary gland. Maintaining proper iron balance is essential for maintaining homeostasis and health. TBI in adults normally ranges between 3.5 and 5.0 g. A total of 75% of TBI is functional, and 25% is stored within cells as ferritin or hemosiderin. Ferritin contains 24 subunits of light chains (L chains; 19.7 kDa) and heavy chains (H chains; 21.1 kDa). The L chains are encoded on chromosome 19q13.33 and are 175 amino acids long. The H chains are encoded on chromosome 11q1 and are 183 amino acids long. Each ferritin molecule can contain as many as approximately 4500 ferric ions. Because the major role of iron is in hemoglobin synthesis, this review will focus on iron, iron transport, and hematopoiesis.

Activated Partial Thromboplastin Time Versus Antifactor Xa Heparin Assay in Monitoring Unfractionated Heparin by Continuous Intravenous Infusion

Background: Unfractionated heparin (UFH) has been used clinically for 5 decades. Despite being a cornerstone of anticoagulation, UFH is limited by its unpredictable pharmacokinetic profile, which makes close laboratory monitoring necessary. The most common methods for monitoring UFH are the activated partial thromboplastin time (aPTT) and antifactor Xa heparin assay (anti-Xa HA), but both present challenges, and the optimal method to monitor UFH remains unclear. Objective: To compare the performance of the aPTT with the anti-Xa HA for efficiency and safety of monitoring intravenous UFH infusions. Methods: This was a single-center, retrospective, observational cohort study conducted in an 852-bed academic medical center. Results: One hundred patients receiving intravenous UFH for a variety of indications were enrolled in the study; 50 were assigned to each group. The mean (SD) time to achieve therapeutic anticoagulation was significantly less in the anti-Xa HA group compared with the aPTT group (28 [16] vs 48 [26] hours, p < 0.001). In addition, a greater percentage of anti-Xa HA patients compared to aPTT patients achieved therapeutic anticoagulation at 24 hours (OR 3.5; 95% CI 1.5 to 8.7) and 48 hours (OR 10.9; 95% CI 3.3 to 44.2). Patients in the anti-Xa HA group also had more test values within the therapeutic range (66% vs 42%, p < 0.0001). A significant difference was seen between the 2 groups in the number of aPTT or anti-Xa HA tests performed per 24 hours (p < 0.0001) and number of infusion rate changes per 24 hours (p < 0.01), both favoring the anti-Xa HA group. Conclusions: Monitoring intravenous UFH infusions with the anti-Xa HA, compared to the aPTT, achieves therapeutic anticoagulation more rapidly, maintains the values within the goal range for a longer time, and requires fewer adjustments in dosage and repeated tests.

Type 1 diabetes islet autoantibody markers.

The diagnosis of type 1 diabetes versus other forms of diabetes such as type 2 diabetes is paramount to guiding proper therapy. Several islet autoantibodies have been identified that serve to diagnose immune-mediated, type 1a diabetes in clinically ambiguous cases. These autoantibodies also serve to predict type 1 diabetes in nondiabetic individuals. The most useful islet autoantibodies include islet cell cytoplasmic autoantibodies, insulin autoantibodies, glutamic acid decarboxylase autoantibodies, and insulinoma-associated-2 autoantibodies. Once type 1 diabetes can be safely and reliably prevented, large-scale islet autoantibody screening programs of the general pediatric population may be warranted. It is controversial whether islet autoantibodies influence the course of type 1 diabetes following diagnosis.

The Use of Anti-Xa Assay to Monitor Intravenous Unfractionated Heparin Therapy

Continuous infusion unfractionated heparin (UH) has traditionally been monitored using the activated partial thromboplastin time (aPTT). The use of this test to monitor heparin therapy is not based on randomized controlled clinical trials, and the test is associated with significant intra- and inter-patient variability that is not related to circulating blood heparin activity. Due to these and other limitations, the use of aPTT alone to monitor UF has been questioned. Many laboratories are now transitioning to monitoring actual heparin activity (by anti-factor Xa analysis). In this review, we discuss the limitations of using the aPTT to monitor UH therapy and additionally the limitations of solely using heparin activity to monitor therapy. We also include a discussion of the challenges with monitoring heparin therapy in the pediatric population.

Blood Glucose Measurement in the Intensive Care Unit: What is the Best Method?

Abnormal glucose measurements are common among intensive care unit (ICU) patients for numerous reasons and hypoglycemia is especially dangerous because these patients are often sedated and unable to relate the associated symptoms. Additionally, wide swings in blood glucose have been closely tied to increased mortality. Therefore, accurate and timely glucose measurement in this population is critical. Clinicians have several choices available to assess blood glucose values in the ICU, including central laboratory devices, blood gas analyzers, and point-of-care meters. In this review, the method of glucose measurement will be reviewed for each device, and the important characteristics, including accuracy, cost, speed of result, and sample volume, will be reviewed, specifically as these are used in the ICU environment. Following evaluation of the individual measurement devices and after considering the many features of each, recommendations are made for optimal ICU glucose determination.

Intravenous fluids cause systemic bias in a conductivity-based point-of-care hematocrit meter

BACKGROUND: Point-of-care (POC) devices measuring hematocrit rely on determination of electrical conductivity of whole blood. We hypothesized that some frequently administered IV fluids independently alter blood conductivity and confound hematocrit determination. METHODS: Whole human blood was diluted to predetermined hematocrit values with normal saline, lactated Ringer solution, hetastarch, or plasma. Electrical conductivity and hematocrit (i-STAT® and spun methods) were measured at each dilution. In separate experiments, the effects of propofol and heparin were noted on these variables. RESULTS: Greater dilution significantly increased conductivity irrespective of diluent type. The magnitude of the conductivity slopes increased in order for plasma, hetastarch, lactated Ringer solution, and normal saline dilution. Moreover, each slope varied from every other slope (all P < 0.0001), and 94.2% of hematocrit values measured by i-STAT (n = 211 of 224) were less than those for the spun method. Dilution with plasma, normal saline, lactated Ringer solution, and hetastarch caused bias (Bland-Altman limits of agreement) of −2.7% (−6.9/1.4), −4.6% (−7.3/−2.0), −4.8% (−7.8/−1.7), and −2.0% (−5.6/1.9), respectively. The Cohen &kgr; agreement values (5th–95th confidence interval) for a transfusion trigger of 30% were 0.90 (all values, 0.85–0.95), 0.25 (hematocrit <30%, 0.02–0.48), and 0.21 (hematocrit 18%–30%, 0.01–0.42). Clinically relevant concentrations of propofol and heparin had minimal effects on electrical conductivity or hematocrit determination. CONCLUSIONS: Dilution of blood with frequently used IV solutions affects whole blood conductivity determinations and thereby decreases hematocrits measured by a POC device relying on this method as compared with spun hematocrit. Conductivity-based hematocrit POC devices should be cautiously interpreted when hemodilution is present.

Type 2B von willebrand disease associated with the release of platelet agglutinates from megakaryocytes in the bone marrow

We report a child with thrombocytopenia since birth, circulating platelet agglutinates, and a tendency to bleed. A bone marrow aspirate revealed large platelet clumps within the bone marrow and megakaryocyte nuclei surrounded by halos of clumped platelets. Laboratory evaluation revealed type 2B von Willebrand disease. Gene sequencing revealed a G to C mutation at base 3923 of the VWF gene. This mutation was previously described in a family with circulating platelet clumps and abnormal megakaryopoiesis with release of clumped platelets in culture. This same mutation was previously described in a family with circulating platelet aggregates and abnormalities of platelet release from megakaryocytes in vitro. Presence of megakaryocytes with halos of clumped platelets in our patient suggests that platelet agglutinate occurs in the bone marrow in some type 2B von Willebrand disease patients.

Susceptibility of commonly used ferritin assays to the classic hook effect

*Corresponding author: Dina N. Greene, Department of Laboratory Medicine, University of Washington, Seattle, WA, 98195, USA, Phone: +1 206 5987549, E-mail: dngreene@uw.edu Pratistha Ranjitkar: Department of Laboratory Medicine, University of Washington, Seattle, WA, USA Cameron J. Turtle: Fred Hutchinson Cancer Research Center, Seattle, WA, USA; and Department of Medicine, University of Washington, Seattle, WA, USA Neil S. Harris: Department of Pathology, University of Florida, Gainesville, FL, USA Daniel T. Holmes: Department of Pathology and Laboratory Medicine, St. Paul’s Hospital, Vancouver, BC, Canada; and Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada Amy Pyle-Eilola: Nationwide Children’s Hospital, Columbus, OH, USA David G. Maloney: Fred Hutchinson Cancer Research Center, Seattle, WA, USA; Department of Medicine, University of Washington, Seattle, WA, USA; and Seattle Cancer Care Alliance, Seattle, WA, USA Letter to the Editor

Nitrous Oxide Abuse and Vitamin B12 Action in a 20-Year-Old Woman: A Case Report

Herein, we report a case of a 20-year-old (ethnicity not reported) woman with a history of nitrous oxide abuse and clinical symptoms consistent with spinal cord subacute combined degeneration with associated low serum concentrations of vitamin B12, elevated methylmalonic acid levels, and radiologic evidence of demyelination of the dorsal region of the spinal column. The health of the patient improved dramatically with B12 supplementation. In this case, we discuss the interaction of nitrous oxide with the enzymatic pathways involved in the biochemistry of vitamin B12.