Red cell mass and plasma volume measurements in polycythemia: evaluation of performance and practical utility.

BACKGROUND: Despite the absence of any systematic evidence for diagnostic utility, red cell mass (RCM) measurement has been endorsed as a major diagnostic criterion for polycythemia vera (PV) based on a set of eligibility criteria for a clinical trial formulated by an International PV Study Group in 1967. METHODS: A retrospective analysis was performed on a consecutive series of 105 patients who underwent blood volume measurements for evaluation of polycythemia. In a previous study, the authors had systematically compared RCM measurement by 51Cr-labeled erythrocytes and 125I-labeled human serum albumin and demonstrated equivalence between the two methods. In the current study, they used the latter method and applied the International Committee for Standardization in Haematology recommendations for result interpretation in order to evaluate test performance and practical utility. RESULTS: RCM exceeded the 98-99% limits of the reference range in 76%, 20%, 22%, and 57% of patients with PV (n = 25), secondary polycythemia (n = 35), spurious or apparent polycythemia (n = 38), and essential thrombocythemia (n = 7), respectively. Decreased plasma volume was rarely seen in any of the disease categories. In all instances of PV, the diagnosis was readily apparent, based on alternative clinical and laboratory tests, and did not require the additional information from blood volume measurement. Furthermore, alternative methods of PV diagnosis, based on disease-specific biological markers as well as bone marrow histology, are now available. CONCLUSIONS: The continued use of RCM and plasma volume measurements for the diagnosis of PV is no longer warranted.

Erythrocytosis due to bisphosphoglycerate mutase deficiency with concurrent glucose-6-phosphate dehydrogenase (G-6-PD) deficiency.

A 28-year-old asymptomatic male of Iranian Jewish (Meshadi) heritage was found on routine exam to have an erythrocytosis (RBC = 6.22 x 10(12)/l, Hgb = 19.2 g/dl, Hct = 58.9%). Splenomegaly was absent on physical exam. There was no family history of erythrocytosis. His oxygen dissociation curve was left-shifted with a p50 of 19 mmHg (normal = 25-32 mmHg). Hemoglobin electrophoresis showed no abnormalities. DNA sequencing of the hemoglobin beta globin gene and both alpha globin genes did not reveal a mutation. A 2,3-bisphosphoglycerate (BPG) level was markedly decreased at 0.3 micromol/g Hb (normal = 11.4-19.4 micromol/g Hb). The patient's bisphosphoglycerate mutase (BPGM) enzyme activity was also markedly decreased at 0.16 IU/g Hb (normal = 4.13-5.43 IU/g Hb). A red cell enzyme panel revealed a markedly decreased G-6-PD level (0.3 U/g Hb, normal = 8.6-18.6 U/g Hb). His parents and a brother were also available for evaluation. Both parents showed normal 2,3-BPG levels but BPGM activity approximately 50% of normal. Paradoxically, the brother showed normal BPGM activity but a slightly decreased 2,3-BPG level. All family members had markedly decreased G-6-PD activity. DNA sequencing of the BPGM gene showed the propositus to be homozygous for 185 G-->A, Arg 62 Gln in exon 2. Thus, the erythrocytosis in this patient is secondary to low 2,3-BPG levels, due to a deficiency in BPG mutase. This appears due to consanguinity within this family.

Flow cytometric measurement of hemoglobin F in RBCs: diagnostic usefulness in the distinction of hereditary persistence of fetal hemoglobin (HPFH) and hemoglobin S-hPFH from other conditions with elevated levels of hemoglobin F.

The cellular distribution of hemoglobin F is important for evaluating persistently elevated hemoglobin F levels, such as in hereditary persistence of fetal hemoglobin (HPFH) or delta/beta-thalassemia, and for differentiating homozygous hemoglobin S (or hemoglobin S-beta(0)-thalassemia) from hemoglobin S-HPFH, traditionally done by using the Kleihauer-Betke (K-B) acid elution test. We evaluated a flow cytometric method using an anti-hemoglobin F antibody as a replacement for the K-B test. We used 172 specimens representing a variety of conditions: HPFH trait, 19 cases; delta/beta-thalassemia trait, 8 cases; hemoglobin S-HPFH, 10 cases. By flow cytometry, all cases of HPFH trait gave a hemoglobin F pattern comparable to the homocellular pattern obtained by the K-B test; all cases of delta/beta-thalassemia tested gave a pattern comparable to a K-B heterocellular pattern. Most cases of hemoglobin S-HPFH gave a homocellular distribution of hemoglobin F whereas all cases of homozygous hemoglobin S with elevated hemoglobin F levels gave a heterocellular pattern. Flow cytometry provides a more rapid and objective method for assessing cellular distribution of hemoglobin F and is useful for patient evaluation when HPFH trait, delta/beta-thalassemia trait, or hemoglobin S-HPFH trait is suspected.

Recognition and management of hereditary hemochromatosis.

Hereditary hemochromatosis is the most common inherited single-gene disorder in people of northern European descent. It is characterized by increased intestinal absorption of iron, with deposition of the iron in multiple organs. Previously, the classic description was combined diabetes mellitus, cutaneous hyperpigmentation and cirrhosis. Increasingly, however, hereditary hemochromatosis is being diagnosed at an earlier, less symptomatic stage. The diagnosis is based on a combination of clinical, laboratory and pathologic findings, including elevated serum transferrin saturation. Life expectancy is usually normal if phlebotomy is initiated before the development of cirrhosis or diabetes mellitus. Hereditary hemochromatosis is associated with mutations in the HFE gene. Between 60 and 93 percent of patients with the disorder are homozygous for a mutation designated C282Y. The HFE gene test is useful in confirming the diagnosis of hereditary hemochromatosis, screening adult family members of patients with HFE mutations and resolving ambiguities concerning iron overload.

Myeloproliferative Disease: Polycythemia Vera: The Packed Cell Volume and The Curious Logic of The Red Cell Mass.

Since the first systematic blood volume studies of polycythemia in the 1920s, measurement of blood volume and red cell mass (RCM) has become routine. However, the radionuclide-labeling methods promulgated by the International Committee for Standardization in Haematology (ICSH) remain complex and poorly understood. Many hematologists and other clinicians err in the belief that these methods permit "direct measurement" of RCM, whereas the ICSH method is indirect: it requires calculation of RCM from (PCV) x (whole blood volume). The use of an elevated value of PCV to calculate RCM in order to evaluate the same elevated value of PCV is a curiously circular logic that is embraced by most clinicians and most hematologists. Analysis of published data in 186 cases of polycythemia vera indicates that RCM is an exponential function of PCV. In most cases, PCV alone suffices to document normal or increased RCM. Relative polycythemia results from dehydration, not from stress. Clinicians need to be aware of the range of physiologic fluctuations that normally occur in plasma volume. Realistic criteria for normal ranges of PCV, Hb concentration and RCM should be adopted in clinical laboratories so that clinicians will not be misled to undertake futile and costly investigations of results that are in the upper percentiles of the normal distribution, as exemplified by the Ulysses Syndrome.