Measurement Of Red Cell Volume Research Articles

Red cell volume measurement - using indium as a replacement for chromium.

The withdrawal of Cr-chromate has meant that the technique commonly used for direct measurement of red cell volume has had to be replaced. Most centres moved to a Tc erythrocyte label, however, Tc is known to dissociate over time. We have investigated an alternative technique using an In-chloride and tropolone solution and tested this both in vitro and in vivo. Initial in-vitro and in-vivo work, which included a check of the stability of the radio-labelled product at one hour, demonstrated this label to be stable over this time period. To date, 20 patients have undergone this technique and results show that this technique is a viable alternative to Cr-chromate particularly for patients with splenomegaly who require late sampling. This procedure is now in routine use in our institution.

Changes in circulating red cell volume during the first 6 weeks of life in very-low-birth-weight infants

Little is known about the change in circulating red cell volume (RCV) of very-low-birth-weight (VLBW) infants during the first weeks of life. RCV was measured during the first 5 d in 35 VLBW infants using chromium-51 labeling of the infants' red blood cells (RBCs). RCV was measured again at 6 wk of age in 12 infants, and the volumes of RBCs lost by phlebotomy and those gained by transfusion were recorded between the RCV measurements. In six infants, the volume of waste blood on materials contaminated with blood during phlebotomy, which would usually be discarded, was measured by radioactive counting. The mean RCV in the first several days of life was 39.6 ml (35.7 ml/kg; range: 20.1-58.7 ml/kg). Of the 12 infants whose RCV was measured twice, all but one had a decrease in absolute RCV. The mean RCV initially and at 6 wk were 37.3 and 26.6 ml, respectively. The mean volume of RBCs lost through phlebotomy was 29.2 ml, and the mean volume of RBCs given by transfusion was 34.5 ml. During the first 6 wk of life, when the anemia of prematurity is evolving, the RCV falls despite complete replacement of RBCs lost by diagnostic phlebotomy with transfused RBCs.

Comparison of multiple red cell volume methods performed concurrently in premature infants following allogeneic transfusion

Background:Study of the pathophysiology and treatment of anemia of prematurity is facilitated by direct measurement of red cell volume (RCV) utilizing microliter quantities of blood samples. Our objective was to compare concurrent measurements of multiple direct RCV methods in infants.Methods:Eighteen preterm infants receiving clinically-indicated transfusions had concurrent flow cytometric determinations of RCV and 24 h red blood cell (RBC) recovery based on donor-recipient differences of biotin–labeled RBCs (BioRBCs), Kidd antigen mismatched RBCs, and HbF positive (HbF+) RBCs. HPLC was also used to measure HbF and HbA protein concentrations for RCV determination.Results:Concurrent RCV measurements using BioRBCs (18 and 54 μg/ml), Kidd antigen, and HbF flow cytometry were not statistically different compared to RCVs measured using the reference BioRBC density (6 μg/ml). In contrast, the HbF HPLC method over estimated RCV by 45% compared to the reference method. All methods demonstrated 100% 24 h post-transfusion RBC recovery (PTR24).Conclusions:Because BioRBC, Kidd antigen, and HbF flow cytometry are safe and accurate methods requiring <10 μl of patient blood to determine RCV and PTR24 in preterm infants, they can be useful in clinical and research studies of anemia and other conditions.

Red cell indices in classification and treatment of anemias

Measurements of red cell volume, hemoglobin (Hb) concentration and Hb content continue to play a crucial role in the differential diagnosis of anemias 80 years after the publication of Wintrobe's seminal work. Modern hematology analyzers provide additional data on the heterogeneity of these parameters (distribution width) and quantify similar parameters of reticulocytes as well. Red cell and reticulocyte cellular indices are widely used in the diagnosis and monitoring of hematological diseases. Quantification of hypochromic cells is valuable in the differential diagnosis of thalassemia trait and iron deficiency, and in monitoring therapeutic response to erythropoietic stimulating agents, while hyperchromic cells are an essential diagnostic component for hereditary spherocytosis and may correlate with hemolytic parameters in sickle cell disease. Values for these parameters however depend on the technology used. Red cell clearance is associated with a reduction in both Hb content and cell volume: normal cells are likely to be removed by the time they reach a volume of 72 fl. Reticulocyte parameters such as Hb content (CHr or ret-He) or maturity index (RMI) have shown value in a variety of hematological conditions. New findings from genetic association studies have identified several potential novel genes affecting red cell indices, which are not mediated by changes in iron availability. Red cell indices continue to provide an essential support to the diagnosis and monitoring of hematological diseases.

A single measurement with 51Cr-tagged red cells or 125I-labeled human serum albumin in the prediction of fractional and whole blood volumes: an assessment of the limitations

This study investigated variations in the prediction of blood volumes from a single measurement of red cell volume (RCV) with 51Cr or plasma volume (PV) with 125I human serum albumin (HSA). In 111 subjects, fractional and whole blood volumes were estimated from separate direct measurements of RCV and PV. The f ratio (body to venous hematocrit) was also determined. There was a very good correlation between 125I-HSA measured PV (2857 ± 822 ml) and that estimated with 51Cr-tagged red blood cells (2864 ± 747 ml) (r = 0.936, p = 0.000) and also between 51Cr measured RCV (2600 ± 774 ml) and that estimated with 125I-HSA (2589 ± 843 ml) (r = 0.944, p = 0.000). The 95% limits of agreement (mean ± 2SD of differences, relative to the mean of paired data) ranged −0.2% ± 20.3% and 0.4% ± 21.4%, respectively. The 95% prediction intervals of measured from estimated fractional blood volumes spanned ±20.3% and ±19.5%, respectively, relative to the predicted values with regression equations. Proportional degrees of inaccuracy were found in whole blood volume estimations. The f ratio was inconstant and correlated with PV and the body hematocrit. We conclude that blood volumes can be determined reliabily only with direct measurements of RCV and PV. Estimated blood volumes may lead to misconceptions.

Multiple red cell volumes (RCV) can be determined simultaneously and independently in humans in vivo using red cells (RBCs) labeled at 4 biotin densities

Anemia is a common and serious problem in critically ill neonates. To investigate the pathophysiology of anemia and to assess responses to red blood cell (RBC) transfusions and erythropoietin therapy, repeated measurement of RCV and blood volume would be useful. We previously reported the in vivo validation of a nonradioactive method for determination of RCV in adults using flow cytometric enumeration of RBCs labeled at one or two biotin densities. Here we report the simultaneous measurement of RCV in 2 adult subjects using 4 populations of RBCs labeled at distinct biotin densities. In one subject, biotinylation reagent concentrations from 9 to 243 μg/mL of RBC produced a mean RCV of 24 ± 0.6 mL/kg; CV= 3%. In the second subject, biotinylation reagent concentrations from 6 to 192 μg/mL of RBC produced a mean RCV of 29 ± 0.8 mL/kg; CV= 3%. RCV values were not different by ANOVA among the 4 densities for either subject. These studies provide evidence that RBCs biotinylated at discrete densities can be used for simultaneous and repeated independent measurements of RCV in vivo in humans. Because only small sample volumes are required and because the subject is not exposed to radiation, we speculate that this RCV method will be useful in investigating the physiology and pathophysiology of anemia in pregnant women, fetuses, and infants. NIH P01 HL046925; Thrasher Research Foundation 02825‐3.

Red Cell Volume Can Be Accurately Determined in Sheep Using a Nonradioactive Biotin Label

The sheep has served as an informative animal model for investigation of human fetal and newborn erythropoiesis and red blood cell (RBC) kinetics. We previously validated the permanent label (14C)cyanate for measuring red cell volume (RCV) in sheep. Here, we validate biotin labeling of RBCs as a nonradioactive method for measuring RCV in sheep with the anticipation that it can be applied in studies of human infants. The RCV was determined simultaneously using two techniques for quantitation of the biotin label. The first one quantified total blood concentration of biotin label on biotin-labeled RBCs using (125I)streptavidin. The second one enumerated biotin-labeled RBCs by flow cytometry after incubation with fluorescein-conjugated avidin. RCV measurements made using the two biotin quantitation techniques were validated against both (14C)cyanate and 51Cr as reference methods. Both biotin techniques produced RCV values that agreed well with the reference methods and with each other, producing correlation coefficients averaging >or =0.93. Sequential repetitive measurements in the same animal also agreed with the (14C)cyanate method and each other (average difference <10%). These results establish biotin-labeled RBCs as an accurate method for performing RCV measurements in sheep. This biotin method can be applied in studies that model neonatal erythropoiesis.

Prediction of red cell and blood volumes distribution by various nomograms: do current nomograms overestimate?

Currently used formulas for estimation of a person's red cell volume (RCV) by weight and height are decades old and were based on the use of 51Cr isotopes and on a sample population, which may not be reflective of today's population. In this study, the accuracy and precision of the use of 99mTc RCV measurements in volunteers more typical of today's population were evaluated. The subjects were volunteers who met the requirements for a standard blood donation. The mean +/- standard deviation (SD) 99mTc RCV for 127 males (mean weight, 83.2 kg; height, 180 cm) was 2062 +/- 339 mL, and for 101 females (mean weight, 69.5 kg; height, 166 cm) it was 1320 +/- 201 mL. These results were highly correlated with RCV results with the standard extrapolation 51Cr method with stored red blood cells (RBCs) and highly consistent (within +/-10%) by repeated measurements with the same 22 donors over a 3.5-year period. The RCV results correlated with estimates from the current formulas, but were on average 11 to 14 percent lower. The studies demonstrated that 99mTc is a reproducible and precise method for determination of a person's RCV and that current formulas may significantly overestimate the RCV of today's population. This is likely the result of a shift in population characteristics over the past four decades as reflected by an increased mean body mass index (from 25 to 28 kg/m2), which has not resulted in a proportionally increased RCV.

Bedside red cell volumetry by low-dose carboxyhaemoglobin dilution using expiratory gas analysis

We developed a non-invasive, continuous, high-resolution method of measuring carboxyhaemoglobin fraction (COHb%) using expiratory gas analysis (EGA). We assessed whether application of EGA to carboxyhaemoglobin dilution provides red cell volume (RCV) measurement with accuracy equivalent to that of CO-haemoximetry, with a smaller infusion volume of carbon-monoxide-saturated autologous blood (COB). Method. We assessed the agreement between repeated COHb% measurements by EGA and simultaneous measurement by CO-haemoximetry, using Bland and Altman plot, in healthy subjects and patients with artificially controlled ventilation and no radiological evidence of pulmonary oedema or atelectasis. We assessed the agreement between RCV measurements by EGA with infusion of 20 ml of COB (RCVEGA) and RCV measurements by CO-haemoximetry with infusion of 100 ml of COB (RCVHEM), in healthy subjects. The 'limits of agreement' between COHb% measurement by EGA (1 min average) and CO-haemoximetry were -0.09 and 0.08% in healthy subjects, and -0.11 and 0.09% in patients. Given the resolution of CO-haemoximetry (0.1%), the accuracy of EGA was equivalent to or greater than that of CO-haemoximetry. The 'limits of agreement' between RCVEGA and RCVHEM were -0.14 and 0.15 litre. Given the average resolution of RCVHEM (0.14 litre), the accuracy of RCVEGA was equivalent to that of RCVHEM. EGA provided non-invasive, accurate, continuous, high-resolution COHb% measurements. Applying EGA to carboxyhaemoglobin dilution, we achieved RCV measurements with accuracy equivalent to that of CO-haemoximetry, with one-fifth of the COB infusion volume. However, clinical application of the method is limited to patients with no radiological evidence of pulmonary oedema or atelectasis.

Measured hematocrit:Does it reflect measured red cell volume?

Introduction: Hematocrit is a ratio of red cell volume to plasma volume and has been used as a surrogate marker for red cell volume as well as to determine blood transfusions. Patients may tolerate lower hematocrits if the plasma volume is normal, while hypovolemic anemia may lead to poor outcome. It is unclear whether measured hematocrit reflects red cell volume without information regarding plasma volume. Technique for measurement of plasma volume and RBC mass has been cumbersome until improved technology has made it clinically useful. This study was done in surgical intensive care unit patients where hematocrit was compared to a corrected hematocrit calculated from blood volume measurement results using a blood volume analyzer (BVA-100, Daxor, New York). Methods: Consecutive surgical ICU patients whose volume status was deemed uncertain by the treating team had blood volume measurements performed utilizing 5 blood sample draws after albumin I-131 radioisotope injection. Plasma volume was measured and the red cell volume was calculated from the measured hematocrit. A corrected hematocrit was calculated from the measured volume. Corrected hematocrit is defined as what the hematocrit would be if the patient had normal whole blood volume. This study compared measured hematocrit to corrected hematocrit using the Bland and Altmann analysis. Results: 42 patients completed the study with 84 simultaneous blood volume and hematocrit measurements. Average age was 61 ± 20 years with 7 females:35 males. APACHE II score was 20 ± 6 and the mortality rate was 5/42 (12%). There were 15 trauma victims, 21 General Surgery patients, and 6 from other surgical subspecialties with the following problems: 12 with septic shock/severe sepsis, 8 with hemorrhaghic shock, 22 with respiratory failure. The measured hematocrit was lower than the corrected hematocrit in 38 instances (45%), higher in 17 readings (29%) and equivalent (defined as ±3% of each other) in 28 (33%) measurements. The Bland and Altmann analysis showed a mean difference between measurements (bias) of 3.4 ± 7.8 hematocrit percentage points with a 95% Confidence Interval of 1.7 to 5.1. The precision (error) was 15.2 hematocrit percentage points. Conclusion: Measured hematocrit may not reflect true red cell volume in the surgic al ICU patients and may be incorrect as much as 15 percentage points. There is a sub-set of patients who are hypovolemic. Such patients, when their hematocrit is “adjusted or normalized” to normal volume, are significantly more anemic than evidenced by their peripheral hematocrit. Contrary wise, there is a significant percentage of patients who are hypervolemic and whose hematocrit when normalized to true volume status, are shown to be not anemic and who should not receive transfusions. There are patients who should receive transfusions who can only be recognized by blood volume measurement, specifically red cell volume measurement, and another group of patients who are volume-expanded and hemodiluted and who may receive inappropriate transfusions.

A review of methodology and normal ranges for the estimation of red cell and plasma volume

Aim The aim of this study was to audit current procedures for the measurement of red cell volume (RCV) and plasma volume (PV) against ICSH (International Council for Standardisation in Haematology) guidelines. Method Eighty-nine measurements of RCV and PV were categorized according to three normal ranges: (1) Retzlaff's height and weight formula; (2) weight only formula; and (3) ICSH recommendations. Results Twelve patients who had a raised RCV using Retzlaff's formula fell into the ICSH normal range. Clinical follow-up has so far been obtained on seven of these patients; all were treated conservatively. Categorization of RCV by weight only formula differed from the ICSH method in 21 cases. In 14 patients with a BMI>29 kg·m−2 there was a difference between the two methods in 9 (64%) cases. Departures from the ICSH recommendations for blood sampling, resulting in an error of 5% in measured PV, and differences in the correction factors applied at the two hospitals were also investigated. Weight only based normal ranges under-diagnose polycythemia in obese subjects whilst both the Retzlaff and ICSH ranges appear to be independent of obesity. Patients diagnosed as having a raised RCV using the Retzlaff formula who were within the ICSH normal range were treated conservatively, suggesting that the Retzlaff range is too narrow. Conclusion This study demonstrates the importance of reviewing established procedures against current standards.

The measurement of blood volume--state-of-the-art

The term blood volume (BV) measurement can be understood as the exact volumetric definition of both components of blood, the red cell volume (RCV) and the plasma volume (PV) using tracer dilution methods. The tracer used to measure the RCV must be bound to the erythrocytes and for the PV to plasma proteins, in order to label the distribution space of each carrier (i.e. erythrocytes and albumin molecules). To differentiate this there are indirect methods to estimate the BV, such as measurement of the diastolic pressure or transoesophageal echocardiography, which will not be discussed here. Alterations in the RCV and PV cannot be routinely measured, or at most only roughly estimated by means of the haematocrit (Hc) or haemoglobin (Hb) concentration which can lead to serious errors when large changes have occurred. At present measurements of the RCV and PV are not carried out in routine clinical practice. The introduction of nonradioactive tracers with a faster elimination now renders possible a relatively exact measurement of both volumes under certain clinical situations, albeit with a high technical outlay. The RCV is measured using the tracer sodium fluorescein (SoF) and the PV with the dye indocyanine green (ICG). The RCV measurement seems to be suitable for certain clinical situations, such as characterization of the preoperative condition of a patient or quantification of surgical blood loss after an operation, because it is less invasive and has a high precision. However, the results of the RCV measurement can only be delivered after 1 h which makes it more suitable for clinically stable situations. In contrast the PV estimation is based on the measurement of the ICG concentration in the arterial bloodstream after a bolus injection of the dye in the central veins and is used more in intensive care because of the invasivity. The results can be obtained 5 min after injection of the dye and therefore even rapid changes in the PV can be monitored.

Determination of red cell volume in infants needing blood transfusion.

The total circulating red cell volume (RCV) is a better guide to the oxygen-carrying capacity of the blood in the whole circulation than is the haemoglobin concentration (Hb) or haematocrit in a blood sample. Pre- and post-transfusion RCV (and blood volume (BV)) may be determined by flow cytometry by exploiting antigen differences between transfused donor red cells and the recipient's red cells. This paper describes the use of red cell antigen differences of Duffy, Kidd, MN and RhD between donor and recipient. In 20 infants, transfused on 21 occasions, pretransfusion RCV ranged from 12 to 39 mL kg(-1) body weight. Only at one transfusion could no usable donor-recipient antigen differences be exploited. Measurement of RCV, used routinely, may determine the transfusion requirements of sick infants more accurately, with the aim of normalizing RCV and BV--securing euvolaemia--at the end of the transfusion. This may allow a complete correction of the RCV deficiency at the first occasion of transfusion. This approach may reduce donor exposures and also optimize oxygen transport and organ perfusion of the infant undergoing intensive management, perhaps leading ultimately to improved survival rates and fewer long-term complications of neonatal intensive care.

First clinical implications of perioperative red cell volume measurement with a nonradioactive marker (sodium fluorescein).

We measured red cell volume (RCV) with the nonradioactive marker sodium fluorescein (SoF) in 30 patients undergoing gynecological operations. Sixteen patients underwent preoperative isovolemic hemodilution (PIHD). RCV measurements were performed before and after PIHD and at the end of the operation. All RCVs were related to corresponding hematocrit (hct) levels. We report a simplified method for its clinical application by reducing the number of blood samples required. To validate our method, we compared RCV within the PIHD bags (bag RCV) with the difference of the patients' RCV before and after PIHD. Bag RCV obtained during PIHD (mean 399+/-81 mL) was measured with a precision of 4.2% by using SoF. There was a significant difference (mean 286+/-401 mL; P < 0.05) between intraoperatively estimated and measured blood loss. The blood loss tended to be underestimated and, in some cases, was underestimated or overestimated substantially. Preoperative and postoperative hct values only offered an imprecise estimation of the patients' RCV. We conclude that RCV measurement using SoF is a precise method for monitoring changes in RCV during PIHD and surgical operation. We measured red cell volume changes of 30 patients with the nonradioactive marker sodium fluorescein before and after hemodilution and postoperatively with a high precision. We frequently found large differences between intraoperatively estimated and measured blood loss. Preoperative hematocrit values offered an imprecise estimation of the patients' red cell volume.

First Clinical Implications of Perioperative Red Cell Volume Measurement with a Nonradioactive Marker (Sodium Fluorescein)

We measured red cell volume (RCV) with the nonradioactive marker sodium fluorescein (SoF) in 30 patients undergoing gynecological operations.Sixteen patients underwent preoperative isovolemic hemodilution (PIHD). RCV measurements were performed before and after PIHD and at the end of the operation. All RCVs were related to corresponding hematocrit (hct) levels. We report a simplified method for its clinical application by reducing the number of blood samples required. To validate our method, we compared RCV within the PIHD bags (bag RCV) with the difference of the patients' RCV before and after PIHD. Bag RCV obtained during PIHD (mean 399 +/- 81 mL) was measured with a precision of 4.2% by using SoF. There was a significant difference (mean 286 +/- 401 mL; P < 0.05) between intraoperatively estimated and measured blood loss. The blood loss tended to be underestimated and, in some cases, was underestimated or overestimated substantially. Preoperative and postoperative hct values only offered an imprecise estimation of the patients' RCV. We conclude that RCV measurement using SoF is a precise method for monitoring changes in RCV during PIHD and surgical operation. Implications: We measured red cell volume changes of 30 patients with the nonradioactive marker sodium fluorescein before and after hemodilution and postoperatively with a high precision. We frequently found large differences between intraoperatively estimated and measured blood loss. Preoperative hematocrit values offered an imprecise estimation of the patients' red cell volume. (Anesth Analg 1998;87:1234-8)

High predictive value of red cell volume measurement using carboxy-haemoglobin in a rabbit model of haemorrhage

We have studied the accuracy of blood volume measurements using carbon monoxide (CO)-labelled haemoglobin (COHb) injection and dilution (CO method) by comparing changes in red cell volume (RCV) measured using the CO method and 51Cr-labelled erythrocyte dilution (51Cr method) in a haemorrhage and infusion model in rabbits. RCV was measured repeatedly using the CO method at four different blood volume stages (stages I-IV). At stages I and IV, RCV was measured simultaneously using the 51Cr method. In comparing the sum of the circulating RCV and extracted RCV (SUM RCV) using the CO method, the values were almost equal and there were no significant differences between the values at the four stages. In comparing circulating RCV measured using the CO method and the 51Cr method, mean difference between the two methods was 0.80 (SD 0.76) ml kg-1 or 4.7 (4.6)%, and a positive correlation was observed (r = 0.91). We conclude that the CO method can be used to measure blood volume during perioperative periods in infants because it avoids use of a radioactive tracer, is simple and repeated measurements are possible.

Red Cell Volume Determination Using a Stable Isotope of Chromium

To validate and improve a method of red cell volume determination by use of a stable isotope of chromium. Twelve subjects were sequentially injected with red blood cells labeled with a stable isotope of chromium (53Cr) and red blood cells labeled with radioisotopic chromium (51Cr). Measurement of 53Cr dilution was by gas chromatography/mass spectrometry. Measurement of 51Cr dilution was by gamma counter. Comparison of the two methods led to results that differed on average by 34.5 +/- 45.0 mL (1.8 +/- 2.2%), 0.3 to 3.2%, 95% confidence interval. Measurement of red cell volume by use of a stable isotope of chromium is accurate, with potential applications including measurement in pregnant women and children or other groups in whom exposure to radioisotopes is undesirable.

Description of an instrument for separation of red cells from plasma and measurement of red cell volume

Description of an instrument for separation of red cells from plasma and measurement of red cell volume

Liver giant mitochondria revisited.

To examine the correlation between the severity of alcohol induced liver damage and the presence of intracytoplasmic red bodies (defined as periodic acid-Schiff diastase negative, globular, hyaline cytoplasmic inclusions larger in size than the hepatocyte nucleolus). To investigate the incidence of intracytoplasmic red bodies (ICRBs) in non-alcoholic liver disease. Liver biopsy specimens from 53 patients with alcoholic liver disease and 50 patients with a variety of nonalcohol related liver diseases were examined by light microscopy for the presence of ICRBs. For the 53 patients with alcoholic liver disease an assessment of recent alcohol consumption was made indirectly from measurements of red cell volume (MCV) and plasma gamma-glutamyl transferase (GGT). In addition, 10 liver biopsies with alcohol induced changes and ICRBs were examined by electron microscopy for the presence of mitochondrial aberrations including enlargement. ICRBs were detected in 18 of the 53 liver biopsy specimens showing alcohol induced changes, and were more abundant in those showing more advanced changes. Those patients whose liver specimens contained ICRBs were found to have a significantly higher mean plasma GGT activity and mean MCV than those individuals whose liver biopsy specimens did not contain ICRBs. Two of the 50 liver biopsy specimens showing non-alcohol induced changes contained ICRBs. Giant mitochondria were not detected by electron microscopy, but this may reflect sampling. The results of this study indicate that ICRBs are definitely associated with alcoholic liver disease and are more likely to be found in liver biopsy specimens showing more advanced alcohol induced damage, and when recent alcohol consumption has been high.

7 Flow cytometry: clinical applications in haematology

The time interval between the development of a new technique or methodology and its acceptance, if successful, as a recognized clinical application can be many years. The application of flow cytometry to reticulocyte counting, for example, has taken 8 years from the appearance of the first publication, and in 1990 it is still in its infancy as a clinical method. It is therefore a challenging task to anticipate which of the methodologies currently under development will achieve acceptance. It would be impossible to deal with all the candidates in the space available, and so a review is provided to those methods that may have potential applications in clinical haematology, together with some of the more practical details of methods that have recently been demonstrated to be viable in the clinical laboratory. The first category consists of leukocyte enumeration and studies on bone marrow, neutrophils, platelets and cellular DNA content, whilst the second covers reticulocyte counting and total red cell volume measurement. The contribution of flow cytometry to the field of immunophenotyping haematological disorders is probably unique in already being clinically acceptable. Finally, the question of quality control is addressed, as this is an essential prerequisite to the adoption of any new method in the clinical laboratory.