METHOD FOR SPHERING AND FIXING WHOLE BLOOD ERYTHROCYTES

Abstract: A one-step method (and sphering agent/fixing agent useful therein) for treating mammalian red blood cells in a sample which can be effectively measured electrooptically for determination of red blood cell volumes, which compris­ es treating an anticoagulated whole blood sample with a single aqueous sphering agent/fixing agent reagent at a temperature in the range of 4°C to 37°C over a reaction period of up to 180 seconds employing a whole blood dilution factor of from 1:300 to 1:4,000, wherein said one-step, single reagent treatment provides isovolumetric sphering of the erythrocytes in the sample independent of the concentration of said erythrocytes in the whole blood sample and without inducing lysis of said erythrocytes in the resulting diluted sample. The preferred sphering agent is an alkali metal salt of an alkyl sulfate in an amount 0.5 to 3.0 mg %, and the preferred fixing agent is an aldehyde in an amount from 0.05 to 0.3%.

Description: This invention relates generally to a rapid one-reagent method for sample preparation for improved electrooptical methods for measuring human and animal erythrocyte volumes and cell hemoglobin contents. More particularly, it relates to a one step method for treating mammalian red blood cells in a sample so that they can be effectively measured electrooptically for their volumes whereby the one-step, single reagent treatment provides isovolumetric sphering of erythrocytes in the sample independent of erythrocyte concentration in the original blood sample and without inducing lysis. Prior art methods utilizing the measured amount of light scattered from individual red cells (erythrocytes) to determine the individual and mean volumes of red cells are subject to error for two reasons: since the native human red cell is a biconcave disc, the amount of light scattered will vary with the orientation of the cell with respect to the incident light beam; and the shape of the cells can change during dilution and pumping steps. For a discussion of this, see Hemolysis and Related Phenomena, Chapter II pp 10-49 by Eric Ponder (1948) and Transformation and Restoration of Biconcave Shape of Human Erythrocytes Induced by Amphilic Agents and Changes of Ionic Environment, Biochemica et Biophy. Acta, Bernard Deuticke, pp 494-500 (1968). In Ornstein et al U.S. 4,412,004, a method is described which substantially eliminates both of the above-described causes of error and provides an improved method for determination of human red blood cell volumes. In the above U.S. patent, the method involves a two-step procedure of first sphering erythrocytes isovolumetrically and then fixing isotonically. The method was devised as a two-step procedure in order to ensure that sphering had reached completion before the fixing process began, since otherwise cells might become "stiffened" by cross-linking which occurs during fixation and thus become "frozen" in some shape intermediate between the native biconcave shape and the desired spherical shape. Fixing immediately after sphering permitted the use of higher sphering agent/protein ratios in the fixing solution because cells which might otherwise lyse were fixed before that could happen. This led to a more convenient implementation for automated clinical use. It has now been found, quite unexpectedly, that a single reagent containing appropriate and limited ranges of concentrations of both sphering agent and fixing agent can achieve complete isovolumetric sphering of all erythrocytes of a large range of clinical samples of blood, independently of the concentration of erythrocytes in the whole blood sample, and without inducing lysis of any of the erythrocytes in any of the diluted blood samples. It is surprising that the employment of particular parameters in a one-step method can result in a procedure in which the speed of the sphering step remains sufficiently greater that the fixing process so that the cells are substantially completely sphered before they have appreciably stiffened. This leads to a faster and still more convenient implementation for automated clinical use. In accordance with one aspect of this invention, we have devised a one-step diagnostic method for treating mammalian red blood cells in a sample which can be effectively measured electrooptically for determination of red blood cell volumes, which comprises treating an anticoagulated whole blood sample with a single aqueous sphering agent/fixing agent reagent at a temperature in the range of 4 o C to 37 o C over a reaction period of up to 180 seconds employing a whole blood dilution factor of from 1:300 to 1:4,000, wherein said one-step, single reagent treatment provides isovolumetric sphering of the erythrocytes in the sample independent of the concentration of said erythrocytes in the whole blood sample and without inducing lysis of said erythrocytes in the resulting diluted sample. Preferably, the concentration of sphering agent in the reagent is from about 0.5 mg % to about 3.0 mg %, most preferably not more than 2.0 mg %. The most preferred concentration is about 1 mg %. (As used herein, 1 mg % means 1 mg per 100 ml of solution.) Preferably, the sphering agent is an alkali metal salt of an alkyl sulfate, e.g. sodium dodecyl sulfate. It is to be understood, however, that any suitable sphering agent can be used. Preferably, the fixing agent, e.g. glutaraldehyde, is provided at a concentration of from about 0.05% to about 0.3%, preferably at about 0.2%. For the purposes of this invention glutaraldehyde is preferred; however, other aldehydes, such as formaldehyde and other fixing agents known in this technology can be employed. Advantageously, a phosphate buffer can be included in the aqueous reagent, preferably at a concentration adjusted to provide a reagent pH of from 6.0 to 7.5, and more preferably at a concentration of about 0.035 M to provide a reagent pH of about 7.3. Sodium chloride can be added to the aqueous reagent, preferably at a concentration adjusted to provide a reagent osmolarity to about 290 mOs/kg. The method of the invention is most preferably effected at about 25 o C over a period of about 60 seconds and at a whole blood dilution factor in the range 1:600 to 1:700. In accordance with another aspect of this invention, there is provided a composition use in the above method, for sphering red blood cells in an anticoagulated whole blood sample in a single step to provide isovolumetric sphering independent of the red blood cell concentration in the whole blood sample and without lysis inducement, which comprises an aqueous sphering agent/fixing agent reagent comprising from about 0.5 mg % to about 3.0 mg % of a sphering agent and from about 0.05% to about 0.3% of a fixing agent, and a phosphate buffer to provide a reagent pH of 6.0 to 7.5. It will be understood that the preferred features enumerated above with respect to the method also apply with respect to the composition of the invention. The one-step method of the invention is a significant improvement over prior art methods especially with regard to its kinetics and its ability to be adapted to an automated system. It allows for the production of single formulations of reagents which substantially completely and isovolumetrically sphere all erythrocytes of a large range of clinical samples of blood, independently of the concentration of erythrocytes in the blood samples, and without inducing lysis of any of the erythrocytes in any of the diluted blood samples. In the method of the invention, the reaction conditions, e.g. the concentrations and temperatures, are such that the particular desired reaction kinetics are obtained, i.e. the rate of sphering remaining sufficiently greater than the rate of fixing so that the cells are completely sphered before they have stiffened appreciably. One preferred set of conditions is given, merely by way of example, below: Temperature: room temperature (25 o C ± 8 o C) Whole blood dilution factor: 600 ± 100 Reaction time: 60 seconds ± 40 seconds Reagent formulation: sodium dodecyl sulfate: 1 mg % ± 0.2 mg % glutaraldehyde: 0.2% ± 0.1% phosphate buffer: 0.035 ± 0.015 M at pH 7.3 ± 0.2 sodium chloride: to adjust reagent osmolarity to 290 ± 5 mOs/kg When a whole blood sample is mixed with the above reagent, red cells are isovolumetrically sphered for more accurate and precise cell volume and hemoglobin measurements by a light scattering flow cytometer. A preferred flow cytometer for the measurement uses a HeNe red laser (wavelength 632.8 nm) as the light source, and the illuminated field is defined as a 20 µm x 100 µm slit imaged in the center of the sheathed flow cell. Two optical light scatter measurements are taken, the low (2 o to 3 o ) angle signals and high (5 o to 15 o ) angle signals. The low angle signals and the high angle signals are paired to form a 50 x 50 erythrocyte volume and hemoglobin cytogram (the other high angle signals can be used to generate the platelet histogram). The cytogram's data are processed by coincidence trimming followed by a non-linear two-dimensional transformation. A computer program transforms the scatter amplitude signals into erythrocyte volume and hemoglobin concentration histograms. The following parameters can be generated from the cell preparation: 1. Red blood cell count (RBC) 2. Man corpuscular volume (MCV) 3. Cell hemoglobin concentration mean (CHCM) 4. Hematocrit (HCT) 5. Red cell volume distribution width (RDW) 6. Hemoglobin distribution width (HDW) 7. Platelets (PBC) 8. Mean platelet volume (MPV) 9. Plateletcrit (PCT) 10. Platelet distribution width (PDW) Broader parameters applicable to the present invention are provided hereinbelow: Reaction Temperatures: can be varied from 4 o C to 37 o C without risking any significant change in results. +.37% at 4 o C and -0.62% at 37 o C in whole blood MCV were observed. No change occurred in RBC and Plt counts at either temperature. Whole Blood Dilution Factor: can be varied from 1:300 to 1:4,000 without risking any significant change in results. Less than +1% at 1:300 and less than -1% at 1:4,000 in fresh whole blood MCV has been observed. Sphering Agent Concentration: can be varied from 0.5 mg % to 3.0 mg % when all test samples are fresh whole blood. Aged blood samples are more prone to lysis at concentrations above 2.0 mg %. Fixing Agent Concentrations: can be reduced to 0.05%. Above 0.3%, there is interference with uniform sphering and excessive cross-linking takes place before sphering of erythrocytes is complete. pH of the Reagent: can range from 6.0 to 7.5. One pH unit beyond these limits produces -1.5% change in MCV and +1.5% in CHCM to whole blood. Reaction Times: at 180 seconds, there is less than 1% change in whole blood MCV and CHCM. Times of up to 300 seconds result in MCV's with less than -2% error and CHCM's with less than +2% error. In order that the invention may be more fully understood, the following Example is given by way of illustration only. EXAMPLE Instrument 1) Light Source: HeNe red laser (λ = 632.8 nm) 2) Illumination Field: 20 µm x 100 µm slit 3) Sheathed Flow cell (Sheath fluid = phosphate buffered saline, 290 mOSm/L, pH 7.4) 4) Two Optical Light Scatter Measurements Angle: Low 2 o to 3 o High 5 o to 15 o 5) Sample Stream Width: 15µ Procedure 1) 0.01 ml whole blood (EDTA anti-coagulated) sample was added to 6.0 ml of the reagent and mixed immediately. The red cells are isovolumetrically sphered. 2) The sample of sphered and fixed red cells is aspirated through a sample stream and a 40 second reading is taken. The low angle signals and the high angle signals at low gain are paired to form a 50 x 50 RBC cytogram. The other high angle signals (x10 low gain) are used to generate the platelet histogram. The cytogram's data are processed by coincidence trimming followed by a non-linear two dimensional transformation. A computer program transforms the scatter amplitude signals into RBC volume and a hemoglobin concentration histogram. The system must be precalibrated, e.g. by using 10 normal bloods whose parameters are pre-determined by reference methods.

Claims: A one-step diagnostic method for treating mammalian red blood cells in a sample which can be effectively measured electrooptically for determination of red blood cell volumes, which comprises treating an anticoagulated whole blood sample with a single aqueous sphering agent/fixing agent reagent at a temperature in the range of 4 o C to 37 o C over a reaction period of up to 180 seconds employing a whole blood dilution factor of from 1:300 to 1:4,000, wherein said one-step, single reagent treatment provides isovolumetric sphering of the erythrocytes in the sample independent of the concentration of said erythrocytes in the whole blood sample and without inducing lysis of said erythrocytes in the resulting diluted sample. A method according to claim 1, wherein the concentration of said sphering agent in the reagent is from 0.5 mg % to 3.0 mg %. A method according to claim 1 or 2, wherein said sphering agent is an alkali metal salt of an alkyl sulfate, for example sodium dodecyl sulfate. A method according to any of claims 1 to 3, wherein the concentration of said fixing agent is from 0. 05% to 0.3%. A method according to any of claims 1 to 4, wherein said fixing agent is glutaraldehyde. A method according to any of claims 1 to 5, wherein said aqueous reagent includes a phosphate buffer to provide a reagent pH of from 6.0 to 7.5. A method according to any of claims 1 to 6, wherein said aqueous reagent includes sodium chloride, preferably in an amount to provide a reagent osmolarity of up to about 290 Os/kg. A method according to any of claims 1 to 7, wherein the resulting, diluted sample is subjected to light scattering measurement. A composition for use in the method of claim 1, for sphering red blood cells in an anticoagulated whole blood sample in a single step to provide isovolumetric sphering independent of the red blood cell concentration in the whole blood sample and without lysis inducement which comprises an aqueous sphering agent/fixing agent reagent comprising from 0.5 mg % to 3.0 mg % of a sphering agent and from 0. 05% to 0.3% of a fixing agent, and a phosphate buffer to provide a reagent pH of from 6.0 to 7.5 A composition according to claim 9, which has the features of any of claims 3 to 7.

Inventors: KIM, YOUNG RAN, ORNSTEIN, LEONARD
Applicants: TECHNICON INSTRUMENTS CORPORATION(A DELAWARE CORPORATION)
Application year: 1985
Main classification: G01N33
IPC codes: G01N33