H yperglycem ic M acrocytosis in Electronically D eterm ined M ean Corpuscular Volume

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1 ANNALS OF CLINICAL AND LABORATORY SCIENCE, Vol. 15, No. 4 Copyright 1985, Institute for Clinical Science, Inc. H yperglycem ic M acrocytosis in Electronically D eterm ined M ean Corpuscular Volume Use of Three D ifferent Automatic Cell Counters*! ANTONIO T. PLANAS, M.D.t, G. ARTHUR VAN VOOLEN, M.D., and LARRY A. KELLY, $ BS, SH(ASCP) $Department of Pathology and Department of Medicine, Veterans Administration Medical Center and S.U.N.Y., Upstate Medical Center, Syracuse, NY ABSTRACT Spurious macrocytosis in electronic cell counters has been associated with hyperglycemia. The increased mean corpuscular volume (MCV) is thought to be secondary to osmotic disequilibrium betw een the erythrocyte and the diluent used in the automatic cell counters. Employing three different hematology cell counters, the effects of increasing concentration of glucose (400 mg per dl to 2000 mg per dl), at different tem peratures and after various incubation periods w ere studied. In addition to m acrocytosis being tem p eratu re and glucose concentration dependent, the magnitude of cell size variation also depends on the type of instrum ent used. Introduction The observation that elevated levels of blood glucose can p ro d u ce spurious macrocytosis and low mean corpuscular hemoglobin concentration (MCHC) has attracted the interest of many investiga- tors2 3,4'5, ' 12 and medical societies. 8 T hese w orkers, after ru lin g out o th er causes of high m ean corpuscular volume (MCV) in the C oulter counter system, such as cold agglutinin and high leuko- * A preliminary report of this study was presented at the 26th Annual M eeting of the American Society of Hematology, Miami Beach, FL, Decem ber, 1984, and appeared in abstract form in Blood 64(5):29a (suppl.), t Address reprint requests to Antonio T. Planas, M.D., 800 Irving Avenue, Syracuse, NY cyte count, found th at th e only factor responsible for this elevated MCV was hyperglycem ia. This hyperglycem ic matrix effect has been corroborated by many authors in vitro and is believed not to occur in vivo.9 D uring an investigation of this phenom enon, perform ed on diabetic patients with a glucose level 5 2,3 0 0 mg per dl, 12 some corroborative in vitro experim ents using th ree different automatic cell counters w ere carried out. Two of these instrum ents, the C oulter SSr* and th e O rth o E L T - 8 f, em ploy com pletely different principles to m easure the MCV and to count the cells; the third * Coulter Electronics, Inc., Hialeah, FL t Ortho Diagnostic Systems, Inc., W estwood, MA /85/ $00.90 Institute for Clinical Science, Inc.

2 is a recently introduced cell counter in the American m arket, the Sysmex CC $ Most of the reports on this topic are based on the use of C oulter counters; one report11 briefly m entioned O rtho s ELT-8. The present study is the first one comparing the new Sysmex CC-800, the C oulter SSr and the E L T - 8 and offers several possible explanations for the variation noted in the results obtained with these instrum ents. Materials and Methods HYPERGLYCEMIC MACROCYTOSIS IN MCV 287 Blood draw n in ED TA v acu tain er tubes from apparently healthy adults was teste d. G lucose 1 in pow d er form was added to th e w hole blood in various am ounts to attain the following concentrations: 400, 800, 1200, 1600, and 2000 mg per dl. Before adding the powdered glucose, the aliquots of blood w ere incubated at 4 C, 25 C, and 37 C for 10 minutes. As soon as the glucose was added, the tubes were inverted 10 times. These specim ens w ere ru n in th e follow ing autom atic cell counters: C o u lter SSr, ELT-8 and Sysmex CC-800. Spun microhem atocrit (micro Hct), done by standard technique utilizing a Clay Adams m icrohem atocrit centrifuge, was d e te r m ined im m ediately after glucose was added and after 60 m inutes incubation. On one occasion the incubation tim e was extended to 75 min and 120 min at 4 C. A tim e study with the Coulter SSr was perform ed at 0, 5, 10, 20, and 60 m inutes after glucose was added, a t a glucose level of 2000 m g p e r dl. T em perature studies were carried out at 4 C, 25 C, and 37 C for all glucose concentrations, after 15 m inutes of incubation, using all three cell counters. One final experim ent consisted of the incubation of two ml of blood (with glucose concentration of Í TOA M edical E lectronics USA, Carson, CA Vacutainer Systems, Rutherford, NJ Sigma Chemical C o., St. Louis, MO Glucose, mg/dl F i g u r e 1. Effect of various blood glucose concentrations at 37 C on mean corpuscular volume (MCV) by different cell counters, as com pared to MCV derived from spun microhematocrit. mg/dl) with 2 ml of H em atall diluent!! for 15 m in u tes, and d e te rm in a tio n of the MCV using the C oulter SSr. Results Glucose added to whole blood from two apparently norm al, asym ptom atic, control individuals up to mg per dl (in 400 mg per dl increments) produced consistent elevation of MCV and hem atocrit (Hct) at 25 C and 37 C, and concom itant d e p ressio n of M C H C. The m ean corpuscular hem oglobin (M CH), w hich is H c t-in d e p e n d e n t, rem ain ed u n a lte re d. T hese ab n o rm alities in the indices w ere consisten tly seen in all three instrum ents (figures 1 and 2). The ELT-8, how ever, showed the sm allest in crease (about 10 p e rcen t). In te re s t ingly, the E L T - 8 show ed MCV values U Fisher Scientific Co., Fair Lawn, NJ

3 288 PLANAS, VAN VOOLEN, AND KELLY MCV fl »» 9 /, 95 / / / 90 I 85 - S '* Coulter Ssr Glucose: m g/dl 37 C 25 C 80 - C Minutes F i g u r e 3. Effect on mean corpuscular volume of temperature and time of incubation in high glucose medium, as measured by the Coulter SSr. G lu c o s e, m g /d l F i g u r e 2. Effect of various blood glucose concentrations at 25 C on mean corpuscular volume (MCV) by different cell counters, as com pared to MCV derived from spun microhematocrit. out of the normal range (80 to 96 fl) only at relatively high glucose concentrations (1200 mg per dl and up). The Sysmex CC-800 exhibited the largest increm ent in MCV, from a basal 8 8 fl (with no sugar added) to a maximum of 125 fl (42 percent increase) with a sugar concentration of 2000 mg per dl at 37 C. The Coulter SSr showed an interm ediate rise in MCV of 20 percent at 37 C (figure 1). Tim e study w ith th e C o u lter SSr revealed that at 25 C the MCV reached 55 percent of the maximum raise in five m inutes and 82 percent in 1 0 minutes. At 20 m inutes, it virtually reached the maximum increase (figure 3). W hen the te m p e ra tu re was 37 C, th e rate of increase was faster, rising 82 percent in five m inutes and reaching the maximum in 1 0 m inutes. The th ird experim ent dem onstrated the influence of tem perature on the variation of the param eters considered. At 4 C th e re was no a p p a re n t difference either in the MCV or in Hct. At 25 C th e re was a n o ticeab le change in the MCV, although less pronounced than at 37 C. Again, the smallest increase was seen with the ELT- 8 (4 percent at 25 C, 20 p e rc e n t at 37 C), and th e largest increm ent with the Sysmex CC-800 (19 percent at 25 C, 42 percent at 37 C) (figures 1 and 2). The H ct followed essentially the same changes described for the MCV at 25 C and 37 C (figure 4). The results of the calculated indices by means of spun m icrohct are depicted in table I. A predictable observation is that w hen th e m icroh ct was d e te rm in e d G lucose, m g /d l F i g u r e 4. Effect of 15 minutes incubation at various blood glucose concentrations on hematocrit, as measured by different cell counters, and compared to spun hematocrit.

4 HYPERGLYCEMIC MACROCYTOSIS IN MCV TABLE I E ffe c ts o f H yperglycem ia on E rythrocyte In d ices C alcu lated by Manual Hem atocrit T e m p e r a t u r e 4 C 2 5 C 3 7 C T im e I m m e d i a t e 6 0 ' I m m e d ia t e 6 0 ' I m m e d ia t e 6 0 f G l u c o s e a d d e d H c t MCV H c t MCV H c t MCV H c t MCV H c t MCV H c t MCV 0 a d d e d m g / d l m g / d l m g / d l m g / d l m g / d l immediately after the glucose was added, the H ct fell from approximately 46 p ercent to 40 percent (13 percent change) w ith little variation w ith different tem peratures. After 60 m inutes incubation, how ever, th e H ct had risen back to approxim ately the initial level prior to the addition of glucose, around 46 p e r cent at 25 C and 37 C. At 4 C there was no significant change after 60 m inutes incubation (on one occasion the incubation tim e was extended to 75 and 120 m inutes, w ith no change observed). W hen blood with glucose level of 2000 mg p er dl was incubated in equal pro portions with Hematall diluent for 15 m inutes, the MCV came down to 85 femtoliter (fl) from the original 101 fl. This determ ination was done w ith the Coulter SSr. Discussion Spuriously elevated MCV determ ined by electronic blood cell counters caused by hyperglycem ia has focused the attention of m any in th e recen t m edical literature ,1 2 This raised MCV seems to be secondary to an osmotic gradient betw een hypertonic erythrocytes and the relatively hypotonic, virtually aglycemic, diluent used by these automatic cell counters. 1, Most agree that the osm otic disequilibrium occurs during the initial stages of mixing the red cells w ith the diluent, since preincubation w ith th e d ilu e n t m akes th e sp u riously elevated MCV disappear This finding was corroborated by p rein cubating w ith d ilu e n t for 15 m in u tes. That this macrocytosis is an artifact owing to the diluent has been dem onstrated by H olt e t al5 by in cu b atin g h y p erto n ic (hyperglycem ic) erythrocytes w ith artificially-m ade hyperglycem ic diluent. In this way the glucose gradient betw een erythrocytes and diluent is eliminated, and no spurious m acrocytosis is observed. A nother well docum ented fact that this is an artifact is the absence of raised MCV when the spun Hct is used to calculate th e MCV. 2,5,6 7 9 By comparing the performances of two different m odels of autom atic cell counters, th e C o u lter S and the C o u lter S- Plus, H olt et al5 clearly dem onstrated th at th e d e g re e of m acrocytosis is greater with the C oulter S-Plus. This is due to the sample cycle characteristics of the instrum ents. W ater crosses the red cell m em brane instantaneously, tem porarily causing macrocytosis, whereas the T72 s for urea and glucose efflux are 7 to 10 seconds and 24 seconds, respectively. The shorter the tim e allowed for efflux before sizing takes place, the greater is th e d e g re e of sw elling d e te c te d. The Coulter S-Plus performs red cell sizing earlier in its cycle ( 1 2 to 2 1 seconds) than the C oulter S (33 to 39 seconds); th e re fore, there is less tim e for osmotic equilibration. 51 0

5 290 P L A N A S, VAN V O O L E N, A N D K ELLY The results of these experim ents are in general in a g re e m e n t w ith those reported in the recent literature, which shows that th e rise in MCV is proportional to th e co n c en tra tio n of glucose and is tim e and tem perature dependent. Time study revealed that the rise begins within five m inutes and virtually reaches th e m aximum point after 1 0 to 2 0 m inutes, depending on the tem perature (figure 3). Tem perature significantly influenced this p h en o m en o n, b ein g m ore m arked at 37 C. Almost no effect is noted at 4 C; all three instrum ents showed ± one fl variation in the MCV at 2000 mg per dl glucose concentration when the tem perature was kept at 4 C. W hen spun H ct was used for MCV calculation, no elevation of MCV was noted if the H ct was determ ined 60 m inutes after the glucose was added to the blood. If, how ever, the m icro H ct was d e te r m ined im m ediately after the glucose was added, the H ct declined an average of 5.6 p ercen t at all tem peratures tested (table I). The most likely explanation for this is that initially there was an efflux of water from the erythrocytes owing to relative in tra cellu la r hypotonicity. A fter som e tim e th e influx of glucose m olecules inside the cells equilibrated the osmotic gradient and the H ct returned to normal values and the MCV followed the same trend. This observation holds true at 25 C and 37 C. W ith low tem p erature (4 C) th ere is no appreciable change after 60 m inutes, and even after 75 and 120 m in u tes (data not shown). This is probably because low tem perature decreases all metabolic and osmotic activities, therefore not allowing osmotic equilibration. The E L T - 8 was th e instrum ent that showed the smallest change in MCV (figure 1) and Hct. Only at relatively high glucose concentrations did the MCV rise above the norm al range. The m ost plausible explanation of this is the technique the E L T - 8 em ploys for m easu rem en t TABLE I I Time Delay Before Counting A fter Second D ilu tion E L T -8 S S r C C s e c o n d s s e c o n d s 3. 5 s e c o n d s (laser technology), and the ELT-8 s very low dilution ratio (1:600), as com pared to the SSr and the Sysmex CC-800 (1:50000 and 1:25000, respectively). The ELT-8 s very low dilution ratio (1:600) appears to be the most im portant variable in its sizing of red cells since, as com pared to the SSr, its tim e delay before sizing is shorter (table II) and its diluent has almost the same osmolality. (The osmolality of the diluents are as follows: 340 mosm per Kg for the ELT-8 ; 338 mosm per Kg for the SSr; and 268 mosm per Kg for the CC- 800.) On the other end of the spectrum, the Sysmex CC-800 showed the largest variation in M CV and H ct (figure 1), which is in all probability secondary to the same factors m entioned previously. In th e SSr and th e C C -800, th e tim e delay before counting (table II) appears to play the leading role in equilibration, since b o th show a high d ilu tio n ratio. H ence, th e changes observ ed in the MCV seem to represent the result of a com plex in te rp la y of th ese factors, in addition to th e previously m entioned factors (time, tem p eratu re, glucose concentration). Clinically, spurious macrocytosis may be determ ined by noting that the M CHC is low and that the MCV and M CHC norm alize as th e serum glucose level decreases. Realizing this should keep the clinician from pursuing an unnecessary and costly w orkup for macrocytosis. In sum m ary, this study shows th at macrocytosis owing to hyperglycemia in electronically determ ined MCV is not only proportional to the concentration of glucose (up to mg p e r dl in our study), is tem perature and tim e dependent, and is essentially an in vitro and

6 H Y P E R G L Y C E M IC M A C R O C Y T O S IS IN M C V 291 transient phenom enon, b u t th e osmolality of the diluents, the ratio of dilution of the samples, and the tim e delay before counting also appear to play an im portant role. T he E L T - 8 show ed th e sm allest increase in MCV, whereas the Sysmex CC -800 show ed th e largest. It is concluded, therefore, that the m agnitude of the variation of the MCV is also in stru m ent-dependent. A d d en d u m : A fter subm ission of this m anuscript, TOA M edical E lectronics (USA), Inc., informed the authors that they im proved th eir diluent, and discontinued diluents C ellent and C ellent A, for use with their models CC-700, CC- 720 and CC-800 hem atology analyzer. Acknowledgm ents American Scientific Products provided the Sysmex CC-800 and reagents. The assistance of Greg W eisenberger, Technical Specialist, American Scientific Products is gratefully acknowledged. The invaluable cooperation of the Hematology laboratory staff cannot be overem phasized. Thanks are extended to Drs. G eorge C. H enegar and Stephen A. Landaw for reviewing this manuscript. References 1. A l l e n, S. C., B a l f o u r, I. C. and W i s e, C. C.: The red cell osmometer. A useful inaccuracy in m easurem ent of mean corpuscular volum e in hyperosm olar states. J. Clin. Pathol. 33:430, B e a u t y m a n, W. and B i l l s, T.: Osmotic error in erythrocyte volum e determ inations. Am. J. Hematol. 12:383, C o r n b l e e t, P. J., and M y r i c k, D.: Unusual RBC indices in diabetic patient. Lab. Med. 14:444, E v a n - W o n g, L. A., and D a v i d s o n, R. J.: Raised Coulter mean corpuscular volum e in diabetic ketoacidosis, and its underlying association with marked plasma hyperosmolaritv. J. Clin. Pathol. 36:334, H o l t, J. T., D e W a n d l e r, M. J., and A r v a n, D. A.: Spurious elevation of the electronically d eterm in ed m ean corpuscular volum e and hem atocrit caused by hyperglycem ia. A m. J. Clin. Pathol. 77:561, M o r s e, E. E., K a l a c h e, G., G e r m i n o, W., and S t o c k w e l l, R.: Increased electronic mean corpuscular volume induced by marked hyperglycemia. Ann. Clin. Lab. Sci. 11:184, O k u n o, T., G o l d f a r b, D., and O k u n o, S. H.: Electronically determined mean corpuscular volume and marked hyperglycemia. Am. J. Clin. Pathol. 78:571, S a v a g e, R. A. E vidence for hyperglycem ia osm otic matrix effects on the Com prehensive H em atology Survey Am. J. Clin. Pathol. 80(Suppl):626, S a v a g e, R. A.: H yperglycem ic osm otic matrix effect. Check Sample, American Society of Clinical P athologists, H em atology N o. H (H131). 10. S a v a g e, R. A. and H o f f m a n, G. C.: Clinical significance of osmotic matrix errors in automated hematology: The frequency of hyperglycem ic osmotic matrix errors producing spurious macrocytosis. Am. J. Clin. Pathol. 80:861, S t r a u c h e n, J. A., A l s t o n, W., A n d e r s o n, J., G u s t a f s o n, Z., and F a j a r d o, L. F. : Inaccuracy in autom ated m easurem ent of hem atocrit and corpuscular indices in the presence o f severe hyperglycemia. Blood 57:1065, V a n V o o l e n, G. A., K e l l y, L. A., P l a n a s, A. T., and O a t e s, R. P.: Relationship of blood sugar to MCV. Blood 62:28a, abstract 15, 1983.