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C LIN IC AL C HEM IST RY , V ol. 35, N o. 9, 1989 2017

Fig. 1. (top) High-resolution elect rophores ison agar os e ge l w it h be ta -m ig ra tin g r es tr ic -tio n o f fib rin og en in 1 gMwe ll, a nd (bottom)immunofix at io n o f p la sma , s how ing c ro ss -reac ti vi ty o f an ti -I gM reagen tw i th f ibnnogen

tio n d oe s n ot c le arly identify (2). Anisolated li gh t- ch a in r es tr ic tio n shou ldbe corroborated b y u rin e immunoelec-tro ph ore sis , a nd a n is ola te d h ea vy-ch ain re stric tio n sh ou ld b e co nfirm edby immu no se le ctiv e s er um e le ctr op ho -resis (Ouchterlony m ethod). If follow -u p s tu die s do no t support th e immu-n oflxa tio n results, m in or cro ss-rea c-tivities of the antisera shou ld besuspected. The location of the band onhigh-reso lu tion e lectrophores is cang uide scree nin g fo r co nta min atin g a n-tibod ies on monospecific serum .A nti-fib rin og en a ntib od ie s in p articu -la r shou ld be considered b ec au se o f th eh aza rd o f m isid entificatio n of a fib rin -ogen band as a beta-m igra ting m ono-c lona l ga inn iopa thy .References1. K er en DF . H ig h r es olu tio n e le ctro ph o-resis and immunof ixat ion. Boston:Butter-wor th Pub li she rs , 1987.2 . K ere n DF, Warren J, Lowe J. Strategyto d iagnose monoc lona l gammopathy inserum. Cl in Chem 1988 ;34 :2196 -201 .

Dept . o f P a tho l.Loretta J. Register

D avid F. K erenB io ch em . S ec tio n an dClin. Immunopathol.Univ. of M ic hig an H os pita lsAnn Arbor, M I 4 810 9

idated their Z index. They provide nodata o n th e co nfid en ce limits for theslopes used in the ir index, nor havethey shown it to be valid in extremes ofalbumin c on ce ntr atio n b y d emons tra t-ing that it correlates c orr ec tly w ith th ep atie nts c lin ic al condi t ions.The fact that the FF1 fa ils to correctfor extrem e abnorm alities of bind ingp ro te in s sh ou ld no t present a p ro blem :the very low or very h igh T3U valuesth at re su lt in su ch ca se s s ho uld a le rt th eclinica l chem ist so that add itiona l spe-cia liz ed in ve stig atio ns ca n th en b e d on e.L indstedt et a l. (2 ) have drawn at-tention to the need for statistica l ana l-ys is to be an ad junct to , rather thanre pla ce , so un d p ath op hy sio lo gica l co n-s idera tions. These considerationse qu ally a pp ly to the in terpre ta tion ofT3U measurements .References1 . B eck R , Mas sa d A , L is ch in sk y S . Effect ofalbumin on results fo r th e free-thyroxin in -d ex a s est imated by the tota l T JF , u ptaker atio [L e tt er ]. C li n Chem 1989 ;35 :7 06- 7.2 . Lindstedt G , N ystro m E , L un db erg P A.Statistics, common s en se , a n d s er um fr eeT4 in d isease [Letter]. C lin Chem1987;33:1293-4.

Dept. of Chem . Pat/w i.Northern G en eral H osp .Herries Rd .Sheffield S5 7A U, UJC.

A. PriceH. Gr i ff ith s

si s w as thus suspected to be f ibrin-ogen. To determ ine that the lot ofanti-IgM in use (goat anti-hum an 1gMIE P an tis e ra ; Ka lle s tad Diagnost ics)contained ant ibodies to both 1gM andfibrinogen, w e perform ed immunof ix-ation on a normal p lasma sample. Asshown in Figure 1 (bottom), th is gave afalse precipitin b an d a t th e s am e p oin to f m ig ra tio n a s f ib rin og en .Fibrinogen is a normal band ob-served on high-resolution elect ropho-res is o f p lasma but not of serum , sodetection of fib rinogen w arrants care-fu l review of possible causes for itsp re se nce . In th e p re se nt ca se , t he sp ec-im en subm itted was actua lly plasm abut had not been so identified . Chartrev iew revealed that the patient, a35-year-old gravida 8 para 1 w om an,was rece iv ing heparm n adjunctive tohemodia lysis for pestpartem rena lfailure . H eparin adm in istered in vivofunctionally converts serum toplasma.Immunofixa tion shou ld be per-form ed w henever a beta-m igra tingm onoclona l restriction is suspectedth at seru m im mu no glo bu lin qu an tita -

Author fo r correspondence.

More on A lb um in a nd ThyroidHormonesT o th e E ditor:

We have several comments on the Zindex proposed by Beck et a l. (1). Thepatient population they chose containscritically ill patients and patients inth e immediate p ostop era tive p eriod .In our experience a h ig h p ro po rtio n o fth es e p atie nts w ill h av e lo w albuminco nce ntra tion s, o win g to th eir nutri-tio na l s ta te , and low T4 concentra-tions, owing t o th e s ic k e ut hy ro id syn-d rom e. T his emp ha siz es th e s ta tis tic almax im : C orre la tio n is n ot ca usa tio n.Because a lbum in is a thyro id-hor-mone-binding protein , w e do not find itsurprising that the T3 uptake ratio(T3U) dec reases w i th i nc reasi ng a lbu -m in c on ce ntra tio n. F urth erm ore , th eincreased free fatty acids found ins om e c ritic ally ill p atie nts a re knownto invalidate the T3U in these cases.Beck e t a l. (1 ) have i ncomple te ly va l-

Aqueous-Based G lucose ControlSolut ions fo r Use w it h G lu co seR ea gen t-S trip s a nd M eter sT o th e E ditor:The use of ref lectance photometersto rap idly a sse ss blood g lucose concen -t ra tio ns h as b ec ome a ma jo r adjunct toth e care of in div id ua ls w ith d ia be te sm e llitu s. D if fe re nc es in r ea ge nt- str ipc he mis try u se d b y v ario us m an ufa c-t ur er s, h owe ve r, h av e crea te d a m ajo rproblem in the design of an external

q ua lity-con trol p rog ram b as ed o n us eo f a s in gle a qu eo us g lu co se s ta nd ard .In a recent comparison o f b lo od g lu-cose mete rs , Brooks et a l. (1,2) high-lighted anom alous results obtainedw ith b oth a qu eo us - a nd s eru m-b as edc on tro l m ate ria ls . W h en w e e xamin edth is basic discrepancy in the use ofa qu eo us -b as ed c on tro l m ate ria l, it b e-came o bv io us th at s olu tio n v is co sityw as the m ajor factor affecting the re-a ct iv it ie s o f d if fe re nt r ea ge nt s tr ip s.The m ajor d ifficu lty in using a com -m on aqueous-based contro l for both

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T ab le 1 . E va lu atio n o f Aqueous-Based Glucose C on tro ls b y U se o f B MG20-800 an d Glucost ix Reagen t S t ri psGlucose,mmol/L n

So lu ti on /7715

1566

Found,mmol/L CV,%20202020

156c10 6666

8.39.415.616.17.07.318.516.611.111.06.56.3

1. 18.42.57.613.510.91. 03.72.45.75.95.0

9 65 188cDextro-Chek 192C

Actual concentrat ion prepared.b B ,BMG2 0-8 00 ; G , Gtucost ix.C Numberof ind iv idualsanalyz ingthesolution. d Purcha sedfrom MUesAust .Ply.Ltd. ;s tated range fo r t he so lu ti on I s 5 to 7 mmoVL.

Solution I I18189

Glucostix (Miles Labo ra to rie s Aus t.P ty. Ltd ., M ulgrave N orth , V ictoria)a nd BM -TEST -G LYCEM IE 20-800(B MG 2 0-8 00 ; Boehringer MannheimAust. P ty Ltd., N orth R yde, N.S.W.)r ea ge nt s tr ip s was in the re sp on se o fth e G lu co stix strip. Because of itsmembrane and paper-matrix padcomposition (3), t he G lu co st ix r ea ge ntstrip is part icularly s en sit iv e t o s olu -tion v is co sity , w h ic h w e soon foundhad to be particularly h ig h if res ultswere to be reasonable . The BMG 20-80 0 strips are fa r less s en sitiv e toviscosity.In early experiments in vo lv in g th eus e o f s olu tio ns o f p oly et hy le ne g ly co l6000 (PEG-6000), a c on ce ntra tio nran ge o f 1 50 -2 50 g/L w as fo un d nec-essary for a m ean in gful re sp on se. Be-low this range, g lucose values werefact it iously h ig h; a bo ve it, th e o pp os iteeffect was noted. M oreover, o ther im -p or ta nt fa cto rs in clu de d t he b uf fe rin gcapacity and pH of the f inal solution.G uided by our overa ll find ings, weprepared tw o solutions for m ore de-ta ile d e va lu atio n. S olu tio n I co nta in edPEG -6000 (150 g/L), so diu m p hytate(1 0 mmolJL), Na3PO4 12H20 (100mmol/L), Tween 20 surfactant (4 g/L),an d phenol (2 g /L); the pH wasadjusted to 6.5 w ith phosphoric acid .Solution H conta ined P EG -6000 (220g /L ), T we en -2 0 (7 g/L), and phenol(2 g/L) in C larke and Lubs buffer, pH6.0(4). A trace of neutra l-red indicatorw as a dd ed fo r c olo ra tio n, a nd th e s olu -t ions w ere a llo we d to equilibrate atroom temp era tu re fo r a t le as t tw o daysb efo re u se .Table 1 summar izes th e results fo rSolu tion s I and H. As indicated in pre-2018 CL IN ICAL CHEM ISTRY, Vo l. 3 5 , No . 9 , 1 989

v ious studies (1), and cons is ten t withth e results in T ab le 1 , g lu co se is m oreprecisely est imated by use of the B MG20-8 00 r ea ge nt strips than w ith G lu-c o sti x s tr ip s. Solution H is not totallysuitab le for the B MG 20-800 reagents tr ip , h owe ve r, b ec au se n o me te r r ea d-ing is obtained f or g lu cose concent ra -t io ns b elow 4 .5 mmol/L. The high C Vsfo r th e G lu co stix re ag ent strip withSolution I are a consequence of thes tr ic t adhe rence to procedural require-ments tha t are necessary if a n a cce pt-a ble v alu e is to b e o bta in ed . S ho rte r o rlo ng er in te rva ls b efo re th e s am ple is blo tte d o n th e r ea ge nt pad markedlyinfluence the final result. For thesela tte r re as on s, e stim ate s with SolutionII are markedly mo re p re cis e. Bothso lu t ions , s tored a t room temperature,g av e th e s ame meas ur ed g lu cose con-centration fo r at le as t tw o m on th s.Although both re ag en t s trip s h av ea n o bvio us p os itiv e b ia s at lo we r g lu -c os e c on ce nt ra tio ns , w e c on sid er t hisof secondary im po rta nc e c om p are dw ith p re cis io n, b ec au se the p rim e a p-p lic atio n o f c on tro l s olu tio ns is to as-sess the perform ance of the analystwith r espec t t o t he es tab lish ed char ac -te ris tic s o f th e solution b ein g u sed .M oreover, the concept of a truevalue is not strictly applicable tob lood -g lucose mete rs , because manu-facturers use algorithm s to convertth e re ag en t-s trip s ra te o f re ac tio n towho le b lood, capillary blood,or plasmag lucose equ iva len ts. Compar ison witha re sp ec tiv e la bo ra to ry g lu co se e sti-m ation m ay therefore be invalid un-le ss t he m anu fa ct ur er unequivocal lys ta te s t he ca lib ra ti on medium f or th eme te r/r eagen t s tr ip combina tion (5).

References1. Brooks KE, R aw al N , H enderson AR .Labo ra to ry a ss es smen t of three new mon i-tors of b lood g lucose : Accu -Chek H , G lu -StrIp cometer II, and G lucoscan 2000 .C lin Chem1986;32:2195-200.

Bb 2. R aw ai N , H en derson A R. Quality-con-tr ol ma te ria ls fo r use w ith m onitors of

B blood glucose: Ref lo f lux U (BoebringerMannheim) and Sugar-Chex (Streck Lab-G oratories) contro ls [Letter]. C lin C hemG 1987;33:1294-5.G 3. Walte r B . D ry reagen t c hem is tr ie s [R e -view]. Anal Chem 1983 ;55 :498A-514A.B McKenzie H A, Dawson RMC. pH andb uffe rs p hy sio lo gic al m ed ia . In : D aw so nG RMC, Elliot DC , E ll io t WH , Jones 1CM,eds.B Data for b iochem i ca l resea rch , 2nd ed.G Glasgow: Oxford University P ress,G 1969:490.,. 5. C ohen M . W hich r e fe rencemethod fo rcomp arin g b lo od g lu co se re ag en t strips[Letter]? Diabetes Care 1988;11:747-8.

Geo rg e Ph illip ouRobert K . FarrantPatr ic k J . P hillip sEndocrine and D iabetes Lab.T he Q ueen E liz ab eth H os pita lWooduille, South Australia 5011Australia

Es tima tio n o f B ra in L es ion S iz eB as ed o n Qua ntify in g CK -BB InSerumT o th e E ditor:

Schwartz et a l. (1), in describingtheir a ttem pt to use the quant if icat ionof serum creatine kinase (CK, EC2 .7 .3 .2 ) a c tiv it y, CK -BB isoenzyme ac-tivity, a nd th e ra tio o f th es e tw o d eter-minat ions as indices of the size ofbrain lesions from various causes,fo und n o co rre latio n between any ofth e fa cto rs s tu die d an d th e size o f th ebrain lesions. They attributed thislack of corre lat ion to an intact blood-brain barrier, th e rap id e lim in atio n o rinactivation of CK -B B, or a com bina-tion of these factors. They fai led toc on sid er th at th eir fin din gs c ou ld a ls obe expected if the distribution of CKand CK -BB was not homogeneousfrom region to re gio n th ro ug ho ut th ebrain.In a study of canine brain (2), were porte d a d efin ite reg io nal va ria tionin ac tiv it y concent ra ti ons of CK isoen-zymes, w ith C K-B B vary ing by m oreth an tw ofo ld from region to region.However, we could not identify anydefinitive pattern for grey vs whitematter. The only o th er C K isoenzymepresent in brain , m itochondria l CK ,also show ed a regional variation inactivity co nce ntra tio ns in tissue . l ithed is tr ib utio n p atte rn of CK isoenzymes