A. Clerico

C. Cipolloni

G.C. Zucchelli

M.G. Del Chicca

P. Biver

M. G. Del Chicca

G. C. Zucchelli

CLERICO, ALDO

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157150CLINICAL CHEMISTRY, Vol. 39, No. 4, 1993 695nosis of bacterial and viral infections. KlinWochenschr 1990;68:218-22.Mikhail SamsonovtEugeney Nassonor’Burul Dhzuzenova2Yuriy Belenkov’Valentina Nassonova2Helmut Wachter3Dietmar Fuchs34‘Inst. of Clin. Cardiol.All-Union Cardiol. Res.3rd Cherepkovskaya 15a1211552 Moskow, Russia2fr of Rheumatol.Kashirskoye Schosse 34a115552 Moskow, Russia3lnst. of Med. Chem. and Biochem.Univ. of Inns bruckFritz Pregi Str. 36020 Innsbruck, Austria Author for correspondence.Presence of EndogenousDigitalis-Like Factors In MilkTo the Editor:Endogenous factors with biologicaland immunological properties similarto digitalis drugs (endogenous digital-is-like factors, EDLF) have been foundin several tissues and body fluids ofanimals and humans, and higher con-centrations are generally observed innewborns (1-3). We recently reportedthat EDLF are present in human milk(4). To verify whether EDLF are nor-mal constituents of milk in othermammals, we measured digoxin-likeimmunoreactivity in milk pools fromsome domestic animals (horse, goat,sheep, rabbit, dog, and cow) by a pre-viously described solid-phase RIAmethod, which uses an anti-digoxinantibody (4,5). Significant EDLF con-centrations were found in the milk ofall species studied (Table 1), thus sug-gesting that EDLF may play an im-portant physiological role in the firstTable 1. EDLF ConcentrationsMeasured by RIA in Pooled MilkSamplesSource of milk EDLF conc, ng/L deHuman 61Cow 47Dog 179Goat 67Horse 64SheepRabbitdays of life in mammals and confirm-ing previous data obtained in humans(3, 4).Moreover, we measured the EDLFconcentrations in 30 milk specimensfrom 12 cows (from 6 cows, milk spec-imens were collected for 4 successivedays); the mean (± SD) EDLF concen-tration found in milk specimens ofthese cows was 46.2 ± 10.8 ng/Ldigoxin equivalents (de) (range 20.5-60.0 ng/L de). We did not find anyincrease in EDLF concentrations afterboiling the milk specimens, thus sug-gesting that EDLF are not (or wealdy)bound to milk proteins, as also previ-ously reported for human milk (4).Finally, to determine whether in-dustrial techniques for preparing arti-ficial milk formulas for babies couldaffect the EDLF concentrations, weassayed three different types of milkformulas for neonates, choosing themost popular commercial products inItaly: five formulas for preterm babies(ESPGAN 1982), eight adapted formu-las (ESPGAN 1977), and five cow-milk-based formulas (CODEX 1976)(all are powdered milk; reconstitutionwith water to the desired dilution wasdone as suggested by the manufactur-ers). No significant difference was ob-served among EDLF concentrations inthe different formulas assayed; amean EDLF value of 42.7 ± 16.9 ngfLde was found, which is very similar tothat of native cow milk (46.2 ± 10.8ng/L de), but lower than that previ-ously observed in human milk (60.6 ±4.9 ngIL de) (1).In conclusion, our data indicate that(a) EDLF are normal constituents ofmilk from humans and several typesof domestic animals; (b) industrialtechniques for the preparation of arti-ficial milk formulas for babies do notaffect EDLF concentrations present inthe native cow milk used.References1. Valdes R, Graves SW, Brown BA, LandtN. Endogenous substance in newborn in-fants causing false-positive digoxin mea-surements. J Pediatr 1983;102:947-50.2. Stone J, Bentur Y, Zalstein E, Soldin S,Giesbrecht E, Koran G. Effect of endoge-nous digoxin-like substances on the inter-pretation of high concentrations of digoxinin children. J Pediatr 1990;117:921-5.3. Biver P, Cherico A, Paci A, Baizan S,Boidrini A, Cipolloni C. Endogenous digi-talis-like factors: their possible pathophys-iological implications with particular re-gard to the perinatal period. Child NephrolUrol 1990;10:164-80.4. Cherico A, Paci A, Del Chicca MG, BiverP, Giainpietro 0. Presence of endogenousdigitalis-like factors in human milk. ChinChem 1992;38:504-6.5. Balzan S, Clerico A, Del Chicca MG,Montali U, Ghione S. Digoxin-like inunu-noreactivity in normal human plasma andurine, as detected by a solid-phase radioim-munoassay. Chin Chem 1984;30:450-1.Pascal BiverAldo Clerico’Maria Grazia Del Chicca1Gian Carlo Zucchelli’Carlo CipolloniCattedra di NeonatologiaUniversit4 degli Studi di Pisa‘Istituto di Fisiologia Clin. del CNRPisa, ItalyCoat-EffectIve Method for Detectionof “Hook Effect” in Tumor Markerimmunometrlc AssaysTo the Editor:Under certain conditions, immune-metric assays can give inaccuratemeasurements when the concentra-tion of the analyte is greatly in excessof that of the antibody. This phenom-enon, termed the “hook effect,” occurswhen the apparent concentration of anundiluted specimen with a high con-centration of analyte falls within thecalibration curve of the assay. Sand-with-type immunoassays, in which allcomponents are added simultane-ously, are particularly susceptible tothis effect. Although most analytes donot reach sufficient serum concentra-tions to be affected by the hook effect,some tumors secrete extremely largeamounts of specific proteins, used astumor markers, and give rise to thisphenomenon, in which the serum con-centration of the analyte may appearto be normal. In this laboratory wehave previously experienced the hookeffect with specimens analyzed for pro-lactin and prostate-specific antigen(PSA) (1-4). For example, the concen-tration of PSA in a specimen that was50660 pg/L was initially found tohave a concentration of 5.4 p.g/L whenundiluted (4).Although underestimations of tu-mor marker concentration due to thehook effect occur infrequently, the con-sequence of such an error has seriousmedical implications. We have triedseveral approaches to detect samplesthat display the hook effect whilemaintaining cost-effectiveness. Ourinitial strategy was to analyze all pa-tients’ specimens at a minimum of twodilutions; however, this increased thecost of analysis by 100%. As an al-ternative, we use the following strat-egy: all specimens in a run are batchedin groups of 10. As the specimens areprepared for analysis, an aliquot from

Presence of endogenous digitalis-like factors in milk

Presence of endogenous digitalis-like factors in milk

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