incidence of paraproteinaemia in blood donors

Vox Sang. 39: 37-43 (1980)

Incidence of Paraproteinaemia in Blood Donors

A . Pezzoli, E. Pascali and T . Zacchi Istituto di Clinica Medica Generale, Universith di Trieste, and Centro Immunotrasfusionale, Ospedali Riuniti di Trieste, Trieste, Italy

Abstract. Paraproteinaemia was detected by agarose gel electrophoresis in 13 out of 3,800 apparently healthy blood donors of an Italian district. None of the subjects with a serum M component developed overt B cell malignancy over a prolonged period of observation. The incidence of paraproteinaemia was higher than that reported from previous surveys of similar populations of blood donors in other European countries, possibly due to the sensitivity of the technique adopted for the screening investigation. The main implications of the detection of monoclonal immunoglobulin abnormalities are briefly discussed with particular reference to the possible indications for routine screening of blood donors for the presence of paraproteins.

Introduction

It is well known that the discovery of a serum M component (or paraprotein) can- not be regarded as synonymous with myeloma or related malignant immunoprolifera- tive diseases. Paraproteins have been en- countered in association with a wide variety of conditions rather heterogeneous with respect to aetiology and pathogenesis and also in apparently healthy persons [l, 3,7, 10,

The increasing use of routine serum protein electrophoresis has revealed that the occurrence of an M component is not uncom- mon. However, the incidence of paraproteinaemia is still controversial, since some

20,24,28-301.

difficulties may arise when comparing the data reported in different published series. The frequency with which M components are detected appears to vary considerably depending on the composition of the populations studied, especially with respect to age distribution and state of health [l, 7, 13, 14, 24,28,30].

In spite of the development during the last few years of more sophisticated techniques of protein analysis, the simple electrophoretic separation of serum proteins followed by visual inspection of the pattern re- mains an indispensable tool in screening for monoclonal immunoglobulin abnormalitities [8, 13, 18,231. However, improved electrophoretic techniques, capable of better reso-

PezzoliRascalPZacchi 38

lution of the individual protein zones, can enable demonstration of very small amounts of paraprotein and recognition of homogeneous immunoglobulins which are otherwise likely to remain undetected because of their mobility among the classical major zones.

Agarose gel electrophoresis, particularly when performed according to the technique described by Johansson [ll], owing to its resolving capacity can be regarded as a highly sensitive means of detecting M components [8, 17, 18,23,27].

The results obtained by applying this technique in a survey for paraproteinaemia of blood donors of an Italian district are reported and compared with those of similar previous investigations.

Materials and Methods

Serum samples were collected from 3,800 consecutive unselected blood donors (3,247 men and 553 women) aged between 18 and 65 years. All these subjects were regular, apparently healthy, donors of the district of Trieste (Italy).

Total protein concentrations were determined by the biuret method. Screening investigation was carried out by agarose gel electrophoresis according to Johansson’s [ll] technique. Paraprotein amount was estimated by densitometric scanning. Monoclonal immunoglobulins were typed by immunoelectrophoresis [26], performed in 1.5% agar gel in the same electrophoresis buffer. Serum immunoglobulins (IgG, IgA, IgM) belonging to classes other than the paraproteins were estimated by the single radial immunodiffusion technique 1191, using agarose plates prepared in our laboratory. Anti-whole human serum and monospecific sera, anti-heavy and light immunoglobulin chains were obtained from commercial sources (Dakopatts, Copenhagen, and Behringwerke, Marburgkahn). Screening for Bence Jones proteinuria was performed by electrophoresis, followed by immunoelectrophoresis of fresh urines after concentration (up to 400 times or more) by dialysis against poly-

ethylene glycol (mean molecular weight 35,000) in 18/32 in. Visking tubing.

The first collection of specimens and screening of all blood donors were completed within 6 months. Donors proven to possess a serum M component have been followed up at intervals for 5 years. On each consecutive reexamination, the same above-mentioned procedures were used.

Routine laboratory findings, including chemical and hematological values, serological examinations and urine analysis, were periodically available. Additional special investigations, such as bone marrow and skeletal axis X-ray examinations, were not performed for ethical reasons.

The results of the study are summarized in table I. Paraproteinaemia was detected by agarose gel electrophoresis and confirmed by immunoelectrophoresis in 13 (0.34%) out of 3,800 blood donors. All the subjects bear- ing a serum M component were men, aged between 28 and 65 years. The incidence of paraproteinaemia increased with age and was highest in subjects aged 60-65, the smallest group in this series. Most paraproteins (70%) were present at a concentration lower than 2 g / lOO ml. Classification by immunoelectrophoresis showed a great preva- lence (85%) of paraproteins belonging to the IgG class. The light chain of the M component was of the x-type in 10 cases and of the A-type in 3 cases. Cryoglobulinaemia was not associated with paraproteinaemia in any do- nor.

Subsequent reexaminations over a 5-year period have confirmed the serum M component in all cases, without evidence of increasing concentration compared with the initial concentration. Serum levels of the immunoglobulins of classes other than the paraproteins were within the local normal ranges

Paraproteinaemia in Blood Donors 39

Table I. Monoclonal gammopathies in 3,800 blood donors of the district of Trieste (Italy)

Patients with monoclonal gammopathies

YO n

Incidence (n = 3,800) Sex distribution

Males (n = 3,247) Females (n = 553)

18-29 years 30-39 years 40-49 years 50-59 years 60-65 years

<2 g/100 ml >2 g/100 ml

IgG x IgG 1 IgM x

Age distribution

Paraprotein concentration

Immunochemical type

Cryoglobulinaemia Transient paraproteinaemia Gradual increase in paraprotein Immunosuppression Bence Jones proteinuria

Blood groups' 0 A B AB Rh+ Rh-

13

13 0

1 3 2 5 2

9 4

8 3 2

0 0 0 0 0

0.34

0.40 0

0.07 0.2 0.3 1.6 8.7

46 (42) 31 (39) 15 (14) 8 (5)

77 (81) 23 (19)

The total protein range was 6.3-10.3 g/lOO ml. Normal distribution in parentheses.

per sex and age and did not show any significant decrease throughout the time of observation. Bence Jones proteinuria has never been demonstrated in any donor with para-

proteinaemia. Routine laboratory findings were within normal limits. Although no bone marrow and skeletal axis x-ray examinations were carried out, B cell malignancy appears to be highly improbable in our donors with paraproteinaemia. This opinion seems justified by the steady level of the M components over a 5-year period, by the absence of immunosuppression and Bence Jones proteinuria, which are altogether in contrast with the malignant character of the monoclonal gammopathies [9, 13, 15,20,25, 28,301. It should be pointed out, however, that definitive conclusions will probably re- quire a very protracted follow-up [13, 15, 22,25,30].

Unlike the finding of Kohn and Srivastava [14], who reported a preponderance of blood group A in donors with paraproteinaemia, in our cases with monoclonal gammopathy there was no significant deviation from the normal distribution of the ABO profiles. No correlation has been observed between presence of M component and number of blood donations.

Discussion

The incidence of M components in our blood donors is similar to the 0.38% re- corded in males below 60 years of age from a natural population [ 11. This incidence, however, is higher than those reported from previous surveys of blood donors in France and in England (table 11).

It has already been pointed out that in- terpretation of population surveys and com- parison of different case materials need some caution owing to various factors which can influence to a great extent the frequency of M components [13,24]. Significant differ-

40 PezzolflascalVZacchi

Table II. Incidence of paraproteinaemia in blood donors

Geographical region Age Number Screening Monoclonal gammopathies and authors group examined method

overall incidence overt B cell malignancy

n Yo %

Fine et al. [4-61, France Cannes 21-60 1,580 FPE 1 0.06 0.0 Paris 25-60 17,419 CAE(?m) 24 0.14 0.02 St-Nazaire 25-60 3,100 CAE(?m) 10 0.32 0.03 La Rochelle 18-60 7,000 CAE-m 12 0.17 0.03 Strasbourg 18-60 4,000 CAE-m 3 0.07 0.0 Lyon 18-60 3,000 CAE-m 1 0.03 0.0 Lille 18-60 1,496 CAE-m 1 0.07 0.0

Kohn and Srivnstava [14], England, London 20-62 9,420 CAE 19 0.20 0.0

Cooke [3], England, London ? 10,Ooo ?CAE 0 0.0 0.0 Present series, Italy, Trieste 18-65 3,800 AGE 13 0.34 0.0

FPE = Filter paper electrophoresis; CAE =cellulose acetate electrophoresis; CAE-m =cellulose acetate electrophoresis micromethod ; AGE = agarose gel electrophoresis.

ences in the composition of the blood donor populations surveyed, especially with respect to age distribution, do not seem, however, to account for the higher proportion of paraproteins found in our series. The data presented by Fine et al. [4-61 from different Blood Transfusion Centres in France - and particularly the findings in people from the St-Nazaire area [6] - suggest that the incidence of paraproteinaemia could also be somehow related to the geographical origin of the population studied.

Nevertheless, the sensitivity of the technique adopted for the screening investigation is probably critical in influencing the incidence of M components. In fact, subopti- mal electrophoretic techniques may fail to

demonstrate small amounts of paraproteins. It is of interest in this regard that in two surveys on the incidence of paraproteinaemia [30] 33 out of 7 2 M components were detected by electrophoretic analysis, but the remaining 39 would have been missed if immunoelectrophoresis had not been performed as well. It is therefore probable that the figures on the incidence of paraproteinaemia which have been reported from systematic investigations performed by means of procedures of limited resolving capacity (like the ‘microzone’ techniques) are underestima- tions.

The increased frequency of monoclonal gammopathies resulting from the use of more sensitive electrophoretic techniques


may reflect an increased recognition of ‘benign’ forms, which appear to be more frequently associated with low levels of paraprotein [2, 9, 13, 15, 20, 25, 28, 301. Al- though the extensive application of screening procedures which enable detection of an increasing number of monoclonal immunoglobulins may arise more diagnostic prob- lems, the physiopathological and clinical implications of the discovery of a paraprotein, even at very low concentration, should not be disregarded. Detection of such an M component should warrant further investigations and subsequent reexaminations, not only because it is of obvious importance to assess whether the underlying immunocyte abnormality is likely to be malignant or benign. Increasing evidence is accumulating, which suggests that subjects with ‘benign’ (non-myelomatous) paraproteinaemia may be more susceptible to other diseases than the normal population and that an unex- plained M component may be an early sign of a potentially curable occult disease [7, 10, 15,20,29,30].

Surveys of blood donors confirm the occurrence of paraproteinaemia in apparently healthy subjects of adult and pre-geriatric age, but also rise a practical problem in de- ciding how donors with paraproteinaemia are to be considered with respect to blood donation. In view of the possible transmissibility of myelomatosis [21], Kohn [12] suggested that blood from donors in whom paraproteins have been detected should not be used for transfusion. Although most paraproteinaemias detected by chance in otherwise normal and healthy persons are probably to be regarded as benign, Kohn’s sug- gestion appears fully justified if we consider that, at present, there are no absolutely reliable criteria for establishing with certainty

at the time of the discovery that a paraprotein is benign and a malignant immunocyte disease will not develop [9,13,15,25,28, 301. Some apparently benign paraproteinaemias may be latent (or a prodromal stage of) myelomas remaining symptomless for a very long time, and malignant evolution has been reported to occur occasionally after many years of apparent benignity [7, 15, 16,22, 281.

Such implications, as well as evidence that monoclonal immunoglobulins in concentrations sufficient for them to be detected by a convenient routine electrophoretic technique can be found in a non-negligible percentage, would indicate screening of blood donors for paraproteinaemias. More- over, screening and long-term follow-up of large series of blood donors from different geographical areas could contribute further in understanding the natural history of ‘benign’ (idiopathic, asymptomatic) monoclonal gammopathies. People apparently in good health, such as blood donors, may provide a valuable case material for follow-up studies to establish whether development of clinical disease could be correlated with preex- isting monoclonal immunoglobulin abnormalities [14].

However, in order not to underrate the frequency of occurrence of M components, it is advisable to standardize the screening procedures and give preference to routine electrophoretic techniques capable of increased separation and resolution of individual protein zones. The widespread application of comparably sensitive procedures could enable more reliable comparisons of similar populations from different geographical areas by allowing to minimize the inter- series discrepancies imputable to purely technical factors.

42 Pezzoli/Pascali/Zacchi

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Received: April 13, 1979 Accepted: April 10, 1980

Dr. A. Pezzoli, Istituto di Clinica Medica Generale, Universith di Trieste, Ospedale Maggiore, via Stuparich 1, 1-34129 Trieste (Italy)

incidence of paraproteinaemia in blood donors

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