Annals of Clinical Biochemistry, 1979, 16, 124-126
Reliability of serum ferritin determinations after total dose infusion of iron dextran in pregnancy T. R. J. LAPPIN1, LINDA A. WHITELEyl, AND G. A. MURNAGHAN2 From the 1 Department of Haematology, Royal Victoria Hospital, Belfast and the 2 Department of Midwifery and Gynaecology, The Queen's University of Belfast, Institute of Clinical Science, Belfast BTI26BA
Serum ferritin, serum iron, total iron binding capacity, and haemoglobin levels were measured in a group of 36 pregnant women before, one week after, and four weeks after a total dose infusion of iron dextran (T.D.I.). The serum ferritin level is considered to provide a reliable index of maternal iron stores one month, but not one week, after TDI.
SUMMARY
Iron deficiency anaemia remains the commonest whether serum ferritin is a reliable index of storage medical disorder in pregnancy (Barnes, 1974), iron after a total dose infusion of iron dextran although many studies have shown conclusively (TDI) in anaemic pregnant women. that its development may be prevented by iron supplements (Lund, 1951; Gatenby, 1956; Morgan, Patients and methods 1961; Chanarin et al., 1965). This anaemia poses a particularly serious threat if haemorrhage compli- During a four-month period, 36 women were treated cates the pregnancy (McFee, 1973). Iron deficiency by TDI. These patients had an iron deficiency also causes depletion of the iron-containing com- anaemia despite the prescription of daily oral pounds in solid tissues (Beutler, 1964; Jacobs, supplements of ferrous fumarate 300 mg and folic 1969; Fairbanks et al., 1971; Dallman, 1974) in a acid 350 p.g. Their ages ranged from 19 to 44 years, manner that cannot be fully predicted from the degree and parity from 0 to 11. Thirty-two of the women of anaemia (Dallman, 1974). The available storage were first seen at the antenatal clinic before the iron may be estimated from the serum ferritin levels. twentieth week of pregnancy, and their haemoglobin Since the serum ferritin concentration becomes sub- levels, at the initial visit, ranged from 9·3 to 13'5 normal before exhaustion of mobilisable iron g/d\. The four who were seen late were booked at 20, stores, it provides a useful adjunct to the more widely 22, 24, and 33 weeks' gestation with haemoglobin used biochemical tests of iron status. levels ranging from 9'6 to 11'7 g/d\. Fifteen of the An immunoradiometric assay for ferritin in serum patients had a previous history of iron deficiency was developed by Addison et al. (1972); subse- anaemia in pregnancy and three of these had had quently, numerous methods have been described, recurrent anaemia. The haemoglobin level in all including the two-site immunoradiometric assay patients given a TDI was less than 10·2 g/dl, and (Miles et 01.,1974) and the direct radioimmunoassay the peripheral blood picture was one of iron defiusing labelled ferritin (Wide and Birgegard, 1977). ciency anaemia. The gestation period at the time of Since these methods are extremely sensitive, only TDI ranged from 26 to 39 weeks and, unless the 0·2 ml of serum is usually required for duplicate patient was close to term, no parenteral treatment determinations of the ferritin level. was given less than nine weeks after the prescription Caution is required in the interpretation of ferritin of oral iron. values. To date, two main sources of error have The dose of iron dextran (Scott and Govan, 1954) been identified: Firstly, the so-called 'high-dose hook was calculated from the formula:effect' occurs in the two-site immunoradiometric Iron required (mg) = 0·3 x W x D assay (Miles et al., 1974; Green et al., 1977). where W is the patient's weight in pounds and Dis Secondly, the level of serum ferritin rises rapidly the percentage haemoglobin deficit below 14·6 gldl. after oral iron therapy and therefore does not The dose of iron given was 1348·6 mg of iron ± accurately reflect the body iron stores (Siimes et al., 327·2 (mean ± 1 SO) in a concentration not greater 1974). than 5 % (v/v) Imferon in physiological saline. No The purpose of this investigation was to determine adverse reactions occurred during the infusions. 124
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Reliability of serum ferritin determinations after total dose infusion of iron dextran in pregnancy Peripheral blood samples were taken before the TDl and, where possible, one week (34 patients) and four weeks (36 patients) later. The haemoglobin concentration was measured on a Coulter S counter. Serum iron and total iron binding capacity were measured by a modification of the method of Young and Hicks (1965), and the reported values of serum ferritin were obtained by the immunoradiometric assay of Addison et al. (1972). The ferritin levels were also determined in parallel by the two-site radioimmunoassay using a commercial kit", taking care to look for the 'hook' effect (Green et al., 1977). There was good agreement between the results obtained in both ferritin methods.The Wilcoxon matched pair signed rank test (Siegel, 1956) was used for the comparison of the pre- and post-treatment levels of each variable. The level of significance used throughout was p < 0·05. Results The mean values of the blood tests performed are summarised in the Table. There was a significant rise Table Mean haemoglobin, serum iron, total iron binding capacity, and serum ferritin results Before TDI (n
Haemoglobin (S/dl) Serum iron (j.lmolll) TIDe (:Jmol/l) Serum ferritin (lLs/l)
~
36)
9·82 13·88 102'68 15'15
1 week later (n
~
34)
4 weeks later (n
~.
36)
10'24 p < 0·01 88·56 p < 0·002 103·15
11·23 p < 0-002 21·42 p < 0·01 87'88
NS
NS
410'33 p < 0·002
p
153·24 < 0·002
in haemoglobin levels one week after the infusion (T = 109; p < 0'01) with a highly significant rise after four weeks (T = 1'00; P < 0'002). One week after treatment the serum iron levels showed a significant rise from a mean of 13·88 fLmoljl (pre-treatment) to 88·56 fLmoljl (T = 7'50; P < 0'002). By the fourth week the levels had fallen considerably to a mean value of 21'42 fLmoljl but were still significantly greater (T = 54'50; P < 0'01) than the pre-treatment levels. Likewise, the ferritin levels showed a significant rise from a mean of 15'15 fLgjl (pre-treatment) to 410'33 /J-gjl one week after treatment (T = 0'00; P < 0'002). By the fourth week, the levels had fallen to a mean value of 153'24 fLgjl, still significantly greater (T = 0·00; P < 0'002) than the pre-treatment levels. IRamco Laboratories Inc., Houston, Texas, USA.
125
No significant difference was found between the pre- and post-treatment levels of total iron binding capacity either one week or four weeks after treatment. Discussion The increased demand for iron in pregnancy caused by the expansion of the maternal red cell mass and the developing fetus is of the order of 400 mg. This is derived from either increased iron absorption or mobilisation of maternal iron stores. The correlation established by Walters et al. (1973) that each fLg ferritinjl of serum represents 8 mg of available storage iron provides a convenient means of estimating the total body stores of iron. The average infusion of iron in this study was 1349 mg. After one month the mean haemoglobin rise was approximately 1-4 gjdl, equivalent to a total rise of about 70 g or approximately 250 mg of iron. If the demands of the fetus over this month are assumed to be 50 mg, 1050 rng of iron should remain available to enter the body stores. Using the correlation of Walters et al. (1973), the expected average rise in serum ferritin concentration in this group of patients would be approximately 131 fLgjl. The observed rise of 138 fLgjl after one month agrees well with this expected figure. The high mean level of serum ferritin of 410 p.gjl after one week therefore gives a false impression of the total iron stores. These results indicate that serum ferritin results are not a reliable index of body stores one week after TDT and that ideally the lag period for measurement of serum iron should approach one month. This result is consistent with that of Heinrich (1978) who investigated the response of serum ferritin to oral iron therapy. Heinrich concluded that there should be an interval of one to two weeks between termination of oral iron treatment and measurement of the ferritin level, if it is to be a reliable index of iron stores. Our results also confirm that many women embark on pregnancy with deficient iron stores (eg, Kelly et al., 1977). Although all our patients claimed to have taken oral iron during the study pregnancy, the amount of iron in storage reflected by the serum ferritin levels showed inadequate levels in the majority. Fenton et al. (1977) demonstrated that the demand for iron outstrips supply during pregnancy and that there is a rapid decline in iron stores from the early months. They further showed that this fall occurs in all women irrespective of the initial level of their iron stores and whether or not they receive iron supplements. They suggest that this large demand is caused by the increase in red cell mass, an event that occurs in the first trimester.
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126
T. R. J. Lappin, Linda A. Whiteley, and G. A. Murnaghan
TDI therefore constitutes an effective, convenient, and time-saving procedure for the correction of iron deficiency anaemia. When given correctly, it is rarely accompanied by general reactions (Basu, 1965). Provided there is a suitable time interval between the infusion and the determination of the serum ferritin level, this test should prove to be an extremely valuable adjunct to the tests for iron metabolism already in common use. We thank Dr J. D. Merrett for help with the statistical analysis, and Professors M. G. Nelson and J. H. M. Pinkerton for their support and valuable advice. References Addison, G. M., Beamish, M. R., Hales, C. N., Hodgkins, M., Jacobs, A., and L1ewellin, P. (1972). An immunoradiometric assay for ferritin in the serum of normal subjects and patients with iron deficiency and iron overload. Journal of Clinical Pathology, 25, 326-329. Barnes, C. G. (1974). Medical Disorders in Obstetric Practice, 4th edition, p. 175. Blackwell, Oxford and Edinburgh. Basu, S. K. (1965) Administration of iron dextran complex by continuous intravenous infusion. Journal of Obstetrics and Gynaecology of the British Commonwealth, 72, 253-258. Beutler, E. (1964). Tissue effects of iron deficiency. Iron Metabolism: An International Symposium, edited by F. Gross, p.256. Springer, Berlin. Cbanarin, I., Rothman, D., and Berry, V. (1965). Iron deficiency and its relation to folic acid status in pregnancy -results of a clinical trial. British Medical Journal, 1, 480-485. Dallman, P. (1974). Tissue effects of iron deficiency. Iron in Biochemistry and Medicine, edited by A. Jacobs, and M. WOTWood, pp, 437-475. Academic Press, London. Fairbanks, Y. F., Fahey, J. L., and Beutler, E. (1971). Clinical Disorders of Iron Metabolism, 2nd edition, p. 229. Grune and Stratton, New York. Fenton, Y., Cavill, I., and Fisher, J. (1977). Iron stores in pregnancy. British Journal of Haematology; 37, 145-149 ", Gatenby, P. B. B. (1956). The anaemias of pregnancy In
Dublin (iron deficiency anaemia in pregnancy). Proceedings of the Nutrition Society, 15, 115-1 19. Green, R., Watson, L. R., Saab, G. A., and Crosby, W. M. (1977). 'Normal' serum ferritin-s-a caution. Blood, 50, 545-547. Heinrich, H. C. (1978). 'Normal' serum ferritin-another caution. Blood, 51, 764-765. Jacobs, A. (1969). Tissue changes in iron deficiency (annotation). British Journal of Haematology, 16, 1-8. Kelly, A. M., McDonald, D. J., and McNay, M. B. (1977). Ferritin as an assessment of iron stores in normal pregnancy. British Journal of Obstetrics and Gynaecology, 84, 434-438. Lund, C. J. (1951). Studies on the iron deficiency anaemia of pregnancy including plasma volume, total haemoglobin. erythrocyte, protoporphyrin in treated and untreated normal and anaemic patients. American Journal of Obstetrics and Gynecology, 62, 947-963. Me Fee, J. G. (1973). Anaemia: a high-risk complication of pregnancy. Clinics in Obstetrics and Gynecology, 16, 153171. Miles, L. E. M., Lipschitz, D. A., Bieber, C. P., and Cook, J. D. (1974). Measurement of serum ferritin by a 2-site immunoradiometric assay. Analytical Biochemistry, 61, 209-224. Morgan, E. H. (1961). Plasma iron and haemoglobin levels in pregnancy-i-the effect of oral iron. Lancet, 1, 9-12. Scott, J. M., and Govan, A. D. T. (195~). Anaemia of pregnancy treated with intramuscular iron. British Medical Journal,2, 1257-1259. Siegel, S. (1956). Non-parametric statistics for the behavioural Sciences, pp. 75-83. McGraw Hill, Kogakusha, Tokyo. Siimes M. A., Addiego, J. E., and Dallman, P. R. (1974). Perritin in serum: diagnosis of iron deficiency and iron overload in infants and children. Blood, 43, 581-590. Walters, G. 0., Miller, F. M., and Worwood, M. (1973). Serum ferritin concentration and iron stores in normal subjects. Journal of Clinical Pathology, 26, 770-772. Wide, L., and Birgegard, G. A. (1977). A solid phase radioimmunoassay for serum ferritin using ""I-labelled ferritin. Uppsala Journal of Medical Science, 82,15-19. Young, D. S., and Hicks, J. M. (1965). Methods for the automatic determination of serum iron. Journal of Clinical Pathology, 18,98- 102. Accepted for publication 21 February /979
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Reliability of serum ferritin determinations after total dose infusion of iron dextran in pregnancy T. R. J. LAPPIN1, LINDA A. WHITELEyl, AND G. A. MURNAGHAN2 From the 1 Department of Haematology, Royal Victoria Hospital, Belfast and the 2 Department of Midwifery and Gynaecology, The Queen's University of Belfast, Institute of Clinical Science, Belfast BTI26BA
Serum ferritin, serum iron, total iron binding capacity, and haemoglobin levels were measured in a group of 36 pregnant women before, one week after, and four weeks after a total dose infusion of iron dextran (T.D.I.). The serum ferritin level is considered to provide a reliable index of maternal iron stores one month, but not one week, after TDI.
SUMMARY
Iron deficiency anaemia remains the commonest whether serum ferritin is a reliable index of storage medical disorder in pregnancy (Barnes, 1974), iron after a total dose infusion of iron dextran although many studies have shown conclusively (TDI) in anaemic pregnant women. that its development may be prevented by iron supplements (Lund, 1951; Gatenby, 1956; Morgan, Patients and methods 1961; Chanarin et al., 1965). This anaemia poses a particularly serious threat if haemorrhage compli- During a four-month period, 36 women were treated cates the pregnancy (McFee, 1973). Iron deficiency by TDI. These patients had an iron deficiency also causes depletion of the iron-containing com- anaemia despite the prescription of daily oral pounds in solid tissues (Beutler, 1964; Jacobs, supplements of ferrous fumarate 300 mg and folic 1969; Fairbanks et al., 1971; Dallman, 1974) in a acid 350 p.g. Their ages ranged from 19 to 44 years, manner that cannot be fully predicted from the degree and parity from 0 to 11. Thirty-two of the women of anaemia (Dallman, 1974). The available storage were first seen at the antenatal clinic before the iron may be estimated from the serum ferritin levels. twentieth week of pregnancy, and their haemoglobin Since the serum ferritin concentration becomes sub- levels, at the initial visit, ranged from 9·3 to 13'5 normal before exhaustion of mobilisable iron g/d\. The four who were seen late were booked at 20, stores, it provides a useful adjunct to the more widely 22, 24, and 33 weeks' gestation with haemoglobin used biochemical tests of iron status. levels ranging from 9'6 to 11'7 g/d\. Fifteen of the An immunoradiometric assay for ferritin in serum patients had a previous history of iron deficiency was developed by Addison et al. (1972); subse- anaemia in pregnancy and three of these had had quently, numerous methods have been described, recurrent anaemia. The haemoglobin level in all including the two-site immunoradiometric assay patients given a TDI was less than 10·2 g/dl, and (Miles et 01.,1974) and the direct radioimmunoassay the peripheral blood picture was one of iron defiusing labelled ferritin (Wide and Birgegard, 1977). ciency anaemia. The gestation period at the time of Since these methods are extremely sensitive, only TDI ranged from 26 to 39 weeks and, unless the 0·2 ml of serum is usually required for duplicate patient was close to term, no parenteral treatment determinations of the ferritin level. was given less than nine weeks after the prescription Caution is required in the interpretation of ferritin of oral iron. values. To date, two main sources of error have The dose of iron dextran (Scott and Govan, 1954) been identified: Firstly, the so-called 'high-dose hook was calculated from the formula:effect' occurs in the two-site immunoradiometric Iron required (mg) = 0·3 x W x D assay (Miles et al., 1974; Green et al., 1977). where W is the patient's weight in pounds and Dis Secondly, the level of serum ferritin rises rapidly the percentage haemoglobin deficit below 14·6 gldl. after oral iron therapy and therefore does not The dose of iron given was 1348·6 mg of iron ± accurately reflect the body iron stores (Siimes et al., 327·2 (mean ± 1 SO) in a concentration not greater 1974). than 5 % (v/v) Imferon in physiological saline. No The purpose of this investigation was to determine adverse reactions occurred during the infusions. 124
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Reliability of serum ferritin determinations after total dose infusion of iron dextran in pregnancy Peripheral blood samples were taken before the TDl and, where possible, one week (34 patients) and four weeks (36 patients) later. The haemoglobin concentration was measured on a Coulter S counter. Serum iron and total iron binding capacity were measured by a modification of the method of Young and Hicks (1965), and the reported values of serum ferritin were obtained by the immunoradiometric assay of Addison et al. (1972). The ferritin levels were also determined in parallel by the two-site radioimmunoassay using a commercial kit", taking care to look for the 'hook' effect (Green et al., 1977). There was good agreement between the results obtained in both ferritin methods.The Wilcoxon matched pair signed rank test (Siegel, 1956) was used for the comparison of the pre- and post-treatment levels of each variable. The level of significance used throughout was p < 0·05. Results The mean values of the blood tests performed are summarised in the Table. There was a significant rise Table Mean haemoglobin, serum iron, total iron binding capacity, and serum ferritin results Before TDI (n
Haemoglobin (S/dl) Serum iron (j.lmolll) TIDe (:Jmol/l) Serum ferritin (lLs/l)
~
36)
9·82 13·88 102'68 15'15
1 week later (n
~
34)
4 weeks later (n
~.
36)
10'24 p < 0·01 88·56 p < 0·002 103·15
11·23 p < 0-002 21·42 p < 0·01 87'88
NS
NS
410'33 p < 0·002
p
153·24 < 0·002
in haemoglobin levels one week after the infusion (T = 109; p < 0'01) with a highly significant rise after four weeks (T = 1'00; P < 0'002). One week after treatment the serum iron levels showed a significant rise from a mean of 13·88 fLmoljl (pre-treatment) to 88·56 fLmoljl (T = 7'50; P < 0'002). By the fourth week the levels had fallen considerably to a mean value of 21'42 fLmoljl but were still significantly greater (T = 54'50; P < 0'01) than the pre-treatment levels. Likewise, the ferritin levels showed a significant rise from a mean of 15'15 fLgjl (pre-treatment) to 410'33 /J-gjl one week after treatment (T = 0'00; P < 0'002). By the fourth week, the levels had fallen to a mean value of 153'24 fLgjl, still significantly greater (T = 0·00; P < 0'002) than the pre-treatment levels. IRamco Laboratories Inc., Houston, Texas, USA.
125
No significant difference was found between the pre- and post-treatment levels of total iron binding capacity either one week or four weeks after treatment. Discussion The increased demand for iron in pregnancy caused by the expansion of the maternal red cell mass and the developing fetus is of the order of 400 mg. This is derived from either increased iron absorption or mobilisation of maternal iron stores. The correlation established by Walters et al. (1973) that each fLg ferritinjl of serum represents 8 mg of available storage iron provides a convenient means of estimating the total body stores of iron. The average infusion of iron in this study was 1349 mg. After one month the mean haemoglobin rise was approximately 1-4 gjdl, equivalent to a total rise of about 70 g or approximately 250 mg of iron. If the demands of the fetus over this month are assumed to be 50 mg, 1050 rng of iron should remain available to enter the body stores. Using the correlation of Walters et al. (1973), the expected average rise in serum ferritin concentration in this group of patients would be approximately 131 fLgjl. The observed rise of 138 fLgjl after one month agrees well with this expected figure. The high mean level of serum ferritin of 410 p.gjl after one week therefore gives a false impression of the total iron stores. These results indicate that serum ferritin results are not a reliable index of body stores one week after TDT and that ideally the lag period for measurement of serum iron should approach one month. This result is consistent with that of Heinrich (1978) who investigated the response of serum ferritin to oral iron therapy. Heinrich concluded that there should be an interval of one to two weeks between termination of oral iron treatment and measurement of the ferritin level, if it is to be a reliable index of iron stores. Our results also confirm that many women embark on pregnancy with deficient iron stores (eg, Kelly et al., 1977). Although all our patients claimed to have taken oral iron during the study pregnancy, the amount of iron in storage reflected by the serum ferritin levels showed inadequate levels in the majority. Fenton et al. (1977) demonstrated that the demand for iron outstrips supply during pregnancy and that there is a rapid decline in iron stores from the early months. They further showed that this fall occurs in all women irrespective of the initial level of their iron stores and whether or not they receive iron supplements. They suggest that this large demand is caused by the increase in red cell mass, an event that occurs in the first trimester.
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126
T. R. J. Lappin, Linda A. Whiteley, and G. A. Murnaghan
TDI therefore constitutes an effective, convenient, and time-saving procedure for the correction of iron deficiency anaemia. When given correctly, it is rarely accompanied by general reactions (Basu, 1965). Provided there is a suitable time interval between the infusion and the determination of the serum ferritin level, this test should prove to be an extremely valuable adjunct to the tests for iron metabolism already in common use. We thank Dr J. D. Merrett for help with the statistical analysis, and Professors M. G. Nelson and J. H. M. Pinkerton for their support and valuable advice. References Addison, G. M., Beamish, M. R., Hales, C. N., Hodgkins, M., Jacobs, A., and L1ewellin, P. (1972). An immunoradiometric assay for ferritin in the serum of normal subjects and patients with iron deficiency and iron overload. Journal of Clinical Pathology, 25, 326-329. Barnes, C. G. (1974). Medical Disorders in Obstetric Practice, 4th edition, p. 175. Blackwell, Oxford and Edinburgh. Basu, S. K. (1965) Administration of iron dextran complex by continuous intravenous infusion. Journal of Obstetrics and Gynaecology of the British Commonwealth, 72, 253-258. Beutler, E. (1964). Tissue effects of iron deficiency. Iron Metabolism: An International Symposium, edited by F. Gross, p.256. Springer, Berlin. Cbanarin, I., Rothman, D., and Berry, V. (1965). Iron deficiency and its relation to folic acid status in pregnancy -results of a clinical trial. British Medical Journal, 1, 480-485. Dallman, P. (1974). Tissue effects of iron deficiency. Iron in Biochemistry and Medicine, edited by A. Jacobs, and M. WOTWood, pp, 437-475. Academic Press, London. Fairbanks, Y. F., Fahey, J. L., and Beutler, E. (1971). Clinical Disorders of Iron Metabolism, 2nd edition, p. 229. Grune and Stratton, New York. Fenton, Y., Cavill, I., and Fisher, J. (1977). Iron stores in pregnancy. British Journal of Haematology; 37, 145-149 ", Gatenby, P. B. B. (1956). The anaemias of pregnancy In
Dublin (iron deficiency anaemia in pregnancy). Proceedings of the Nutrition Society, 15, 115-1 19. Green, R., Watson, L. R., Saab, G. A., and Crosby, W. M. (1977). 'Normal' serum ferritin-s-a caution. Blood, 50, 545-547. Heinrich, H. C. (1978). 'Normal' serum ferritin-another caution. Blood, 51, 764-765. Jacobs, A. (1969). Tissue changes in iron deficiency (annotation). British Journal of Haematology, 16, 1-8. Kelly, A. M., McDonald, D. J., and McNay, M. B. (1977). Ferritin as an assessment of iron stores in normal pregnancy. British Journal of Obstetrics and Gynaecology, 84, 434-438. Lund, C. J. (1951). Studies on the iron deficiency anaemia of pregnancy including plasma volume, total haemoglobin. erythrocyte, protoporphyrin in treated and untreated normal and anaemic patients. American Journal of Obstetrics and Gynecology, 62, 947-963. Me Fee, J. G. (1973). Anaemia: a high-risk complication of pregnancy. Clinics in Obstetrics and Gynecology, 16, 153171. Miles, L. E. M., Lipschitz, D. A., Bieber, C. P., and Cook, J. D. (1974). Measurement of serum ferritin by a 2-site immunoradiometric assay. Analytical Biochemistry, 61, 209-224. Morgan, E. H. (1961). Plasma iron and haemoglobin levels in pregnancy-i-the effect of oral iron. Lancet, 1, 9-12. Scott, J. M., and Govan, A. D. T. (195~). Anaemia of pregnancy treated with intramuscular iron. British Medical Journal,2, 1257-1259. Siegel, S. (1956). Non-parametric statistics for the behavioural Sciences, pp. 75-83. McGraw Hill, Kogakusha, Tokyo. Siimes M. A., Addiego, J. E., and Dallman, P. R. (1974). Perritin in serum: diagnosis of iron deficiency and iron overload in infants and children. Blood, 43, 581-590. Walters, G. 0., Miller, F. M., and Worwood, M. (1973). Serum ferritin concentration and iron stores in normal subjects. Journal of Clinical Pathology, 26, 770-772. Wide, L., and Birgegard, G. A. (1977). A solid phase radioimmunoassay for serum ferritin using ""I-labelled ferritin. Uppsala Journal of Medical Science, 82,15-19. Young, D. S., and Hicks, J. M. (1965). Methods for the automatic determination of serum iron. Journal of Clinical Pathology, 18,98- 102. Accepted for publication 21 February /979
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