- Email: [email protected]
THE ANION GAP
848 what causes the virus to lodge in the central nervous system. One explanation is that HL-A3 and HL-A7 could provide a more favourable receptor site for the virus on the cell surface, leading to infection and damage of affected neurons. Another explanation is that HL-A3 and HL-A7 are linked to an immune-response gene which determines responsiveness to a cell-surface product of infection of the neuron with poliovirus. This then results in an autoimmune response to the infected central nervous system tissue. The presence of leucocytes and perivascular cuffing in central-nervous tissue in patients with paralytic poliomyelitis is compatible with this suggestion. Jersild et al.12 draw attention to the raised titres of antibody to measles virus in multiple sclerosis and show that these raised titres are seen significantly more often in patients who have HL-A3, HL-A7, or W18. As these same three antigens show an increased frequency in our patients with past paralytic poliomyelitis, we should like to suggest the possibility of a common xtiological mechanism for these two neurological disorders. Although this might be due to the action of HL-A3 and HL-A7 as favourable receptor sites on neuronal cell surfaces for viruses such as the poliovirus, a more attractive concept is that HL-A3 and HL-A7 are linked to an immune-response gene which determines the response to a common product of viral infection of central nervous tissue, namely the poliovirus in poliomyelitis and perhaps the measles virus in multiple sclerosis. Tissue
Transplantation Laboratories, Department of Surgery, University of Melbourne, Royal Melbourne Hospital, Parkville, Victoria 3050, Australia.
PETER J. MORRIS MURRAY C. PIETSCH.
factors is obscure. However, selenium has some biochemical significance as a component of glutathione peroxidase that is able to protect membrane lipids and thus the cell membrane from oxidative disintegration." The extraordinarily high sex ratios and death-rates in human myocardial infarction in Finland were also mentioned in the hypothesis.13 It was suggested that the Finnish predilection for smoked fish may at least partially explain these high figures. While this may well be the case, we should like to emphasise that the prevalence of cardiovascular diseases is highest in the eastern parts of Finland and that of M.S. in the western part of the country. More studies are therefore needed to establish the role of dietary factors in both cardiovascular and demyelinating diseases. Department of Neurology, University of Helsinki, SF-00290 Helsinki, Finland.
SIR,-A hypothesis was presented recently that human myocardial disorder may be the result of a decline in the ratio of antioxidants to polyunsaturated fatty acids.13 Nutritional muscular dystrophy (N.M.D.) was mentioned as an example of a similar condition in farm animals. The epidemiology of N.M.D. in Finland has been studied
extensively. In 1958, the disease was found to be restricted along the western coastline.14 According to the data for 1970, the frequency declined in that area while the disease became more evenly distributed in the whole
to an area
country.15 However, a small area was found within the highrisk region where a very large number of N.M.D. cases were still recorded. This small area (district of Jalasjarvi) consists of 6 rural communes and, very surprisingly, we have now discovered that the prevalence of multiple sclerosis (M.S.) is also highest in the same district (75-2 cases per 100,000 inhabitants according to the places of birth of the M.S.
patients).15
The fact that the highest prevalence of both N.M.D. and M.S. appears in the same small area of Finland may be only a coincidence. N.M.D. can be caused by a diet that contains unsaturated fatty acids inadequately protected by antioxidants.13 Lack of vitamin E and selenium 16,17 are also important pathogenetic factors. Much less is known about the xtiology of M.S. and, especially, the role of these two 12.
Jersild, C., Ammitzbøll, T., Clausen, J., Fog, T. Lancet, 1973, i,
13. 14. 15. 16. 17.
Anderson, T. W. ibid, Aug. 11, 1973, p. 298. Andersson, P. Acta path. microbiol. scand. 1960, 48, 1. Palo, J., Wikström, J., Kivalo, E. Acta neurol. scand. (in the press). MacKenzie, C. G., McCollum, E. V. J. Nutr. 1940, 20, 399. Schwarz, K., Foltz, C. M. J. Am. chem. Soc. 1957, 79, 3292.
151.
E. KIVALO.
THE ANION GAP
SIR We believe the wide reference range for anion gap mmol per 1.) Dr Miller (July 28, p.
quoted by Dr Buckley-Sharp and 206) was the result of using data from a hospital patient population, whereas that quoted by your editorial (July 7, p. 27) (less than 16 mmol per 1.) may
(7-25
refer
normal
healthy population. In our laboratory urea, and glucose are determined also using a Technicon SMA 6/60 analyser. Anion gap is calculated as serum (Na++K+)-(Cl-+HCO3-).We have calculated reference ranges for anion gap in a variety of populations using rank-order statistics: to a
serum
electrolytes,
Population Hospital patients Blood donors Volunteer staff
EPIDEMIOLOGY OF NUTRITIONAL MUSCULAR DYSTROPHY AND MULTIPLE SCLEROSIS
J. PALO J. WIKSTKÖM
25 Number Median percentile 3920 18 10 210 14 9 198 15 11
97.5
percentile 25 mmol per l. 17 mmol per1. 19 mmol per1.
These findings
highlight the fact that values for reference depend entirely on the populations from which they In those populations reasonably assumed to are derived. be comprised of normal individuals, the anion-gap reference ranges are considerably smaller than that suggested by Dr Buckley-Sharp and Dr Miller. The 198 volunteer staff were known to be in good health; not suffering from any diseases, current acute illnesses, or infections; and not taking any drugs. The selection of individuals with normal serum electrolytes and urea concentrations in no way overcomes the problem of using data from hospital patients ranges
for the calculations of normal reference ranges. Values such as serum-sodium 145, serum-potassium 4-5, serumchloride 98, and serum-bicarbonate 24 mmol per 1. are all within acceptable limits, but give an anion gap of 27 mmol per 1., a value that would be considered abnormal even by Dr Buckley-Sharp and Dr Miller. We stress the importance of using as normal a population as can reasonably be obtained for assessing reference ranges to be used as guidelines for normal limits. It is not necessary to use the anion gap as a routine quality-control device. We agree with Dr Buckley-Sharp and Dr Miller that an adequate assessment of quality control can be obtained from repeated analyses of a constant reference serum. The coefficient of variation for anion gap calculated from such data is expected to be large, as this parameter includes the analytical error of each determination included in its derivation. Thus the anion gap will not be reliable for detecting small systematic and indeterminate errors in any of these determinations. However, we believe that the anion gap calculated for each individual patient provides useful information. A high value suggests the 18.
Rotruck, J. T., Pope, A. L., Ganther, H. E., Swanson, A B. Hafeman, D. G., Hoekstra, W. G. Science, 1973, 179, 588.
849 presence of
only lactic acidosis, but also uraemia, accumulation of certain drugs, such as ketonxmia, will the to these possibilities. and alert physician salicylates, In our experience random errors in individual electrolyte determinations can be suspected from unrealistic values of the anion gap (such as a negative value). In these more broader applications the anion gap fulfils a function of quality control. not
or
Division of Clinical Chemistry, Institute of Medical and
Veterinary Science, Adelaide, South Australia.
D. W. THOMAS R. l(1. W. PAIN B. M. DUNCAN.
R.
** We have received the following reply Buckley-Sharp and Dr Miller.-ED. L.
from Dr
SIR,-We thank Dr Thomas and his colleagues for
a
sight of their comments.
We had no intention of defining a reference range of 7-25 mmol per litre for the anion gap just because these were the 3rd and 97th centiles of our whole population. Our own data show 3rd and 97th centiles of 10 and 20 mmol per litre for our restricted subset of 466 patients with normal electrolytes. These results are very similar to those of Dr Thomas’s volunteers, and probably represent a suitable reference range for
normal subjects. Dr Thomas, his colleagues, and ourselves are all agreed that your leader (July 7, p. 27) was wrong in giving an upper limit for the anion gap of 16 mmol per litre. Courtauld Institute of Biochemistry, Middlesex Hospital Medical School, London W1P 5PR.
M. D. BUCKLEY-SHARP A. L. MILLER.
Mean values for normal G.T.T., low insulin output, and insulin output obtained by computer analysis.
defined only after the results from a large number of people who have had this assay together with a G.T.T. are known. People with normal G.T.T.S and abnormal I.R.I. levels should have a yearly follow-up. Hertzler Clinic, Halstead, Kansas 67056, U.S.A.
PLASMA-INSULIN LEVELS DURING ORAL GLUCOSE LOADS IN PREDIABETICS
Sirread with great interest the article by Cerasi et al. and the correspondence which arose from it.2-5 At the Hertzler Clinic immunoreactive-insulin (I.R.I.) assays are performed on all patients who have glucosetolerance tests (G.T.T.). So far, about 1500 patients have been tested. 31 had normal glucose tolerance but their insulin output was low, and 34 had normal glucose tolerance
;
I
I:
but their insulin output was high (see accompanying figure). Of these 34 patients, 20 are of normal weight and 14 patients are overweight. Most of the 34 patients, in whom the G.T.T. and I.R.I. assay were repeated, have a family history of diabetes mellitus
p. 690.
high
SHARFUDDIN SHAH.
ACUPUNCTURE ANÆSTHESIA
SIR,—The comments which followed Dr Bull’s hypo(Aug. 25, p. 417) on acupuncture were of interest to us, because we had presentedour own experimental study of acupuncture anaesthesia and our results contradict those of Professor Andersson and his co-workers (Sept. 8, thesis
p. 564). We employed
medical students and staff as subjects and measured dental pain threshold and pain tolerance threshold to trains of graded square-wave electrical stimuli delivered to a mandibular molar or premolar. Subjects controlled stimulus intensity themselves and signalled the subjective endpoint with a buzzer. In a randomised double-blind trial, placebo altered neither pain threshold nor tolerance in 6 subjects, while 60 mg. of codeine by mouth produced statistically significant increases in pain tolerance at 90 minutes, but not in pain threshold. Mandibular nerve block with procaine caused very large increases in both. When a trained acupuncturist (R. C.) plied his art to effect maximum oral analgesia, the outcome was less impressive. After 20 minutes of vigorous needle twirling at the ipsilateral HoKu hand point, dental pain thresholds and tolerance measurements were unchanged in 4 of 5 subjects. Electrostimulation through the HoKu needle, through a needle in the mandibular area, or through both, also failed to produce a significant measure of analgesia to this form of
experimental pain. We would tentatively conclude that acupuncture as analgesia is inferior to nerve block and apparently not the equal of a modest dose of codeine. It is unsettling that similar experimental techniques should give opposite answers to different experimenters. Professor Andersson would " deny the possibility that suggestion plays any 1. National Institutes of Health Acupuncture Research Bethesda, Maryland, Feb. 28, 1973.
Conference,
Transplantation Laboratories, Department of Surgery, University of Melbourne, Royal Melbourne Hospital, Parkville, Victoria 3050, Australia.
PETER J. MORRIS MURRAY C. PIETSCH.
factors is obscure. However, selenium has some biochemical significance as a component of glutathione peroxidase that is able to protect membrane lipids and thus the cell membrane from oxidative disintegration." The extraordinarily high sex ratios and death-rates in human myocardial infarction in Finland were also mentioned in the hypothesis.13 It was suggested that the Finnish predilection for smoked fish may at least partially explain these high figures. While this may well be the case, we should like to emphasise that the prevalence of cardiovascular diseases is highest in the eastern parts of Finland and that of M.S. in the western part of the country. More studies are therefore needed to establish the role of dietary factors in both cardiovascular and demyelinating diseases. Department of Neurology, University of Helsinki, SF-00290 Helsinki, Finland.
SIR,-A hypothesis was presented recently that human myocardial disorder may be the result of a decline in the ratio of antioxidants to polyunsaturated fatty acids.13 Nutritional muscular dystrophy (N.M.D.) was mentioned as an example of a similar condition in farm animals. The epidemiology of N.M.D. in Finland has been studied
extensively. In 1958, the disease was found to be restricted along the western coastline.14 According to the data for 1970, the frequency declined in that area while the disease became more evenly distributed in the whole
to an area
country.15 However, a small area was found within the highrisk region where a very large number of N.M.D. cases were still recorded. This small area (district of Jalasjarvi) consists of 6 rural communes and, very surprisingly, we have now discovered that the prevalence of multiple sclerosis (M.S.) is also highest in the same district (75-2 cases per 100,000 inhabitants according to the places of birth of the M.S.
patients).15
The fact that the highest prevalence of both N.M.D. and M.S. appears in the same small area of Finland may be only a coincidence. N.M.D. can be caused by a diet that contains unsaturated fatty acids inadequately protected by antioxidants.13 Lack of vitamin E and selenium 16,17 are also important pathogenetic factors. Much less is known about the xtiology of M.S. and, especially, the role of these two 12.
Jersild, C., Ammitzbøll, T., Clausen, J., Fog, T. Lancet, 1973, i,
13. 14. 15. 16. 17.
Anderson, T. W. ibid, Aug. 11, 1973, p. 298. Andersson, P. Acta path. microbiol. scand. 1960, 48, 1. Palo, J., Wikström, J., Kivalo, E. Acta neurol. scand. (in the press). MacKenzie, C. G., McCollum, E. V. J. Nutr. 1940, 20, 399. Schwarz, K., Foltz, C. M. J. Am. chem. Soc. 1957, 79, 3292.
151.
E. KIVALO.
THE ANION GAP
SIR We believe the wide reference range for anion gap mmol per 1.) Dr Miller (July 28, p.
quoted by Dr Buckley-Sharp and 206) was the result of using data from a hospital patient population, whereas that quoted by your editorial (July 7, p. 27) (less than 16 mmol per 1.) may
(7-25
refer
normal
healthy population. In our laboratory urea, and glucose are determined also using a Technicon SMA 6/60 analyser. Anion gap is calculated as serum (Na++K+)-(Cl-+HCO3-).We have calculated reference ranges for anion gap in a variety of populations using rank-order statistics: to a
serum
electrolytes,
Population Hospital patients Blood donors Volunteer staff
EPIDEMIOLOGY OF NUTRITIONAL MUSCULAR DYSTROPHY AND MULTIPLE SCLEROSIS
J. PALO J. WIKSTKÖM
25 Number Median percentile 3920 18 10 210 14 9 198 15 11
97.5
percentile 25 mmol per l. 17 mmol per1. 19 mmol per1.
These findings
highlight the fact that values for reference depend entirely on the populations from which they In those populations reasonably assumed to are derived. be comprised of normal individuals, the anion-gap reference ranges are considerably smaller than that suggested by Dr Buckley-Sharp and Dr Miller. The 198 volunteer staff were known to be in good health; not suffering from any diseases, current acute illnesses, or infections; and not taking any drugs. The selection of individuals with normal serum electrolytes and urea concentrations in no way overcomes the problem of using data from hospital patients ranges
for the calculations of normal reference ranges. Values such as serum-sodium 145, serum-potassium 4-5, serumchloride 98, and serum-bicarbonate 24 mmol per 1. are all within acceptable limits, but give an anion gap of 27 mmol per 1., a value that would be considered abnormal even by Dr Buckley-Sharp and Dr Miller. We stress the importance of using as normal a population as can reasonably be obtained for assessing reference ranges to be used as guidelines for normal limits. It is not necessary to use the anion gap as a routine quality-control device. We agree with Dr Buckley-Sharp and Dr Miller that an adequate assessment of quality control can be obtained from repeated analyses of a constant reference serum. The coefficient of variation for anion gap calculated from such data is expected to be large, as this parameter includes the analytical error of each determination included in its derivation. Thus the anion gap will not be reliable for detecting small systematic and indeterminate errors in any of these determinations. However, we believe that the anion gap calculated for each individual patient provides useful information. A high value suggests the 18.
Rotruck, J. T., Pope, A. L., Ganther, H. E., Swanson, A B. Hafeman, D. G., Hoekstra, W. G. Science, 1973, 179, 588.
849 presence of
only lactic acidosis, but also uraemia, accumulation of certain drugs, such as ketonxmia, will the to these possibilities. and alert physician salicylates, In our experience random errors in individual electrolyte determinations can be suspected from unrealistic values of the anion gap (such as a negative value). In these more broader applications the anion gap fulfils a function of quality control. not
or
Division of Clinical Chemistry, Institute of Medical and
Veterinary Science, Adelaide, South Australia.
D. W. THOMAS R. l(1. W. PAIN B. M. DUNCAN.
R.
** We have received the following reply Buckley-Sharp and Dr Miller.-ED. L.
from Dr
SIR,-We thank Dr Thomas and his colleagues for
a
sight of their comments.
We had no intention of defining a reference range of 7-25 mmol per litre for the anion gap just because these were the 3rd and 97th centiles of our whole population. Our own data show 3rd and 97th centiles of 10 and 20 mmol per litre for our restricted subset of 466 patients with normal electrolytes. These results are very similar to those of Dr Thomas’s volunteers, and probably represent a suitable reference range for
normal subjects. Dr Thomas, his colleagues, and ourselves are all agreed that your leader (July 7, p. 27) was wrong in giving an upper limit for the anion gap of 16 mmol per litre. Courtauld Institute of Biochemistry, Middlesex Hospital Medical School, London W1P 5PR.
M. D. BUCKLEY-SHARP A. L. MILLER.
Mean values for normal G.T.T., low insulin output, and insulin output obtained by computer analysis.
defined only after the results from a large number of people who have had this assay together with a G.T.T. are known. People with normal G.T.T.S and abnormal I.R.I. levels should have a yearly follow-up. Hertzler Clinic, Halstead, Kansas 67056, U.S.A.
PLASMA-INSULIN LEVELS DURING ORAL GLUCOSE LOADS IN PREDIABETICS
Sirread with great interest the article by Cerasi et al. and the correspondence which arose from it.2-5 At the Hertzler Clinic immunoreactive-insulin (I.R.I.) assays are performed on all patients who have glucosetolerance tests (G.T.T.). So far, about 1500 patients have been tested. 31 had normal glucose tolerance but their insulin output was low, and 34 had normal glucose tolerance
;
I
I:
but their insulin output was high (see accompanying figure). Of these 34 patients, 20 are of normal weight and 14 patients are overweight. Most of the 34 patients, in whom the G.T.T. and I.R.I. assay were repeated, have a family history of diabetes mellitus
p. 690.
high
SHARFUDDIN SHAH.
ACUPUNCTURE ANÆSTHESIA
SIR,—The comments which followed Dr Bull’s hypo(Aug. 25, p. 417) on acupuncture were of interest to us, because we had presentedour own experimental study of acupuncture anaesthesia and our results contradict those of Professor Andersson and his co-workers (Sept. 8, thesis
p. 564). We employed
medical students and staff as subjects and measured dental pain threshold and pain tolerance threshold to trains of graded square-wave electrical stimuli delivered to a mandibular molar or premolar. Subjects controlled stimulus intensity themselves and signalled the subjective endpoint with a buzzer. In a randomised double-blind trial, placebo altered neither pain threshold nor tolerance in 6 subjects, while 60 mg. of codeine by mouth produced statistically significant increases in pain tolerance at 90 minutes, but not in pain threshold. Mandibular nerve block with procaine caused very large increases in both. When a trained acupuncturist (R. C.) plied his art to effect maximum oral analgesia, the outcome was less impressive. After 20 minutes of vigorous needle twirling at the ipsilateral HoKu hand point, dental pain thresholds and tolerance measurements were unchanged in 4 of 5 subjects. Electrostimulation through the HoKu needle, through a needle in the mandibular area, or through both, also failed to produce a significant measure of analgesia to this form of
experimental pain. We would tentatively conclude that acupuncture as analgesia is inferior to nerve block and apparently not the equal of a modest dose of codeine. It is unsettling that similar experimental techniques should give opposite answers to different experimenters. Professor Andersson would " deny the possibility that suggestion plays any 1. National Institutes of Health Acupuncture Research Bethesda, Maryland, Feb. 28, 1973.
Conference,