281 of
an
infant with
a
large myelocoele after
slightly Campbell a
raised et awl.4 raised
had been recorded. amniotic-fluid terminated an apparently normal pregnancy after a A.F.P. had been observed, and this error was presumably due to fetal-blood contamination of the amniotic-fluid sample.5 It has been shown that the macrophage count in amniotic fluid is raised in cases of open c.N.s. lesions. 6,7 Although this test cannot be regarded as diagnostic because false-positive results may occur, no false-negative findings have been recorded. Since the macrophage count of an A.F.P.
amniotic fluid can be determined simply6 and is not affected by either fetal or maternal blood contamination, it should provide a useful adjunct to the antenatal diagnosis of open C.N.S. lesions. This will apply especially in cases where the amniotic fluid contains fetal blood and where A.F.P. levels are equivocal and/or at variance with ultrasonic
findings. Cytogenetics Unit, Department of Histopathology, Adelaide Children’s Hospital, North Adelaide, South Australia, 5006, Australia.
GRANT R. SUTHERLAND.
SIR,-Like
Dr Lrilman and his
obtained (and all of the patients on chemotherapy yielded the remaining 16 smear-positive culture-negative results) had other specimens from which tubercle bacilli were grown. A genuine false positive occurred in only 1 specimen, a liver biopsy which had been ground with sterile distilled water obtained from a supply of deionised water distributed through black plastic piping. Centrifuged specimens of this water were found to contain acid-fast bacilli. Deionised water systems are an unusual source of contamination, possibly relevant to the investigation of Weinstein et al. We conclude that direct-smear examination in our hands has been a remarkably specific test and that genuine false
colleagues (May 31,
positives "
false
positives resulting
to
be of great value in the
the low yield of Salmonella typhi from urine reported by Dr Gilman and his associates. The statement that excretion of typhoid bacilli in the urine is common in the late stage of typhoid fever belongs to the pre-antibiotic era, but has not been corrected even in the latest editions of textbooks of bacteriology and infectious diseases. It has been our experience during the past 20 years that urine cultures are rarely positive in adequately treated patients. This may change again in areas where antibiotic-resistant strains of S. typhi are common. In countries where sensitive strains are predominant, positive urine cultures may suggest the development of a focus in a damaged or obstructed kidney.
G. ALTMANN.
FALSE-POSITIVE ACID-FAST SMEARS SIR,-While the article by Dr Weinstein and his p. 173) reminds us of the value of prompt detective work in uncovering laboratory error, the impression is given that smear examination is often an unreliable procedure. Thus " false positives ", operationally defined by the authors as smear-positive, culture-negative specimens from patients not on chemotherapy, were said to occur in 0-1-5% of all specimens examined and in 3-55% of smear-positive specimens-the proportion in their own results being 4-1%. We have therefore examined our own data over the past two years. Out of a total of 7774 unselected specimens of all types examined by direct
colleagues (July 26,
smear
and culture for mycobacteria, 248 yielded a and, of these, 19 failed to grow on culture.
positive
Of the 19 smear-positive culture-negative specimens, only 3 were from patients not on chemotherapy, so that " false positives " were obtained from 0-04% of all specimens and 1-2% of smear-positive specimens-proportions lower than any quoted. Furthermore, the patients from whom 2 of the 3
smear
Kitau, M. J., Leighton, P., Gordon, Y. B., Chard, T. ibid. p. 1336. Sutherland, G. R., Brock, D. J. H., Scrimgeour, J. B. J. med. Genet. 1975, 12, 135. 7. Nelson, M. M., Orford, J., Ruttiman, M-T. S. Afr. med. J. 1975,
5. 6.
49, 72.
smears
laboratory
are
seen.
Department of Bacteriology, Royal Postgraduate Medical School, Du Cane Road, London W12 0HS.
RUTH S. MITCHISON B. W. ALLEN D. A. MITCHISON.
diagnosis of
typhoid fever, especially in children who received antibiotics before admission to hospital. I was interested in
Chaim Sheba Medical Center, Tel Hashomer, and Tel Aviv University, Tel Aviv, Israel.
from
error are exceedingly prepared directly from sputum specimens on new glass slides, stained with auramine, and examined by fluorescence microscopy, a very specific procedureavoiding some of the pitfalls which beset the conventional Ziehl-Neelsen stain. Smears (except those from cerebrospinal fluid) are only reported as positive if at least 3 acid-fast bacilli with convincing morphology have
Our
rare.
1211), the paediatricians of this hospital have found
bone-marrow culture
were
who
been
DIAGNOSIS OF TYPHOID FEVER p.
"
TERMINATION OF PREGNANCY SIR,-The H.C.S.A. will fight for the independence of the profession and will oppose any attempt to manipulate the practice of medicine for reasons of temporary political
expediency. The Association’s Council regards the directive2 issued by the Chief Medical Officer of the Department of Health to regional medical officers on Feb. 19, 1975, as such an attempt. It states that when certain consultant posts in obstetrics and gynaecology, anaathetics, and psychiatry fall vacant, applicants should be appointed only if they are personally prepared to advise on, undertake, or participate in the termination of pregnancy. The Council believes that this advice constitutes a potential threat to both professional and personal freedom. I was surprised and concerned to discover that the directive was sent out with the agreement of the Joint Consultants Committee.22 Parliament will determine when abortion is permissible, but it would surely be intolerable for participation in termination of pregnancy to be made compulsory for consultants. The Chief Medical Officer’s letter is the thin end of the wedge of compulsion and my Council has resolved to resist the directive with all the power at its disposal. Accordingly, our members will be advised to do all they can to prevent its implementation. Hospital Consultants and Specialists Association, The Old Court House, London Road, Ascot, Berkshire SL5 7EN.
N. A. SIMMONS, President.
INDIRECT LIVER LYMPHOGRAPHY
SiR,—A retrograde cannulation of the common bileduct a balloon-tipped catheter through a flexible duodenoscope, as described by Dr Shapiro and Dr Cotton (July 5, p. 13), may make possible indirect liver lymphography, displaying the hepatic lymph drainage. In the past, radiographic investigation of the lymph drainage of internal organs has not been possible, because indirect lymphography could not provide adequate pictures. Indirect liver lymphography under general anaesthesia was performed in 9 cholecystectomised dogs: through a
with
1. Bennedsen, J., Larsen, S. O. 2. Br. med. J. 1975, ii, 761.
Scand. J. resp. Dis. 1966, 47,
114.