812

Khuroo and colleagues’ series, suggesting that women may in someway be more prone to the morbidity of intestinal helminthiasis,especially ascariasis.

Department of Medicine,Hospital Universiti Sains Malaysia,16150 Kubang Kerian,Kelatan, Malaysia

S. MAHENDRA RAJSIVA SIVAKUMARANS. VIJAYAKUMARI

Improved results with PCR for chronicmyeloid leukaemia

SIR,-We found a high frequency of false-positive results in a studyin which ten centres in Europe and North America used thepolymerase chain reaction (PCR) to look for leukaemia-specificbcrlabl transcripts in chronic myeloid leukaemia (CML) cell linesand negative controls.’ In a second study similar material wasdistributed to see whether false positives could be reduced and if thesource of any contamination could be identified. Groups were askedto adhere to the precautions recommended by Kwok and Higushi2and to run a standardised set of negative controls.Ten samples were distributed in two sets of five (batches A and B)

prepared from leukaemia cell lines. In batch A two samples ofundiluted bcrlabl positive material both contained the b2a2

transcript and three samples were ber/abl negative. In batch B threesamples contained dilutions of cells with the b3a2 transcript intober/ abl negative cells in ratios of 1 in 104 to 1 in 106, and two sampleswere bcrlabl negative.

Seven groups reported their results:

Correct False False

Material Total result positive negativeUndiluted positive 12 12 0* 0

Diluted positive 20 13 0 7

Negative 30 26 4 ..

*Because PCR can amplify b2a2 or b3a2 mRNA, false-positive results cantheoretically be obtained

There was a striking reduction in false-positive and false-negativeresults. Three of the four false positives were for negative samplesfrom batch A which included undiluted positive samples, and thesepositive samples may have cross-contaminated negative ones

because the same b2a2 product was detected in all three. Only onefalse-positive result was seen in batch B, in which only dilutepositive samples were included. False negatives were reported in sixsamples but in four of these cases the sample was at the highestdilution (1 in 106) of bcr/abl-positive cells and in each case the nextlower dilution (1 in 105) at the same centre was correctly identified.Thus false positives can be kept to a minimum (but probably not

eliminated) by adherence to standard precautions and by avoidanceof the processing of undiluted positives with unknown samples.Contributors to this study were essentially the same as those for the firstmulticentre study. Additional contributors were Dr G. Martinelli (Verona)and Dr P. Richard (Paris).

Haematology Department,Royal Postgraduate Medical School,London W12 ONN, UK

TIMOTHY HUGHES

JOHN M. GOLDMAN

1 Hughes TP, Janssen JWG, Morgan G, et al. False positive results with PCR to detectleukaemia-specific transcript. Lancet 1990; 335: 1037-38.

2 Kwok S, Higuchi R. Avoiding false positives with PCR Nature 1989, 339: 237

Iodine-induced hypothyroidism in infantstreated with continuous cyclic peritoneal

dialysisSIR,-An excessive intake of iodine can lead to hypothyroidism andgoitre.’ In adults this has no serious consequences and is easilytreatable; however, iodine intoxication in infants can cause severedamage, such as impaired psychomotor development due to

longstanding hypothyroidism, or suffocation due to a congenitalgoitre Gavin et aP reported two adults with iodine-inducedhypothyroidism associated with continuous ambulatory peritonealdialysis, apparently induced by excessive amounts of iodineresorbed from povidone-iodine-containing dialysate (although

Gardner et al4 have subsequently disagreed with this explanation),A striking feature was that serum T4 levels were only moderatelydecreased.

Peritoneal dialysis, especially continuous cyclic peritonealdialysis (CCPD), is used increasingly to treat very young infants.Although povidone-iodine is no longer used in dialysates, a

povidone-iodine-containing cap is used to seal the Tenckhoffcatheter during the day. Because young infants are at particular riskof iodine-induced hypothyroidism, since the Wolff-Chaikoff effect(ie, instantaneous inhibition of iodine organification) is not alwaysfollowed by the "escape mechanism", we monitored thyroidfunction. We have since observed two cases that justify this policy,The first patient, a 3-year-old boy, had severe nephrotic

syndrome and progressive loss of renal function due to glomerularsclerosis. A longstanding hypothyroidism due to excessive renal lossofT4 resolved when he became anuric. Nevertheless, his plasma T4level fell to 50 nmol/l, and plasma thyroid-stimulating hormoneincreased to 37 mU/1 shortly after peritoneal dialysis. Asimultaneous increase of plasma thyroglobulin to 1300 pmoljl(normal 15-375 pmol/1) suggested defective thyroid hormonesynthesis. Indeed, iodine organification seemed to be defective, asshown by a high radioiodide uptake and a 90% discharge ofradioiodide after administration of perchlorate. The second patient,an 18-month-old girl, had bilateral Wilms’ tumours, mesangialsclerosis (Drash syndrome), and features of a severe nephroticsyndrome, including a T4-wasting type of hypothyroidism. Afterbilateral nephrectomy and the start of CCPD, plasma T4 droppedrapidly to 10 nmolfl with a simultaneous rise of plasma thyroid-stimulating hormone to 2900 mU/1. The patient had high serumthyroglobulin (2300 pmol/1), a high radioiodide uptake, and 90%discharge after administration of perchlorate. In both cases theiodine source was shown to be the sealing cap of the Tenckhoffcatheter. The iodine inside this cap diffused into the catheter andflushed into the peritoneal cavity at the next dialysis session.

Department of ExperimentalPaediatric Endocrinology,

Academic Medical Centre,1105 AZ Amsterdam, Netherlands

THOMAS VULSMADARIA MENZELFILOMENA C. B. ABBADMARGARETH H. GONS

JAN J. M. DE VIJLDER

1 Morgans ME, Trotter WR. Two cases of myxoedema attributed to iodide

administration Lancet 1953; ii 1335-372 Galina MP, Avnet NL, Einhorn A. Iodides dunng pregnancy. an apparent cause of

neonatal death N Engl J Med 1962; 267: 1124-27.3 Gavin LA, Eitan NF, Cavalieri RR, Schmidt WR Hypothyroidism induced by

continuous ambulatory peritoneal diaylisis. Western J Med 1983; 138: 562-654 Gardner DF, Mars DR, Thomas RG, Bumrungsup C, Misbin RI Iodine retention

and thyroid dysfunction m patients on hemodialysis and continuous ambulatoryperitoneal dialysis. Am J Kidney Dis 1986; 7: 471-76.

Polycythaemia and HIV infection

SIR,-Dr Battan and colleagues describe a patient with AIDS andpolycythaemia (June 2, p 1342). We have seen a similar patient whohas presumed HIV disease but not AIDS.A 41-year-old homosexual man presented in September, 1988,

with malaise, fever, night sweats, haematuria, and dysuria. Hesmoked 40 cigarettes per day and consumed 25 units of alcoholweekly. Examination showed plethora, leuconychia, angularstomatitis, oral candidosis and hairy leucoplakia, generalisedlymphadenopathy, and a smooth 4 cm enlarged liver. Haemoglobin(Hb) was 20-0 g/dl, with a packed cell volume (PCV) of 062. In1979 his Hb had been 143 gdl and in 1983 it was 17-8 gfdl. Gammaglutamyltransferase and alkaline phosphate were raised at 118 and169 units per litre, respectively, but later fell to normal. Resting andpost-exercise arterial blood gases were within normal limits

(pOz = 13 kPa), and carboxyhaemoglobin was 6’ 1 %. There was amild obstructive ventilatory defect and moderate reduction in gastransfer. Repeat Hb was 21-3 g/dl, with a PCV of 0-64. Meancorpuscular volume was 109 fl, and white cell and platelet countswere normal. Bone-marrow aspiration showed early megaloblasdcchanges and normal iron stores. Serum B12 was 96 ngfl and folatewas 1-0 ug/1. (Because of his polycythaemia, treatment with Me