A standard procedure for measuring conductivity of sweat as a diagnostic test for cystic fibrosis

BRIEF

CLINICAL

LABORATORY

AND OBSERVATIONS

A standard procedure for measuring conductivity of sJveat as a diagnostic test for cystic fibrosis H. Shwachman, ~ A. Mahmoodian, L. Kopito, and K. T. Khaw :BOSTON, MASS.

I N A recent r e p o r t on the m e a s u r e m e n t of sweat conductivity as a diagnostic test for cystic fibrosis, we employed h o m e - m a d e e q u i p m e n t designed by Phillips. z, 2 Since this assembly is not readily available we thought t h a t the use of a standard, inexpensive, commercially available conductivity meter, designed specifically for our purpose, a n d a m i c r o c o n d u c t i v i t y cell of known characteristics would be useful? T h i s r e p o r t describes our experience with this conductivity m e t e r (Solu M e t e r ) a n d microcell. T h e sweat sample n e e d e d is a p p r o x i m a t e l y 20 l a m b d a (0.020 m l . ) . A r e a d i n g can be m a d e in a few seconds. T h e Solu Meter, like other resistance a n d c o n d u c t a n c e measuring devices, gives a reading relative to a specific conductivity cell a n d a t e m p e r a t u r e sensitive calibration curve.

Prior to operation, the instrument was standardized in accordance with the m a n u facturer's instructions 3 a n d c a l i b r a t e d ( T a b l e I).4 We feel t h a t each instrument a n d microcell should be calibrated with s t a n d a r d solutions. Should the microcell need replacem e n t a new standardization is desired with the new cell. T h e observations in this study were obtained over a 6 m o n t h period beginning in June, 1963. A total of 275 individuals u n d e r 17 years of age were subjected to the sweat test. T h e left f o r e a r m was used for the routine pilocarpine sweat test with q u a n t i t a t i o n of sodium, potassium, a n d chloride2 A t the same time, the right f o r e a r m was used for the conductivity determination. S u m m a r y of the conductivity d a t a is shown in T a b l e I I . This test clearly separates patients with cystic

From the Division o[ Laboratories and Research and the Department o[ Medicine, T h e Children's Hospital Medical Center, and the Department o[ Pediatrics, Harvard Medical School and The Children's Cancer Research Foundation, Boston. This investigation was supported in part by a Public Health Service Research Grant A6339 [rom the Division o[ Arthritis and Metabolic Disease Public Health Service and [rom the National Cystic Fibrosis Research Foundation. r The Children's Hospital Medical Center, 300 Longwood Avenue, Bostofi, Mass. 02115.

T a b l e I. C o n d u c t i v i t y of s t a n d a r d solutions of K C1

Standard solution

Solu Meter reading 25 ~ C.

Specific conductance (mieromhos/cm.)* Experimental

I Re[erence standard~

0.01 N 6 1,380 1,413 0.02 N 12 2,760 2,765 0.05 N 30 6,900 -0.10 N 56 12,880 12,880 0.14 N 76 17,480 -0.18 N 95 21,850 -*Mieromhos/cm. ~ Solu Meter reading X 230.

Articles submitted for this section should not exceed t,000 words and may contain 1 or 2 illustrations or tables. Bibliography should not exceed 7 re[erences.

432

Volume 66 Number 2

Brief clinical and laboratory observations

433

Table II. Sweat conductivity of 33 patients with cystic fibrosis and 242 controls age 12 days to 17 years No. of Scale reading (25 ~ Group cases Range I Mean I Cystic fibrosis 33 52-98 73 Controls 242 12-40 19 ~Micromhos/cm. z Solu Meter reading X 230.

I00-,

NQ

900 oJ

C.) S. D. +13 -+ 7

Specific conductance (micromhos/cm.)* Range

Mean

11,960 to 22,540 2,760 to 9,200

16,790 4,370

t

S. D. +2,990 -+1,610

AGE

C E PATIENT

x

55

to ITYRS

CONTROLS

*

242

1o 17YRS

8o-

X c~

70-

Z

< uJ

60-

n-

r~

50-

uJ

p"'

40-

=,

30-

-.. o

m

~-".." 9

--'2" 2":2".'r

20-

. . . . . . . .

.

Micromhos = Solu Meter Reading X 2 3 0

.o

I0-

o 6

2'o 3'O 4b ~'o go zb 8b 9'o 16o lio I~o i+o 14o i~o i~o #o l~o SODIUM

Meq/L

Fig. 1. Studies in diagnosis of cystic fibrosis comparison of conductivity versus sweat sodium (mEq./L.)

I0090-

No

AGE

35

to ITYRS~

" 242

to 17 YRS.

CE PATIENTS

x

CONTROLS

1

P IZ')

80Z ~ 1i

o4 (.9 Z Q

70" 60-

I.d

n," n-

LIJ FLU

5040-

=E

9 .~

50-

..... ~ ,,~~

--I 0

03

~

-

Micromhos

= Solu Meter Reading X

230

....

20" I0-

0

ib 2b 3'o 4b 60 go 7b 8'O 40 Ibo iio iko i~o t,io I~o I~o iko i~o CHLORI DE ( M e q / L ;

Fig. 2. Studies in diagnosis of cystic fibrosis comparison versus sweat chloride ( m E q . / L . ) .

4 34

February 1965

Brief clinical and laboratory observations

fibrosis from the large group of patients who served as controls. A comparison of the sweat sodium concentration is m a d e with the Solu M e t e r readings a n d is illustrated in Fig. 1. Sweat chloride concentrations were equally well related to the Solu M e t e r readings (Fig.

cystic fibrosis ranged from 48 to 78 with a mean value of 59. The highest reading in the control group was 35. A new micro conductivity cell was used in these measurements.

2).

1. Phillips, W. R.: Electrical conductivity of sweat: A simple home-assembled apparatus, Pediatrics 32: 89, 1963. 2. Shwachman, H., Dunham, R., and Phillips, W. R.: Electrical conductivity of sweat: A simple diagnostic test in children, Pediatrics 32: 85, 1963. 3. Industrial Instruments Inc., 89 Commerce Road, Cedar Grove, N. J. 4. Conductivity of standard solutions, in Handbook of chemistry and physics, ed. 44, Cleveland, 1963, Chemical Rubber Publishing Co., p. 2691. 5. Shwachman, H., and Antonowicz, I.: The sweat test in cystic fibrosis, Ann. New York Acad. Sc. 93: 600, 1962.

O n e d i s a d v a n t a g e of the p r o c e d u r e for d e t e r m i n i n g conductivity is our failure to o b t a i n an a d e q u a t e sample of sweat from some patients. A total of a p p r o x i m a t e l y 5 p e r cent failures were noted as contrasted to a failure of a b o u t 3 p e r cent by the collection of sweat onto a p a d a n d quantification. Addendum. Since this we have performed tests tients with cystic fibrosis, The conductivity reading

paper was submitted on 75 additional paarid on 996 controls. in the patients with

REFERENCES

The rubella syndrome Joan P. Giles, M.D., "~Louis Z. Cooper, M.D., and Saul Krugman, M.D, NEW YORK, N. Y. T H E nationwide epidemic of rubella which occurred in 1964 m a y be recorded as one of the largest in the history of the U n i t e d States. T h e serious consequences of rubella in p r e g n a n c y have been well d o c u m e n t e d . 1-3 I n f e c t i o n d u r i n g the first t r i m e s t e r of pregn a n c y m a y be followed b y the rubella synd r o m e which includes cataracts, deafness,

From the Departments of Pediatrics and Medicine, New York University School of Medicine, and the Willowbroo.k State School, Staten Island, N. Y. This investigation was carried out under the sponsorship of the Commission on Viral Infections, Armed Forces Epidemiological Board, and was supported in part by the Office of the Surgeon General, U. S. Army Medical Research and Development Command; in part by Public Health Service Research Grant No. A I 04335-03, from the National Institute o~ Allergy and Infectious Diseases; and in part by the Health Research Council of the City of New York under Contract No. 1-304. See also "'The teratogenicity of maternal rubella," p. 380. aNew York C~ty Health Research Coundl Awardee.

congenital h e a r t disease, m i c r o c e p h a l y , a n d m e n t a l r e t a r d a t i o n . These anomalies m a y occur singly or in combination. T h e toll of the 1964 e p i d e m i c will be d e t e r m i n e d after the b i r t h of m a n y p o t e n t i a l l y affected babies early in 1965. T h e purpose of this brief r e p o r t is twofold: (1) to review the clinical manifestations in 20 children born following a history of rubella d u r i n g the first trimester of pregnancy; a n d (2) to record the d e l a y in recognizing the various m a l f o r m a t i o n s at birth. T h e clinical manifestations of the rubella syndrome in 20 children, 3 to 15 years of age, are shown in T a b l e I. T h e chronology of the recognition of the various anomalies is listed in T a b l e I I . I n f a n t a t birth. A m o n g the 20 c h i l d r e n there were 12 who were b o r n at full t e r m a n d 8 who were p r e m a t u r e at birth. E i g h t y per cent of the total group, w h e t h e r prem a t u r e or full term, h a d b i r t h weights u n d e r 5 pounds, 11 ounces. T h e a v e r a g e b i r t h