Ion system

Clin. Biochem. 10, (1) 44-46 (1977)

Clinical Evaluation of the Technicon Stat/Ion System DAVID SLAUNWHITE, Ph.D., JAMES C. CLEMENTS, B.S, and GUSTAVO REYNOSO, M.D. Department of Pathology, Wilson Memorial Hospital, Johnson City, New York 13790, USA (Accepted September 26, 1976)

CLBIA, 10, (1) 44-46 (1977) Cli~. Bioche~n. Slaunwhite, D., Clements, J. C., and Reynoso, G.

Department o.f Pathology, Wilson Memorial Hospital, Johnson City, N Y 13790, USA CLINICAL E V A L U A T I O N OF T H E TECHNICON S T A T / I O N SYSTEM 1. We describe our evaluation of the Technicon Star/Ion, an i n s t r u m e n t which performs sodium, chloride and bicarbonate analysis simultaneously. 2. All four of the assays resulted in linear response over the entire clinical range with insignificant carryover between specimens. 3. Precision studies for within-run variation were: sodium 0.3%, potassium 0.7%, chloride 0.5% and bicarbonate 1.6%. Day-to-day precision was similar to the within-run precision. 4. Comparison methods for sodium, potassium, chloride and bicarbonate utilizing flame photometry, chloridometry and titration of released carbon dioxide respectively showed the following linear regression and correlation coefficients: sodium y : 0.96 + 5.5 (a -----0.988) potassium y = 1.01x + 0.0 (a -- .996) chloride y -- 0.99x + 1.0 (a ----.993) bicarbonate y _-- 1.0x -{- 1.2 (a = .969).

THE TECHNICON

STAT/ION SYSTEM is an integrated, dual-module instrument capable of simultaneously analyzing sodium, potassium, chloride and bicarbonate. "~ Approximately 300 ul of sample is required to perform the analysis of the four constituents at the nonvariable rate of 48 samples per hour. Sodium, potassium and chloride specific ion electrodes used in this system are referenced to a fourth c o m m o n electrode. The key element in each electrode is the presence of a m e m b r a n e which can selectively monitor the activity of a particular ion in solution. Glass, valinomycin and silver chloride are the membranes respectively utilized to measure the sodium, potassium and chloride ions. Inside the electrode the m e m b r a n e is in contact with an inner electrolyte which subsequently is in contact with an inner electrode. W h e n the electrode is submerged in the solution to be assayed, a voltage differential is developed across the m e m b r a n e which, as defined in the Nernst equation/e~ is a function of the activity of the ion selectively monitored by the membrane.

Correspondence: David Slaunwhite, Ph.D., Department of Pathology, Wilson Memorial Hospital, Johnson City, NY 13790, USA

In the b i c a r b o n a t e a s s a y 100 ul of s e r u m is added to a k n o w n q u a n t i t y of acid a n d mixed v i g o r o u s l y while a i r is forced t h r o u g h the solution. E l e c t r i c a l l y g e n e r a t e d h y d r o x y l a n i o n s are used to b a c k - t i t r a t e the solution to a pH of 7.55 which is m o n i t o r e d by dual w a v e l e n g t h optics u s i n g an acid-base i n d i c a t o r . T h e a m o u n t of b i c a r b o n a t e is i n v e r s e l y p r o p o r t i o n a l to the a m o u n t of c u r r e n t utilized. Since this procedure only m o n i t o r s b i c a r b o n a t e a n d not total CO2, it is n o t affected by the loss of c a r b o n dioxide in the sample.

METHODS AND MATERIALS

Instrument and Controls A Technicon S t a t / I o n (serial #PV50302) was purchased from the Technicon Corporation, Tarrytown, New York 10591. We utilized only reagents purchased from Technicon. Lyophilized normal and abnormal Hyland Control sera (Hyland Laboratories, Inc. Costa Mesa, California 92626) were used.

Stat/Ion Reagents The internal ( S t a t / I o n Calibration Standard, sodium 140 meq/L, potassium 5 meq/L, chloride 105 meq/L, T030592) and external ( S t a t / I o n Buffered Linearity Reference with bicarbonate, sodium 160 meq/L, potassium 8.0 meq/L, chloride 120 meq/L, bicarbonate 25.0 meq/L, T030672) calibration standards were utilized as received. The S t a t / I o n bicarbonate color reagent (T010660) requires three drops of S t a t / I o n s u r f a c t a n t (T210591) added daily and mixed thoroughly. Approximately 4.5 ml of reagent is used per sample. One bottle of S t a t / I o n diluent stock (T210590) is diluted to 4000 ml with distilled water, three drops of s u r f a c t a n t added, and the solution t h o r o ~ h l y mixed. Approximately 6 ml of diluent is used per sample.

Comparison Methods The Instrumentation Laboratories, Inc. Flame Photometer 343 (Watertown, Mass. 02172, serial #001631) was used to compare the sodium and potassium values. All reagents utilized with this i n s t r u m e n t were purchased from I. L. A Corning Chloride Meter (Corning Scientific Instruments, Medfield, Mass. 02052, serial #AA358) was used to compare the chloride values. All reagents and parts used with this i n s t r u m e n t were purchased from Corning. A single channel Technicon Autoanalyzer was used to compare the bicarbonate values/2~ We utilized 10, 20, 25, 30 and 40 meq/L standards assayed at a rate of 60 samples per hour. Since the Total CO~ value, as measured on the Autoanalyzer, equals (HCO.~ + H2CO.~) and the average carbonic acid value is 1.05 to 1.45 meq/L, the value obtained by the S t a t / I o n should be approximately 1.2 meq/L lower.

Procedure The standards, controls and samples were poured into labelled autoanalyzer cups and placed on the sample tray.

E V A L U A T I O N OF T E C H N I C O N S T A T / I O N S Y S T E M A minimum of four calibration standards are required with each run followed by a serum primer. The results of the four assays are then printed out simultaneously. RESULTS Linearity. J The linear studies of each compound are p e r f o r m e d using serial dilutions of a spiked

s a m p l e ( T a b l e I) . A l t h o u g h t h e e l e c t r o d e s d i v e r g e f r o m l i n e a r i t y at u n u s u a l l y h i g h a n d low s e r u m v a l u e s , t h i s g e n e r a l l y does n o t c r e a t e a n y p r o b l e m s within the restricted clinical ranges. Carryover and/or Electrode Responsivity. -- The c a r r y o v e r on t h i s i n s t r u m e n t s h o u l d be m i n i m a l as 4.5 ml o f d i l u e n t is f l u s h e d t h r o u g h t h e s a m p l e p r o b e a f t e r s a m p l i n g . In t h i s s t u d y t h e c r i t i c a l p o i n t is t h e a b i l i t y of t h e e l e c t r o d e s to r e s p o n d p r o p e r l y a f t e r e x p o s u r e to an e l e v a t e d s a m p l e . T h r e e s p i k e d s a m p l e s f o l l o w e d by t h r e e n o r m a l s e r a , o f w h i c h t h e a v e r a g e o f t h e l a t t e r t w o v a l u e s is s u b t r a c t e d f r o m t he f i r s t , w e r e u s e d to e v a l u a t e t h e s u m o f t h e c a r ryover and electrode responsiveness; sodium 1 m e q / L p o t a s s i u m 0.4 m e q / L , c h l o r i d e 0.6 m e q / L , b i c a r b o n a t e 0.8 m e q / L . R e s p o n s i v i t y of t h e elect r o d e s a p p e a r s e x c e l l e n t w h i l e t h e c a r r y o v e r is minimal.

Precision

45

Studies

The within-run precision was excellent at both normal and abnormal levels (Table II). Day-to-day p r e c i s i o n w a s s l i g h t l y p o o r e r f o r all f o u r c o n s t i t u e n t s a t b o t h l e v e l s b u t w i t h i n a c c e p t a b l e l i mi t s . Correlation

Studies

T h e c o r r e l a t i o n d a t a a r e p r e s e n t e d in T a b l e III. A l t h o u g h t h e y - i n t e r c e p t (b) an d sl o p e (m) a r e c o m m o n l y u t i l i z e d p a r a m e t e r s to e v a l u a t e c o n s t a n t an d r a n d o m e r r o r , t h e y a r e d e p e n d e n t on t h e r a n g e o f v a l u e s a s s a y e d . '3'

DISCUSSION In t h i s s t u d y t h e d a t a o b t a i n e d f o r t h e s o d i u m correlation possibly reflects the limited clinical r a n g e assayed. A l t h o u g h t h e r an d o m , c o n s t a n t a nd proportional errors are acceptable, the correlation c o e f f i c i e n t f o r t h e b i c a r b o n a t e d e t e r m i n a t i o n is l ow due to t h e c o m p a r i s o n o f b i c a r b o n a t e v a l u e s w i t h t o t a l CO~. v a l u e s o b t a i n e d on t h e T e c h n i c o n A u t o Analyzer.

TABLE 1 PRECISION STUDIES FOR THE TECHNIC.ON STAT/ION SODIUM N ................................ ~, within run . . . . . . . . . . . . . . . . . . . . . . CV, within run . . . . . . . . . . . . . . . . . . . . . ~, day to day . . . . . . . . . . . . . . . . . . . . . . . CV, day to day . . . . . . . . . . . . . . . . . . . . .

1{30 141 0.3 141 0.6

POTASSIUM

100 154 0.5 154 0.7

100 4.6 1.0 4.3 1.7

100 7.7 0.7 7.7 1.0

I

CHLORIDE 100 103 0.4 103 1.0

[ BICARBONATE

100 123 0.5 123 1.2

i

100 12 3.6 14 4.9

i

100 20 1.6 20.7 2.6

1 i

TABLE 2 LINEARITY OF THE TECHNICON STAT/ION

SODIUM Theory 7O 90 110 120 140 160 180 SloFe b r Sy/x

POTASSIUM Stat/Ion

Theory

73 92 112 121 140 158 176

~

CHLORIDE

BICARBONATE

Stat/Ion

Theory

Stat/Ion

Theory

2.1

5O 100 125 150 2G0

5O 100 126 152 2O3

10 20 30 40 50

2 4 6.0 8 10

4.1

6.0 7.9 9.7

Stat/lon 8.3 19.4 29.5 40 50.4

L i

0.93 8.80 0.999 0.76

: !

1.02

0.95 0.23 0.999 0.73

1.02 - 1.28

- 1.60

0.999 0.78

0.999 0.49

L

All values are the average of six determinations. TABLE 3 CORRELATION STUDIES UTILIZING THE TECHNICON STAT/ION SODIUM N ..................................

Slol~e. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . b ................................... Sy/x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

, ,

r ....................................

I

range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Max. Diff. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

j

!

100 0.96 5.5 1.36 0.9~ 120-171 +2

POTASSIUM 100 1.01 0.0 0.10 0.996 2.0-8.1 +0.2

CHLORIDE 100 0.99 1.0 1.98 0.993 73-123 +3

BICARBONATE 50 1.00 -1.2 0.81 .969 10-41 +2.5

46

SLAUNWHITE, CLEMENTS AND REYNOSO

Initially we experienced difficulty with the bicarbonate channel until we "learned" the machine and were able to establish proper preventive maintenance schedules. As recently noted by L u s t g a r t e n et al '4~, Technicon has been negligent in preparing preventive maintenance schedules, trouble-shooting manuals and training programs for this instrument. Although we had several mechanical and electronic failures, we have experienced only 48 hours of down time in one year of operation while we completed the analysis in approximately 22,000 electrolyte profiles. During this period of time only one chloride and five sodium electrodes required replacement. The potassium electrode has not required replacing d u r i n g the same time. Utilizing the anion gap [Na + K - (C1 + CO~) ] = 16 as p a r t of our quality program, we found 75% of the patients were within 16 -- 2 m e q / L while 90% were mithin 16---+4 meq/L. This agrees with the findings recently published by Witte et al c~.

Overall, the Technicon S t a t / I o n has p e r f o r m e d according to specifications in heavy 24-hour-a-day usage and appears to be a reasonable alternative to the separate determinations of chloride, bicarbonate and sodium/potassium. RE~"ERE N CES 1.

2. 3. 4. 5. 6.

Technicon Publication No. UA4-0301-10. Jan. 1976, Technicon Instruments Corp., Tarrytown, N.Y. Method N-19A, Teehnicon Instruments Cor., Tarrytown, N. Y. Westgard, J. O., and Hunt, M. R. Clan. Chem. 19, 49 (1973). Lustgarten, J. A. et al. Clin. Chem. 22, 374 (1976). Witte, D. L., Rodgers, J. T. Barrett, D. A. Clin. Chem. 22, 643 (1976). Daniels, F., Alberny, R. A.: Physical Chemistry, 3rd Ed. Wiley and Sons, New York (1966).