POTASSIUM PROCEDURE

Intended for the Quantitative Determination of Potassium in Serum Using a Turbidimetric Method

SUMMARY AND EXPLANATION

Potassium is a major intracellular cation that is an essential component of all living matter. The role of potassium in the human body is great as there is almost no metabolic function that is not dependent on or affected by potassium concentrations. Important functions of potassium are maintenance of osmatic pressure, proper pH, heart and muscle  function and electron transfer reactions. Disturbance of the potassium balance has serious consequences. Decreassed is characterized by muscle weakness, irritability, paralysis, fast heart rate and eventual cardiac arrest. Abnormally high levels produce symptoms of mental confusion, weakness, numbness, slow heart rate and eventually vascular collapse and cardiac arrest.

PRINCIPLE

Potassium ions react with sodium tetraphenyboron to produce a finely dispersed suspension of potassium tetraphenylboron. A stablizing and dispersing agent has been added. The absorbance at 535 nm is directly proproportional to potassium concentration.

REAGENTS: FOR IN-VITRO DIAGNOSTIC USE

POTASSIUM REAGENT - (Cat. No. 3101)

REACTIVE INGREDIENTS:

6% Sodium Tetraphenylboron, Stabilizing and dispersing agents present.

PRECAUTIONS:

Avoid contact with skin, eyes and clothing. In case of contact, wash with large amounts of water. Do not take internally.

STORAGE AND STABILITY:

Store at 15-30ºC. Stable until expiration dat if vials remain sealed and unopened. DO NOT EXPOSE TO COLD TEMPERATURES. Reagent will precipitate and not resolubilize.

DETERIORATION:

Reagent should be clear and colorless. Turbidity of the reagent indicates deterioration.

POTASSIUM CALIBRATOR - (Cat. No. 3102)

REACTIVE INGREDIENT:

Potassium chloride equivalent to 4.0 mEq/L serum potassium.

PRECAUTIONS:

Causes irritation. Avoid contact with skin, eyes and clothing. In case of contact, whash with water.

STORAGE AND STABILITY:

Store at 15-30ºC. Stable until expiration date on bottle if sealed tightly.

DETERIORATION:

The calibrator should be clear and colorless. Turbidity indicates deterioration.

Use a spectrophotomer or colorimeter calibrated at 530-540 nm.

SPECIMEN COLLECTION

PRECAUTIONS:

1. Use unhemolyzed serum or plasma. Hemolyzed samples may not be used due to contamination with extracellular potassium.

2. Separate serum from clot as soon as possible.

3. Avoid microbial contamination.

4. Potassium containing anticoagulants must not be used.

SAMPLE STORAGE:

Samples may be stored at 2-8ºC for one week.

INTERFERING SUBSTANCES:

Young et al. have reviewed drug effects on serum potassium. As stated, hemolysis must be avoided.

PROCEDURE

MATERIALS PROVIDED:

POTASSIUM REAGENT (Cat. No. 3101) and POTASSIUM CALIBRATOR (Cat. No. 3102) provided as POTASSIUM REAGENT SET (Cat. No. 3100-2).

MATERIALS REQUIRED BUT NOT PROVIDED:

1. 0.05 mL micropipettor.

2. 2.25mL Pipettor or dispenser.

REACTION CONDITIONS:

Wavelength 535nm

Incubation Time 1 minute

Incubation Temperature Ambient

Sample Volume 0.05 mL

Reagent Volume 2.5 mL

PROCEDURE:

1. Label a series of vials REAGENT BLANK, CALIBRATOR, CONTROL, SAMPLE 1, etc.

2. Dispense 2.5 mL Potassium Reagent into tubes.

3. Add 0.05 mL if CAKUBRATIR "QUICKLY" into vial labeled CALIBRATOR. Cap the tube and vigorously mix the tube by inversion.

4. Repeat this process for each CONTROL and PATIENT SAMPLE. Add nothing to the vial labeled BLANK.

5. Let all vials stand at ambient temperature for at least one (1) minute.

6. Insert BLANK vial into instrument read well and set to zero absorbance.

7. Insert CALIBRATOR vial into instrument read well and read absorbance. If a direct concentration readout is available, set value of calibrator to equal 4.0 mEq/L.

8. Read absorbance/concentration of unknowns.

NOTE: The reacted CALIBRATOR  vial may be retained and reused for twenty-four (24) hours. Gently invert at least four (4) times before using to calibrate the instrument.

STABILITY OF FINAL REACTION PRODUCT:

The final reaction product is stable for at least 24 hours.

CALIBRATION:

EAGLE recommends the use of the EAGLE POTASSIUM CALIBRATOR supplied with the reagent set. The procedure exhibits linearity between 2.0-8.0 mEq/L. Samples greater than 8.0 mEq/L should be diluted with deionized water 1:1, assay repeated and results multiplied by two (2).

QUALITY CONTROL:

The reliability of test results should be monitored routinely using suitable normal and abnormal quality control materials analyzed in the same manner as the unknowns. Values should approximate those obtained with flame photometry.

CALCULATION OF RESULTS

The following equation is used to determine unknown concentrations when direct readout is not used

Unknown Conc. =

Unk. Abs.

---------------  X  Std. Conc. (mEg/L)

Std. Abs.

EXAMPLE:

A 4.0 mEg/L calibrator had abs. =  0.602 whuile the unknown had abs. = 0.512. The potassium concentration of the unknown is:

0.512  

--------- X  4.0 mEq/L   = 3.4 mEq/L

0.602

LIMITATIONS

Contaminated glassware is greatest source of error. Lipemic and hemolyzed serum can not be used. Exteernal contamination with ammonia, calcium and magnesium must be avoided. Use only pure deionized water for diluting elevated samples.

EXPECTED VALUES

SERUM 3.6 -5.5 mEq/L

PLASMA 4.0 - 5.8 mEq/L

The range represents the 95% confidence interval for 25 samples obtained from clinically normal population. EAGLE recommends that each laboratory establish its own range of expected values.

PERFORMANCE CHARACTERISTICS

PRECISION:

Normal and abnormal control sera were assayed 20 times each to establish within run precision and for 10 working days to establish run to run

MEAN / ST.DEV. / %CV

WITHIN RUN   

Normal 3.5 / 0.06 / 1.7

Abnormal 6.1 / 0.15 / 2.5

RUN TO RUN  

Normal 3.5 / 0.12 / 2.4

Abnormal 6.1 / 0.22 / 3.1

SPECIFICITY:

A comparison of the EAGLE POTASSIUM PROCEDURE with another commercially available turbidimetric method showed a correlation of 99% with 35 serum samples in the normal and abnormal range. A comparison with the flame photometer method showed a correlation of 95% with the same 35 samples.

SENSITIVITY:

The EAGLE POTASSIUM PROCEDURE  has sensitivity of 0.007 mEq/L per0.001 absorbance unit.

REFERENCES

1. Tietz, N.W., Textbook of Clinical Chemistry, W.B. Saunders Co., Philadelphia, 1986,  p. 1172-1175.

2. Sunderman, F.W. Jr., Sunderman, F.W., Am. Hjourn. of Clin. Pathology, vol. 29, p. 95, 1958.

3. Young, D.S., Pestaner, L.c. and Gibberman, V., Clin. chem. 21, 371d (1975).