Testing Potassium Levels with the Cardy Potassium Ion Meter

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It is now possible for the patient with periodic paralysis to test their potassium level at home, just as patients with diabetes test their glucose levels. The LAQUA potassium ion meter is not currently approved for medical use by the FDA, nor is it sold as a medical device, but it is the new and improved version of the Cardy C-131 Potassium Ion Meter, which was a very sensitive measuring device which has given excellent results to many patients in our group who have used it. Patients do not test their blood with these meters, but their saliva. This is possible because the saliva concentrations of potassium match those of blood. 

In Jan 2013 Horiba introduced a new potassium ion meter which is much easier to use, and does not require the rigourous calibration process so many patients found difficult in the C-131. If you are buying a new potassium meter you should definitely buy the new model: Horiba LAQUA Twin Potassium K+ Compact Ion Meter (B-731).

Another helpful feature is that you can choose the readout to display in mmol, which eliminates the need to do the maths conversion of ppm to mmol required when you use the C-131.  One listed use is for the LAQUA is measuring potassium in "animal" bodily fluids such as urine and saliva. This does not mean it is an FDA approved device meant for medical use, but NASA uses Horiba meters to test the water reclaimed from sewage and reused as drinking water for astronauts at the International Space Station. 

The LAQUA is more expensive, currently selling for $349.00 USD as opposed to the C-131 at $249.00. 

We do not sell these meters or receive any financial compensation from talking about using them. To find out where to buy one put the meter's name in your browser window and seek out a dealer in your country.

For those who still own or use the C-131, the directions are below.

For a printable chart in pdf format click here.  There's also an on-line calculator which will do the math for you here. 

Here are some medical journal references:

Although a variety of components is always present in saliva, the total concentration of inorganic and organic constituents is generally low when compared to serum. The fraction of saliva represented by water usually exceeds 0.99.

Of the inorganic constituents, sodium and potassium (and perhaps calcium) are the cations of major osmotic importance in saliva; the major osmotically active anions are chloride and bicarbonate...The concentration of potassium, calcium, urea, uric acid, and aldosterone are highly correlated to those existing in plasma. 1

Electrolyte concentrations [in saliva] are comparable to serum values 2

Parameter ---     Saliva ---------    Plasma

Potassium  ---- 8-40 mmol/L ----- 3.5-5.5 mmol/L

The subject must not have eaten, brushed their teeth or drunk anything within 20 minutes prior to testing.

To do the test:

Begin with a calibrated meter which has been turned on:

1. Fill the mouth with saliva

2. Swallow

3. Fill the mouth with saliva again

4. Using the plastic tweezers supplied with the unit, lay a 1/2 inch strip of test tape (supplied) on the tongue and saturate it with saliva.

5. Pick the tape off the tongue and lay it on the sensor

6. After two seconds read the digital readout, making note of the position of the indicator, at 1X PPM, 10X PPM or 100X PPM.

7. Remove the tape from the sensor, turn off the meter, clean the sensor face with de-ionized water (supplied) or with distilled water, pat dry and close the cover.

Now multiply the result in PPM x 0.026 to get mmol/L, since we need a mmol/L reading. OR put the reading from the meter (your 1 x PPM, 10 x PPM etc)  into the online calculator here and hit your enter (or return) key. 

When it's possible to do a painless two-second test and determine that one's potassium level is too high (or too low) the patient gains the ability to manage their own care far more effectively. They can document exactly how potassium levels respond to diet, activity, and other potential triggers and make adjustments which minimize weakness and paralytic attacks.

Patients can also determine, during weakness, what steps to take to normalize potassium levels, and when it is time to seek medical help. Patients can also establish a baseline at which they feel well and determine exactly how much of a shift it takes to trigger symptoms.

What are the benefits of self-monitoring potassium levels in Periodic Paralysis?

• Detection of shifts in potassium level.
• Identification of factors which cause potassium shifts
• Adjusting life-style or diet to avoid triggering shifts in potassium.
• Maintenance of potassium level within the desired range.
• Minimize weakness and paralytic attacks.

The C 131 - Cardy Potassium Ion Meter

Horiba Cardy K+ Ion Meter with calibration solutions, de-ionized water, test strip, tweezers and scissors

With the C-131 Potassium Ion Meter, you measure the potassium ion concentration by placing a small sample on the meter's flat sensor. Accurate measurements can be taken using a sample as small as a couple of drops. The meter employs a highly selective flat ion electrode. Since the electrode is unreceptive to other ions, it takes highly accurate measurements of potassium ion concentrations. The results are displayed on a digital readout. The meter is about the size of a credit card and weighs little more than an ounce, so it easily fits in a pocket or purse.

The meter requires calibration, basically a cleaning and tuning process which takes about five to ten minutes once a month, then a minute or two before use. This involves washing the sensor with special solutions and turning some dials. It's fiddly, and for anyone with poor eyesight or lack of fine motor skills it can be a challenge, but once mastered it's not difficult. Instructions for calibration are here.

The solutions come with the meter, and refills may be ordered from the same suppliers who sell the meter. We do not sell this meter. Google Cardy c-131 potassium meter and find a supplier in your area or country. Suppliers are sometimes reluctant to sell it to be used for saliva testing, even though saliva testing is pictured in the Cardy brochure. So it is best to not mention why you want it. 

1. Saliva Composition And Exercise, Josè L. Chicharro, M.D. Ph.D. Unidad de Investigacion, Escuela de Medicina Deportiva, Facultad de Medicina, Universidad Complutense de Madrid
2. International Journal of Drug Testing; Saliva as an Analytical Tool in Toxicology; Karin M. Höld, B.S.; Douwe de Boer, Ph.D.; Jan Zuidema, Ph.D.; Robert A.A. Maes, Ph.D.)