Self-Testing in the Periodic Paralyses Using the Cardy Potassium Ion Meter
Many, if not most, physicians do not realize that it is now possible for the patient with periodic paralysis to self-test their potassium level, just as patients with diabetes test their glucose levels. The C - 131 Cardy potassium ion meter used for self-testing of potassium levels by patients is not currently approved for medical use by the FDA, nor is it sold as a medical device, but it is very sensitive measuring device which has given excellent results to the patients in our group who have used it.
We recommend that patients take their Cardy with them when they are having a serum potassium test at the lab, and just before the lab poke, do the self-test. When the lab result comes back the Cardy meter's result has invariably been identical to the lab result. In only one reported case so far has the Cardy reading not matched, and the patient reported that the Cardy had been left in her cold car for several hours prior to the test, and had not had time to warm to room temperature before the test.
Our patients do not test their blood with the Cardy, but their saliva. This is possible because the saliva concentrations of potassium match those of blood. Here are some 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 | Mixed 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:
- Fill the mouth with saliva
- Swallow
- Fill the mouth with saliva again
- 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.
- Pick the tape off the tongue and lay it on the sensor
- After two seconds read the digital readout, making note of the position of the indicator, at 10X PPM, 100X PPM or 1000X PPM.
- Remove the tape from the sensor, turn off the meter, clean the sensor face with de-ionized water (supplied), pat dry and close the cover.
Now multiply the PPM x 0.26 to get mmol/L, since we need a mmol/L reading. See the chart to determine what a saliva mmol/L reading translates to in serum K+ mmol/L.
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 in them.
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, but once mastered it's not difficult. The solutions come with the meter, and refills may be ordered from the same suppliers who sell the meter. How to calibrate the Cardy K+ Meter.
References:
- 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
- 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.)