Testing for Sodium and
Potassium in Blood, Urine or Hair
1. Sodium and Potassium in Blood
Sodium and potassium are necessary to maintain water balance in the
body for proper functioning of the nerves, blood pressure regulation,
aiding absorption of major nutrients, regulation of acid-base balance
and contraction of the muscles, in addition to other cellular chemical
reactions.(1)
ELECTROLYTE DISTRIBUTION
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Electrolyte
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Extracellular meq/liter
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Intracellular meq/liter
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Function
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Sodium
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142
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10
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fluid balance, osmotic pressure
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Potassium
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5
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100
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Neuromuscular excitability acid-base balance
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Extracellular and Intracellular Fluids
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Sodium and
potassium concentrations in extra- and intracellular fluids are nearly
opposites. This reflects the activity of cellular ATP-dependent
sodium-potassium pumps. Potassium levels are mainly controlled by the
hormone aldosterone. Potassium levels often change with sodium levels.
When sodium levels go up, potassium levels go down, and when sodium
levels go down, potassium levels go up.(2) |
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Electrolytes determine the chemical and physical reactions of
fluids |
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Ion fluxes are restricted and move selectively by active
transport |
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Nutrients,
respiratory gases, and wastes move unidirectionally |
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Osmolalities of all body fluids are equal; changes in solute
concentrations are quickly followed by osmotic changes |
Because Sodium is a major
element in extracellular fluid, it is preferably tested in serum.
Blood Potassium levels can be falsely elevated by a variety of
circumstances surrounding specimen collection and specimen processing.
For example, if a patient is clenching and relaxing his fist, the
potassium level in his blood may increase. If blood samples are
delayed in getting to the lab or if the blood tubes are subjected to
vigorous shaking or rough handling in transit, potassium may leak from
red blood cells and falsely elevate the potassium in the serum.
Other Factors affecting Potassium Levels in blood
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Taking potassium supplements. |
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Taking medicines, such as antibiotics that contain potassium (such as benzylpenicillin, also called penicillin g, also
called benzylpenicillin, nonsteroidal anti-inflammatory drugs
(NSAIDs), heparin, insulin, glucose, corticosteroids,
diuretics, medicines used to treat high blood pressure and
heart disease, and natural licorice (Glycyrrhiza glabra). |
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Overuse of laxatives. |
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Severe vomiting. |
Potassium measurement in whole-blood specimens may convenient.
However, the presence of hemolysis in whole-blood samples cannot be
determined by present analytical systems. There is a risk of reporting
misleadingly increased whole-blood potassium concentrations for
unrecognized hemolyzed samples, with potential for subsequent patient
misdiagnosis and mistreatment.(3) Consequently, potassium is best tested
in serum.
2. Sodium and
Potassium in Urine
Sodium:
Measurement of the urine sodium concentration is vital in determining
the integrity of tubular reabsorptive function. Low urine sodium
concentration thus indicates not only intact reabsorptive function but
also the presence of a stimulus to conserve sodium, whereas a high
urine sodium concentration may signify other salt wasting etiologies.
It is usually ordered when we need to distinguish between various
forms of renal failure and classifying hyponatremia.(4)
Sodium
urine excretion fluctuates depending on the sodium intake. Conditions
associated with increased urine sodium include the following:(5)
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Excessive dietary salt |
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Diuretic therapy |
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Adrenal insufficiency |
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Salt-wasting nephropathy |
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Acute tubular necrosis |
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Analgesic abuse-induced interstitial nephritis |
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Syndrome of inappropriate antidiuretic hormone hypersecretion
(SIADH) |
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Vomiting |
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Hypothyroidism |
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Postobstructive diuresis |
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Hepatic failure |
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Congestive heart failure |
The reference range for urine sodium is 40-220 mEq/L/24 hours.
Potassium: Measurement of the urine potassium
concentration can be done on a 24hr urine sample or a random sample.
The usual range for a person on a regular diet is 25 to 125
milliequivalents per liter per day. However, lower or higher urinary
levels may occur depending on the amount of dietary potassium.
High
urine potassium levels may be due to:
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Acute tubular necrosis |
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Cushing syndrome (rare) |
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Diabetic acidosis and other forms of metabolic acidosis |
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Eating disorders (anorexia, bulimia) |
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Low blood magnesium levels (hypomagnesemia) |
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Hyperaldosteronism (very rare) |
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Renal tubular acidosis |
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Use of non-potassium-sparing diuretics |
Low urine potassium levels may
be due to:
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Adrenal gland insufficiency |
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Hypoaldosteronism |
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Certain medications, including beta blockers, lithium,
trimethoprim, potassium-sparing diuretics, or nonsteroidal
anti-inflammatory drugs (NSAIDs) |
Chelation Therapy does not affect potassium. Hence there is no
need to include potassium in urine provocation test profiles. 3. Sodium and Potassium
in Hair
We do not routinely test sodium or
potassium in hair. Our internal studies indicate that sodium and
potassium levels of unwashed hair are naturally elevated through
sweat, cosmetics or other external factors. Hence, the analysis of
unwashed hair samples results in false high sodium values.
With
the following experiment, we took a mix of homogenized hair samples
and repeatedly tested sodium and potassium prior to washing. We took
part of this batch of unwashed homogenized hair, washed and tested
them repeatedly until we came to a final sodium and potassium value.
As the data indicates, not washing hair will provide falsely elevated
results.
![Na+K in hair before and after washing samples](http://www.microtraceminerals.com/fileadmin/uploads/pics/en/newsletter/Na_K_hair_before_and_after_washing.jpg)
Our internal studies indicate that several washing procedures with
de-ionized solutions are needed to remove external contaminants such
as sodium and potassium. Although Wilson reports that ‘the adrenals
and kidneys regulate the hair sodium level’, we could find no
evidence. The laboratory he refers to does not wash hair samples prior
to testing i.e. external contaminants are not removed.
While a
recent Pakistani study found significantly lower levels of Ca, Mg, and
K in the biological samples (blood, serum, and scalp hair) of male and
female rheumatoid arthritis patients when compared to referents of
both genders,(6) we see no advantage of testing sodium and potassium in
hair rather than serum.
A US laboratory performing Sodium and
Potassium analysis in hair states that “Hair measurement should be
considered a screening test only; blood testing for Na and electrolyte
levels is much more diagnostic and indicative of status.”(7)
When
symptoms such as weakness, tiredness, tingling or numbness, nausea or
vomiting, abdominal cramping, bloating, constipation or irregular
heart beat suggest low potassium, screening in hair only delays proper
diagnosis, especially since a quick check for electrolytes in blood
makes diagnostic sense.
Hyponatremia is rare, possibly linked
to excessive use of diuretics, diarrhea, drinking excess water, or is
a result of a disorder in the body’s regulation of sodium or water. To
diagnose the sodium status, blood diagnosis is a must, possibly
including aldosterone or vasopressin levels.
In lieu of all
this information, sodium or potassium in hair is not part of our hair
profiles.
We wish you all the
best. If you find this newsletter informative, let us know.
E.Blaurock-Busch and team References:
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1) |
Shorecki K, Ausiello D. Disorders of sodium and water homeostasis. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 118.
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2) |
http://www.webmd.com/a-to-z-guides/potassium-k-in-blood
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3) |
Hawkins R. Measurement of Whole-Blood Potassium
- Is It Clinically Safe? Clinical Chemistry. Dec 2003 vol. 49 no. 12 2105-2106
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4) |
http://emedicine.medscape.com/article/2088449-overview
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5) |
http://www.nlm.nih.gov/medlineplus/ency/article/003599.htm |
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6) |
Afridi HI et al. Evaluation of calcium, magnesium, potassium, and sodium in biological samples (scalp hair, serum, blood, and urine) of Pakistani referents and arthritis patients of different age groups. Clin Lab 2012;58(1-2):7-18
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7) |
http://www.doctorsdata.com/repository.asp?id=1270 |
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