17/03/2018
HYPERKALEMIA
Definitions: Potassium levels above the normal range.
INTRODUCTION
This is a dangerous medical condition that may cause severe cardiac electrophysiology alterations, such as cardiac arrhythmias, and sudden death. All medical laboratories should embrace caution because they play a vital role in this condition. Before understanding the test is important to understand the pathogenesis of hyperkalemia. Remember homeostasis? The kidneys play a major role in maintaining potassium homeostasis by matching potassium intake with potassium excretion. Potassium is freely filtered by the glomerulus and 90-95% is reabsorbed in the proximal tubule and loop of Henle. Urinary excretion of potassium begins in the distal convoluted tubule and is further regulated by the distal nephron and collecting duct. Therefore, loss of nephron function due to kidney disease results in renal retention of potassium. The main regulators of this process are aldosterone and serum potassium level.
FUNCTIONS OF POTASSIUM IN A HUMAN BODY
1. Serves as an electrolyte-Electrolytes are substances that help conduct electricity in your body. Potassium is one of the most important electrolytes in the human body, with others including chloride, calcium, phosphorus, magnesium and sodium.
2. Muscular function-Potassium is particularly important for the ability of your skeletal and smooth muscles to contract.Because of this, an adequate intake of potassium is important for regular digestive and muscular functioning. Potassium is also vital to the health of your heart, as a normal heart rhythm arises from optimal muscular functioning. This is especially apparent if you have excessively high or low potassium levels, both of which can cause an irregular heartbeat. As heart arrhythmias are potentially life-threatening, you should always maintain an adequate daily intake of potassium.
3. Blood pressure - A balance of sodium and potassium is important for your body's electrolyte functions. As your body works hard to maintain this balance, you can reduce the impact of a high sodium intake by consuming more potassium. Because of sodium's impact on your blood pressure, a boost in your daily potassium intake can help you to maintain a healthy blood pressure or lower it to healthy levels.
N/B: For hypertensive patients you cannot rely entirely on sodium and potassium to lower your blood pressure. In addition to obtaining regular exercise, your intake of fats, salt, cholesterol, protein, fiber, calcium and magnesium can also impact your blood pressure.
CAUSES OF HYPERKALEMIA
The causes are grouped into three,namely; Excessive load, trans cellular potassium shift and reduced renal excretion.
Excessive load:
1. Large packed red cell transfusions
2. Medications – high dose penicillin G
3. Errors in IV KCl dose calculation
4. Liquid formulas and foods (salt substitutes)
5. Excessive cellular damage from trauma, burns
Transcellular K+ shift :
1. Acidosis
2. Insulin deficiency
3. Hyperosmolarity
4. Non specific
5. In burns, cord injury and trauma patients.
Reduced renal excretion
1. Renal failure
2. Inherited or acquired tubular dysfunction
3. Mineralocorticoid deficiency
4. Drug effect
5. Hypovolemia
LABORATORY DIAGNOSIS
Whenever there is a requisition for potassium tests all laboratory professionals including phlebotomists should be take precaution besides adherence to SOPs . The test results may be "messed up" either in pre-analytical,analytical or post analytical stages. This procedure has grave consequences, patients die from misdiagnosis all the time, we want to be in the war-front preventing deaths not accelerating them.
Internal quality controls should be done before running this test, that shouldn't be debated, you could be using a faulty equipment or the personnel not fit run the procedure. Sometimes laboratory practitioners avoid doing internal QC for various reasons that are not worthy compromising patients lives i.e cost incurred on running the QC or delayed TAT. Besides the QC on pre-nalytical stage, sample collection plays a crucial role in diagnosis of hyperkalemia. Avoid poor phlebotomy. The following are some things to avoid that result in pseudohyperkalemia or unexplained results;
1. Insufficient samples
2. Overcentrifugation especially at high Speed.
3. Tourniquet tied more than a minute
4. Use of improperly clotted samples
5. Samples stayed longer before separation-delayed processing
6. Poor storage of samples
7. Ethanol containing antiseptics are not allowed to dry completely before venipuncture.
8. Patient factors - Fear of imminent venipuncture or crying associated with hyperventilation (even for 3-6 min) is associated with acute respiratory alkalosis, which results in a significant hyperkalemic response mediated by enhanced alpha-adrenergic activity.
9. Contaminants- Potassium containing IV fluids are common contaminants as are potassium salts of tube additives. If the recommended order of draw during phlebotomy is not maintained, carryover and back flow of potassium salts of tube additives such as ethylenediamine tetra-acetic acid (EDTA) or oxalate can elevate measured potassium.
10. Mislabelling of samples - Just because its an emergency test doesn't mean you just label with one name!
NORMAL RANGES
3.5-5.5mmol/L
Also read on hypokalemia
References.
1. Hishiki K, Toyama M, Sato R, Suzuki I, Kisugi R, Koike M, et al. Draft proposal to estimate true values of serum potassium in samples from patients with myeloproliferative neoplasma. Rinsho Byori. 2012;60:516–22. [PubMed]
2. Brescia V, Tampoia M, Mileti A. Evaluation of factitious hyperkalemia in hemolytic samples: Impact of the mean corpuscular hemoglobin concentration. Lab Med. 2009;40:224–6.
3. Hawkins R. Variability in potassium/hemoglobin ratios for hemolysis correction. Clin Chem. 2002;48:796. [PubMed]
4. Shepherd J, Warner MH, P**n P, Kilpatrick ES. Use of haemolysis index to estimate potassium concentration in in-vitro haemolysed serum samples. Clin Chem Lab Med. 2006;44:877–9. [PubMed]
