High potassium levels, medically known as hyperkalemia, represent a potentially serious electrolyte imbalance in newborns. Potassium is a positively charged ion necessary for the normal functioning of every cell, particularly those in the heart and muscles, but an excess can be dangerous. In the neonatal period, a serum potassium concentration above 6.5 mmol/L is typically defined as hyperkalemia. This condition is concerning because high potassium levels can destabilize the electrical activity of the heart, leading to life-threatening arrhythmias and cardiac arrest. Understanding the various causes is the first step in addressing this disturbance.
Potassium’s Function and Regulation in the Newborn
Potassium is the most abundant positively charged ion inside the body’s cells, with approximately 98% residing within the intracellular fluid. This concentration gradient is maintained by the sodium-potassium pump, which constantly moves potassium into the cell and sodium out, establishing an electrochemical balance. This proper gradient is essential for nerve signaling and the contraction of all muscle types, including the heart muscle. The kidneys act as the body’s primary regulator of potassium balance, responsible for excreting excess potassium to maintain stable levels in the bloodstream.
Causes Stemming from Reduced Potassium Excretion
One major category of hyperkalemia involves the body’s inability to effectively eliminate potassium through the urine. This is often seen in vulnerable newborns, particularly those born very prematurely.
Prematurity is a significant risk factor, as extremely low birth weight infants often experience Non-Oliguric Hyperkalemia of Prematurity (NOHP) early in life. Their kidneys are structurally and functionally immature, making them inefficient at excreting potassium even when urine output is normal. The renal tubular system responsible for potassium fine-tuning is not fully developed.
Beyond immaturity, Acute Kidney Injury (AKI) can cause hyperkalemia by severely limiting urine production. Conditions that cause a lack of oxygen or blood flow to the kidneys, such as severe sepsis or perinatal asphyxia, can damage the kidney filtering units. When kidney damage is significant, the infant may become oliguric, meaning urine output is drastically reduced, leading to a rapid buildup of potassium.
Adrenal gland disorders can also impair potassium excretion by disrupting hormonal signaling in the kidney. Congenital Adrenal Hyperplasia (CAH), a genetic condition, can lead to a deficiency in the hormone aldosterone. Aldosterone normally signals the kidneys to excrete potassium, so its absence causes the body to retain potassium. Certain medications, such as potassium-sparing diuretics, can mimic this effect by blocking aldosterone’s action.
Causes Stemming from Increased Cellular Potassium Release
A different mechanism for high potassium involves a shift of potassium from inside the cells into the circulating bloodstream. Since 98% of the body’s potassium is stored inside cells, widespread cell damage can rapidly overwhelm the system.
Massive tissue damage, such as severe internal bleeding, extensive bruising, or rhabdomyolysis, causes cell membranes to rupture (cell lysis). This breakdown releases a large volume of intracellular potassium directly into the blood, causing a sharp rise in serum levels. Severe systemic illnesses like sepsis or extensive bowel ischemia can also lead to widespread cell necrosis and potassium release.
A rapid breakdown of red blood cells, known as hemolysis, is another source of potassium release. Red blood cells have a high internal potassium concentration, and conditions like severe Rh incompatibility can cause them to burst. This influx of potassium, combined with a newborn’s limited ability to excrete it, quickly leads to hyperkalemia.
Metabolic Acidosis, where the blood becomes too acidic, can also drive potassium out of cells. To buffer the excess acid, the body shifts hydrogen ions into the cells, which are exchanged for potassium ions moving into the bloodstream. Furthermore, immature sodium-potassium pump function in extremely premature infants can shift potassium out of cells, contributing to non-oliguric hyperkalemia.
Hyperkalemia Due to Sample Collection Issues
A reading of high potassium does not always represent a true physiological problem in the baby. The most common cause of a falsely elevated potassium result is a laboratory artifact called pseudohyperkalemia. This occurs when the potassium level measured in the blood sample is artificially high due to issues during collection or handling.
Newborns, especially premature ones, have small veins, making blood draws technically challenging. Difficult venipuncture or slow collection can cause red blood cells to break down in the test tube before analysis. This in vitro hemolysis releases the cell’s internal potassium into the plasma, which the laboratory registers as a high level.
If a newborn appears otherwise healthy with no signs of illness, a high potassium level should prompt suspicion of a collection error. Because the diagnosis and treatment of true hyperkalemia are urgent, a high reading from a capillary sample (such as a heel stick) is often confirmed immediately with a repeat test from a free-flowing venous or arterial sample. Recognizing pseudohyperkalemia prevents unnecessary and potentially harmful treatment.