Definition

Neonatal hypocalcemia is a common clinical and laboratory abnormality.
The definition relies on total serum calcium (tSCa) or ionized serum calcium (iSCa) cutoffs.
These cutoffs vary between preterm and term neonates.

Gestation	Total Serum Calcium	Ionized Serum Calcium
Preterm	< 7 mg/dL (1.75 mmol/L)	< 4 mg/dL (1 mmol/L)
Term	< 8 mg/dL (2 mmol/L)	< 4.8 mg/dL (1.2 mmol/L)

Pathophysiology And Calcium Homeostasis

Calcium is actively transferred from the mother to the fetus during the last trimester.
Total calcium concentration in cord blood is significantly higher than in maternal serum.
Parathyroid hormone (PTH) and calcitonin do not cross the placental barrier.
Fetal mineral ion homeostasis is mostly independent of vitamin D.
After birth, serum calcium levels start decreasing.
This postnatal drop reaches a nadir of 7.5 to 8.5 mg/dL in healthy term neonates by day 2 of life.
The drop is related to decreased PTH levels and end-organ unresponsiveness to PTH.
Hyperphosphatemia and hypomagnesemia by 12 to 24 hours of age also contribute to this drop.
Body calcium exists mainly in the skeleton (99%) and extracellular fluid (1%).
Extracellular fluid calcium is 40% albumin-bound, 10% anion-bound, and 50% ionized.
Ionized serum calcium is the crucial active form for biochemical processes.
Total serum calcium estimation is a poor substitute for measuring ionized serum calcium.
Falsely low ionized calcium may be recorded in alkalosis or with heparin contamination.

Classification And Etiology

Hypocalcemia is classified into early-onset and late-onset categories.

Early-Onset Neonatal Hypocalcemia (ENH)

Presents within the first 72 to 96 hours of life.
Usually requires short-term calcium supplementation.

Risk Factor	Mechanism
Prematurity	Decreased in-utero transfer of calcium and diminished target organ responsiveness to PTH.
Infants of diabetic mothers	Increased maternal urinary magnesium losses leading to decreased PTH function in the neonate.
Perinatal asphyxia	Cellular damage, renal dysfunction, and phosphate load.
Maternal factors	Maternal hyperparathyroidism or severe maternal vitamin D deficiency.

Late-Onset Neonatal Hypocalcemia (LNH)

Usually presents after 96 hours of life, typically at the end of the first week.
Often symptomatic and generally caused by a high phosphate intake.

Etiology	Examples
Increased phosphate load	Cow milk feeding or renal insufficiency.
Hypoparathyroidism	DiGeorge's syndrome, CATCH 22 syndrome, or maternal hyperparathyroidism.
Iatrogenic causes	Citrated blood products, loop diuretics, lipid infusion, or bicarbonate therapy.
Other conditions	Hypomagnesemia, malabsorption, hepatobiliary disease, or vitamin D deficiency.

Clinical Presentation

Asymptomatic Presentation

Early-onset hypocalcemia is frequently asymptomatic and incidentally detected on screening.

Symptomatic Presentation

Symptoms represent neuromuscular irritability and cardiac involvement.
Neuromuscular signs include jitteriness, myoclonic jerks, exaggerated startle, and seizures.
Cardiac signs include tachycardia, heart failure, and decreased contractility.
Other non-specific symptoms include apnea, cyanosis, tachypnea, vomiting, and laryngospasm.

Diagnosis And Evaluation

First-Line Investigations

Ionized calcium measurement is the preferred mode for diagnosis.
Electrocardiogram (ECG) may show a prolonged QT interval.
QTc greater than 0.45 seconds suggests hypocalcemia.
A diagnosis based only on ECG criteria yields a high false-positive rate.
Suspected cases on ECG must be confirmed with serum calcium measurement.

Second-Line Investigations (For Late-Onset Or Resistant Cases)

Required if hypocalcemia persists or presents late.
Include serum phosphate, magnesium, alkaline phosphatase, parathormone (PTH), and 25-hydroxyvitamin D.

Disorder	Serum Phosphate	Serum Parathormone	Other Findings
Hypoparathyroidism	High	Low	Low 25-OH D.
Pseudohypoparathyroidism	High	High	Low 25-OH D.
Hypomagnesemia	Low	High	Low Magnesium.
Vitamin D Dependent Rickets	Low	High	High Alkaline Phosphatase.

Management

Early-onset asymptomatic hypocalcemia requires 80 mg/kg/day of elemental calcium for 48 hours.
This translates to 8 mL/kg/day of 10% calcium gluconate.
Symptomatic neonates require emergency intravenous bolus therapy under cardiac monitoring.

graph TD
    A[Neonate With Suspected Hypocalcemia] --> B{Are Symptoms Present?}
    B -- Yes --> C[Administer 10% Calcium Gluconate Bolus]
    C --> D[Dose: 2 mL/kg Diluted 1:1 With 5% Dextrose]
    D --> E[Give Slowly Over 10-30 Minutes Under Cardiac Monitoring]
    E --> F[Start Continuous IV Infusion]
    B -- No --> F[Start Continuous IV Infusion]
    F --> G[Dose: 80 mg/kg/day Elemental Calcium For 48 Hours]
    G --> H{Do Seizures Persist?}
    H -- Yes --> I[Suspect Hypomagnesemia]
    I --> J[Administer 50% Magnesium Sulfate 0.2 mL/kg IM]
    H -- No --> K[Taper Calcium Dose By 50% For 24 Hours Then Stop]

Treatment Of Resistant Hypocalcemia

Symptomatic hypocalcemia unresponsive to adequate calcium is usually due to hypomagnesemia.
Administer two doses of 0.2 mL/kg of 50% magnesium sulfate injection deeply intramuscularly 12 hours apart.
Late-onset hypocalcemia with high phosphate load requires discontinuation of animal milk.
Hypoparathyroidism requires calcium supplementation along with active vitamin D therapy.

Precautions And Complications

Bradycardia and arrhythmia are known side effects of bolus intravenous calcium.
Bolus doses must be diluted 1:1 with 5% dextrose and given slowly.
Hepatic necrosis may occur if an umbilical venous catheter tip lies in a portal vein branch.
The umbilical artery catheter must never be used for giving calcium injections.
Accidental injection into the umbilical artery causes arterial spasms and intestinal necrosis.
Extravasation of calcium into subcutaneous tissue causes severe tissue necrosis.
Intravenous sites must be checked frequently during infusion.