Understanding Nephrocalcinosis in NICU Graduates: Calcium Deposits in Tiny Kidneys

By Dr. Namrata Todurkar

Leaving the Neonatal Intensive Care Unit (NICU) with your baby is a momentous occasion, a mix of relief, excitement, and perhaps a touch of anxiety as you navigate follow-up care. One term you might hear during this transition is "nephrocalcinosis" – a complex-sounding word that simply means calcium deposits in the kidneys. While it might sound worrying, understanding why it happens and what it means for your baby can provide clarity and peace of mind.

What is Nephrocalcinosis?

In simple terms, nephrocalcinosis literally means calcium in kidneys. It occurs when calcium salts are deposited within the kidney tissue itself. This is different from larger kidney stones that can pass through the urinary tract. In NICU graduates, these deposits are typically found deeper within the kidney structures.

Why is it So Common in Preemies?

It's actually quite prevalent, affecting up to 40% of premature infants. So, if your little one has been diagnosed, you are certainly not alone! Several factors, often unique to prematurity and the necessary treatments in the NICU, come together to create this condition:

1. Immature Kidneys

A baby's kidneys aren't fully developed, both in structure and function, until around 34-36 weeks of pregnancy. For babies born very prematurely, their kidneys are still maturing after birth. This immaturity makes them more prone to imbalances in handling minerals like calcium.

Specifically, preemie kidneys have relatively long segments where urine travels more slowly, potentially creating favorable conditions for tiny calcium crystals to form, stick, and grow.

2. Imbalance of Stone Factors

Think of it like a delicate balance. Mature kidneys are great at keeping "stone-forming" substances (like calcium and oxalate) in check with "stone-inhibiting" substances (like citrate and magnesium). However, premature kidneys often have:

• More promoters: Increased urinary excretion of calcium, oxalate, and uric acid.

• Fewer inhibitors: Decreased urinary excretion of protective citrate and magnesium.

This imbalance increases the likelihood that calcium deposits will form. Although we are referring here to the term ‘stone’, nephrocalcinosis is NOT equivalent to kidney stones.

3. Necessary Medications

Many essential medications preemies need in the NICU can unfortunately increase the risk of nephrocalcinosis. This includes:

• Diuretics (like furosemide): While critical for managing fluid balance or breathing issues, some diuretics can cause more calcium to be excreted in the urine.

• Steroids: Another important medication for helping preemie lungs and managing other conditions can also contribute.

4. Nutritional Supplements and Nutrition

Growing tiny babies need specific, often concentrated nutrition. The calcium, vitamin D, and other nutrients essential for bone development can, at times, contribute to higher levels in the urine, tipping the balance towards calcium deposition. Even the ratio of calcium to phosphorus in their IV nutrition or specialized formulas can play a role.

5. Genetic Factors

Sometimes, underlying genetic predispositions (mutations in how the kidney handles minerals) can make certain babies more susceptible to developing these deposits.

Essentially, the development of nephrocalcinosis is often a combination of all these factors – the perfect storm of immature kidneys navigating complex, necessary treatments.

The Bright Side: Most Resolve!

Here's the most reassuring part: in 85% of children, nephrocalcinosis resolves naturally within the first few years of life! As your baby's kidneys mature and their overall health stabilizes after the NICU, the conditions that favored deposit formation often improve, and the calcium clears on its own.

Understanding Long-Term Effects and The Importance of Follow-Up

While most cases resolve, doctors monitor babies with nephrocalcinosis closely for a few reasons:

• Potential Risks: Prematurity itself, even without nephrocalcinosis, can be associated with higher blood pressure, relatively smaller kidneys, and long-term kidney function considerations. Having nephrocalcinosis might carry an additional, though still unclear, risk for future kidney health or function.

• Ongoing Management: For infants whose condition is linked to specific medications (like diuretics) or nutritional supplements, adjusting or switching these is often the primary approach to stop further deposits and encourage resolution.

Because of these potential long-term, subtle risks, ongoing and comprehensive follow-up after NICU discharge is essential.

What to Expect in Follow-Up Care

Your baby's follow-up will be tailored to their specific situation (severity, current kidney function, and ongoing therapies). Follow up with a Nephrologist is preferred, although local protocols may vary. Typically, follow-up involves:

• Checking your child’s growth: weight, height, head circumference, body mass index.

• Blood pressure check

• Kidney Ultrasounds: Periodic ultrasounds (perhaps annually for the first few years) to check the size, number, and progression/resolution of the calcium deposits. It's important to know that results can vary slightly depending on the equipment used and who performs the scan, so don't be alarmed if descriptions seem a bit different each time.

• Lab Tests: Simple blood tests (like checking serum creatinine) and urine tests (like calcium-to-creatinine ratio)

What You Can Do as a Parent

• Ask Questions: Never hesitate to ask your medical team detailed questions about your specific baby's situation. Understanding their individual risks, the planned follow-up schedule, and any management strategies is empowering.

• Maintain Follow-Up Appointments: Sticking to the scheduled check-ups and testing is crucial for ensuring your baby's long-term kidney health is monitored and any necessary adjustments in their care are made proactively. Remind your health care provider to check your child’s blood pressure and growth at every visit.

• Be Patient and Positive: Remember that the vast majority of cases resolve completely. Your baby's resilient tiny body is still growing and adapting!

Summary: Nephrocalcinosis in a NICU graduate is a common finding that usually gets better. While it adds another layer to your post-discharge journey, the proactive, comprehensive follow-up care ensures that your baby's kidney health is carefully watched, and that any issues, though uncommon, are addressed early.

Ref:

1. Schell-Feith EA, Kist-van Holthe JE, van der Heijden AJ. Nephrocalcinosis in preterm neonates. Pediatr Nephrol. 2010 Feb;25(2):221-30. doi: 10.1007/s00467-008-0908-9. Epub 2008 Sep 17. PMID: 18797936; PMCID: PMC6941622.

2. Garunkstiene, R., Levuliene, R., Cekuolis, A., Cerkauskiene, R., Drazdiene, N., & Liubsys, A. (2024). A Prospective Study of Nephrocalcinosis in Very Preterm Infants: Incidence, Risk Factors and Vitamin D Intake in the First Month. Medicina, 60(12), 1910. https://doi.org/10.3390/medicina60121910ren 2020, 7, 114; doi:10.3390/children7090114. Cheng Ma, Denisse Broadbent, Garrett Levin, Sanjeet Panda, Devaraj Sambalingam, Norma Garcia, Edson Ruiz and Ajay Pratap Sing

Dr. Namrata Todurkar, MBBS, MD (Pediatrics), DNB (Pediatrics). Fellowship in Neonatology from National Neonatology Forum India. Fellow in Neonatal-Perinatal Medicine at the University of British Columbia. Areas of interest: Neonatal nutrition, Fluid and Electrolyte Management, Inborn Errors, Neurodevelopmental follow-up of preterm infants. Dr. Todurkar is a volunteer blogger at CPBF.