After a 5-month-old boy stopped growing, doctors found "worrisome abnormalities" in his blood, including potentially fatal sodium levels—then tests confirmed the infant's diagnosis, Lisa Sanders writes for the New York Times Magazine.

Expedite patient diagnosis

Blood tests detect 'worrisome abnormalities'

Since birth, the 5-month-old boy had trouble with breast and bottle feeding. He hadn't gained any weight since he was two months old.

"Other than his size, he looked healthy," Sanders writes. "He was active. He was able to meet all his milestones. He could hold his head up. He could roll over. His fontanel, the soft spot on the top of his head, was flat — as it should be."

The infant's pediatrician told his parents to be patient, but when he still was not gaining weight at his 4-month visit, the doctor decided to take blood samples.

According to Sanders, blood tests detected "worrisome abnormalities" in the boy's blood chemistry. "The salt level in his blood was very high, so high it could induce a seizure. It was so high, in fact, that if it wasn't addressed, he could die."

After receiving their son's test results, the parents took the infant to Blank Children's Hospital, where additional blood tests confirmed that his sodium level was 159—more than 10 points higher than normal.

While the boy's test results indicated that he had too much sodium in his blood, they also indicated that he did not have enough water in his body.

Typically, the brain triggers the urge to increase water intake when there is too much sodium in the body. In addition, the brain will tell the kidneys to retain as much water as possible.

The brain uses a hormone called vasopressin to send these signals to the body. Issues with vasopressin can cause a disorder known as diabetes insipidus (DI), which results in the production of "profuse and watery (insipid) urine," Sanders writes.

Based on the infant's symptoms, doctors suspected he had DI. "His high sodium level should have made his brain send a vasopressin message to his kidneys to hold on to all the water they could. And yet his urine was almost all water," Sanders notes.

'Failure to thrive'

To help treat his symptoms, the doctors prescribed two drugs that trigger the kidneys to purge sodium. Soon after, the baby's sodium levels fell, suggesting their suspected diagnosis of DI was correct. However, they still needed to determine if the problem stemmed from the brain or the kidneys to determine how to treat it. 

They ordered an MRI to look for issues in the pituitary, which came back normal. His doctors decided the problem was most likely in his kidneys. They took samples for a genetic test, but the results would take weeks.

The boy was admitted to the ED with the diagnosis "failure to thrive." He was still in the zero percentile on the growth chart. On the medication, the boy's sodium levels slowly decreased. After a few days, his blood chemistries were completely normal. The doctors sent the boy home and told his parents that he should start gaining weight.

But he didn't. Worried that their son could be running out of time, the boy's parents took him to see genetics specialists at the University of Iowa Stead Family Children's Hospital.

Then, they were referred to pediatric kidney specialist Pat Brophy, who recommended placing a gastrostomy or G tube into the boy's stomach to make sure he was absorbing his calories, medications, and supplemental water.

As various test results started to come back negative, "the baby's parents could see that he was improving just by getting the calories and especially the water he needed," Sanders writes.

By the time the boy was cleared to leave the hospital two weeks later, he had already gained more than a pound.

A couple months later as the boy was beginning to get back on the growth curve, the results of his genetic tests came back confirming what the doctors already knew—the boy had DI.

Learning to live with DI

According to Sanders, the boy is now seven years old. "He is learning to live with his D.I.," Sanders adds. He is still taking the medications that help lower the sodium levels in his body.

"He has to go to the bathroom often. And he must drink lots and lots of water to replace all that he loses in his urine," she writes. "He's not as big as his brothers—not yet, and maybe not ever. But he is still growing and thriving, and as far as his parents are concerned, that's more than enough." (Sanders, New York Times Magazine, 9/1)