Renal tubular acidosis (RTA) is a disorder that has improper function of renal acid-base regulation and is rarely encountered during pregnancy. Currently, there is no clear evidence on management and outcomes in patients with this condition. We report a case of a previously healthy 23-year-old female at 30 weeks of gestation who presented with proximal RTA and had spontaneous resolution of the condition shortly after delivery.
Renal tubular acidosis (RTA) is a group of disorders that are defined by defective renal acid-base regulation. The disease can be inherited, acquired, or idiopathic. RTA is classified into three major forms, which include distal (type 1), proximal (type 2), and hyperkalemic (type 4) forms. Distal RTA is characterized by decreased urinary acid secretion, proximal RTA has an impaired bicarbonate reabsorption, and hyperkalemic RTA is either an aldosterone deficiency or resistance [
RTA is rarely encountered during pregnancy and commonly has been reported with maternal substance abuse, such as toluene [
We report a case of transient proximal RTA in a previously healthy 23-year-old patient at 30 weeks of gestation that spontaneously resolved after delivery.
A 23-year-old previously healthy African American female, gravida 5 para 4, with no significant past medical history presented at 30 weeks of gestation with complaints of generalized weakness and fatigue for the previous two weeks. Review of systems was only significant for polyuria and polydipsia. Physical examination revealed normotensive blood pressure (122/66 mmHg), normal heart rate (72 beats per minute), and a fundus height that was consistent with 30 weeks of gestation. She had no other notable physical exam findings.
Labs revealed WBC 6.5 cells/uL, hemoglobin 13 g/dL, platelets 350, sodium 135 mmol/L, potassium 1.6 mmol/L, chloride 115 mmol/L, bicarbonate 14 mmol/l, BUN 2 mg/dL, creatinine 0.7 mg/dL, glucose 74 mg/dL, albumin 2.5 gm/dL, calcium 8.7 mg/dL, magnesium 2.1 mEq/L, and corrected serum anion gap of 10.55. Arterial blood gas revealed pH of 7.33, PCO2 25 mmHg, PO2 110 mmHg, and bicarbonate 13.2 moll/L. Urine studies were significant for urine pH of 5, urine anion gap of −1 (urine sodium 80 mmol/L, urine potassium 40 mmol/L, and urine chloride 121 mmol/L), and transtubular potassium gradient of 18 (serum osmolality 275 mosm/dL/L, urine osmolality 380 mosm/dL, urine potassium 40 mmol/L, and serum potassium 1.6 mmol/l), and both urine protein and glucose were negative.
The patient was subsequently diagnosed with type 2 (proximal) RTA based on the laboratory data ordered above. ANA, anti-SSA, anti-SSB, anti-dsDNA, anti-Smith, HIV, TSH, and hepatitis panel were all normal/nonreactive. During the hospital stay, she initially received a sodium bicarbonate drip totaling 300 mEq. This was eventually transitioned to potassium citrate 20 mEq orally three times per day. After one week, she underwent a spontaneous vaginal delivery of a premature fetus; however the baby died shortly after delivery secondary to respiratory failure. The patient was seen at a two-week follow-up visit in the outpatient clinic where serum potassium was 4.3 and serum bicarbonate was 27 mmol/L. Our patient did not require any further potassium or bicarbonate supplementation after pregnancy and her supplementation was then discontinued.
The kidney has an important role in maintaining normal systemic acid base by controlling bicarbonate reabsorption and acid secretion. Loss of some tubular function can prevent the kidney from maintaining this balance [
Distal RTA (type 1) is the most common form of primary RTA in most Western countries. Distal RTA occurs due to the inability of the renal tubules to decrease urine pH and increase urinary ammonium excretion during sustained hyperchloremic metabolic acidosis and hypokalemia [
Proximal RTA (type 2) is associated with a decreased ability of the proximal nephron to reabsorb bicarbonate. Patients with proximal RTA can be asymptomatic or as in our case present with weakness and paralysis secondary to severe hypokalemia. The hyperchloremic metabolic acidosis in proximal RTA is usually less severe because the tubular system is still capable of retaining bicarbonate distally [
There is a further subdivision of proximal RTA, which is a rare condition called isolated proximal RTA. This form can either be classified as an autosomal dominant, autosomal recessive, or sporadic isolated proximal RTA. In either the autosomal dominant or recessive form, the RTA usually is a lifelong condition after presentation. However, the sporadic isolated proximal RTA is typically a sporadic event that resolves sometime after treatment [
Pregnancy is reported to worsen either type of RTA. In pregnancy, there is an understood mild physiological respiratory alkalosis and a hyperfiltration in the kidneys secondary to increased blood volume. This hyperfiltration results in an increased loss of some electrolytes leading to a higher requirement of potassium and bicarbonate [
Reported cases and outcomes of renal tubular acidosis (RTA) that presented during pregnancy [
Case | Year | Type of RTA | Outcome |
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Srisuttayasathien | 2015 | Distal RTA | Rhabdomyolysis induced by hypokalemia from distal RTA; successful delivery and being healthy on follow-up. |
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Mallett et al. | 2011 | Distal RTA (ibuprofen related) | Distal RTA induced by ibuprofen and codeine abuse that resolved after delivery of healthy baby at 37 weeks. Some renal dysfunction persisted on follow-up. |
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Muthukrishnan et al. | 2010 | Distal RTA | Persistent hypokalemia leading to rhabdomyolysis; successful delivery and complete resolution of symptoms. |
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Firmin et al. | 2007 | Proximal RTA | Delivery of a healthy infant; mild persistence of hypokalemia at 1-year follow-up. |
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Seoud et al. | 2000 | Transient RTA | Delivery of a healthy infant; complete resolution of symptoms at follow-up. |
There are some case reports of RTA presenting for the first time in pregnant patients as seen in Table
Previous reports of RTA in pregnancy, however, have offered little discussion on the effects of RTA on fetal development [
Also, in our case, the patient had no previous past medical history and spontaneously began having hypokalemia symptoms from her sporadic RTA. The patient did not have any evident causes of her disease and did not report any family history or prior complications with previous pregnancies. Seoud et al. reported their patient with proximal RTA initially presented with preterm labor. Their case also resulted in resolution of electrolyte abnormalities in less than a year after delivery [
The patient had no systemic disorders and her electrolyte abnormalities quickly resolved after delivery of the preterm fetus. This leads us to believe that our case was isolated sporadic proximal RTA induced during pregnancy. Unfortunately, our patient presented several weeks after being symptomatic, which led to delayed acidosis correction and a preterm delivery. The newborn had respiratory failure and died shortly after birth. It is unclear if earlier treatment would have prevented this outcome.
In conclusion, we presented a very rare case of isolated sporadic proximal RTA (type 2) in a previously healthy pregnant patient. She has no past medical history and no clear inciting causes of her presenting condition. She responded well to treatment and one week later delivered a preterm infant who did not survive. Shortly after her delivery, she spontaneously and completely resolved her condition no longer needing any treatment for RTA.
The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.