Distal renal tubular acidosis: pathogenesis and classification

Primary Distal Renal Tubular Acidosis: Toward an Optimal Correction of Metabolic Acidosis

The term classic, type 1 renal tubular acidosis or primary distal renal tubular acidosis is used to designate patients with impaired ability to excrete acid normally in the urine as a result of tubular transport defects involving type A intercalated cells in the collecting duct. The clinical phenotype is largely characterized by the complications of chronic metabolic acidosis (MA): stunted growth, bone abnormalities, and nephrocalcinosis and nephrolithiasis that develop as the consequence of hypercalciuria and hypocitraturia. All these manifestations are preventable with early and sustained correction of MA with alkali therapy. The optimal target for plasma bicarbonate should be as close as possible to the range considered normal by current standards (between 23 and 28 mEq/L.). Most of the benefits of alkali therapy are tangible early in the course of the disease in childhood, but life-long treatment is required to prevent the vast array of complications attributable to chronic MA.

Urinary Ammonium in Clinical Medicine: Direct Measurement and the Urine Anion Gap as a Surrogate Marker During Metabolic Acidosis

Ammonium is the most important component of urinary acid excretion, normally accounting for about two-third of net acid excretion. In this article, we discuss urine ammonium not only in the evaluation of metabolic acidosis but also in other clinical conditions such as chronic kidney disease. Different methods to measure urine NH₄⁺ that have been employed over the years are discussed. The enzymatic method used by clinical laboratories in the United States to measure plasma ammonia via the glutamate dehydrogenase can be used for urine ammonium. The urine anion gap calculation can be used as a rough marker of urine ammonium in the initial bedside evaluation of metabolic acidosis such as in distal renal tubular acidosis. Urine ammonium measurements, however, should be made more available in clinical medicine for a precise evaluation of this important component of urinary acid excretion.

Secondary distal renal tubular acidosis and sclerotic metabolic bone disease in seronegative spondyloarthropathy

Adults with distal renal tubular acidosis (dRTA) commonly present with hypokalaemia (with/without paralysis), nephrolithiasis/nephrocalcinosis and vague musculoskeletal symptoms. All adults with dRTA should be thoroughly evaluated for systemic diseases, certain medications and toxins. The leading cause of acquired or secondary dRTA in adults is primary Sjögren syndrome (SS); however, other collagen vascular diseases (CVDs) including seronegative spondyloarthropathy (SSpA) may at times give rise to secondary dRTA. Metabolic bone disease is often encountered in adults with dRTA, and the list includes osteomalacia and secondary osteoporosis; sclerotic metabolic bone disease is an extremely rare manifestation of dRTA. Coexistence of dRTA and sclerotic bone disease is seen in primary dRTA due to mutation in CA2 gene and acquired dRTA secondary to systemic fluorosis. Primary SS and SSpA, rarely if ever, may also lead to both secondary dRTA and osteosclerosis. Circulating autoantibodies against carbonic anhydrase II and possibly calcium sensing receptor may explain both these features in patients with CVD.

Hypokalemic Distal Renal Tubular Acidosis

Distal renal tubular acidosis (DRTA) is defined as hyperchloremic, non-anion gap metabolic acidosis with impaired urinary acid excretion in the presence of a normal or moderately reduced glomerular filtration rate. Failure in urinary acid excretion results from reduced H⁺ secretion by intercalated cells in the distal nephron. This results in decreased excretion of NH₄⁺ and other acids collectively referred as titratable acids while urine pH is typically above 5.5 in the face of systemic acidosis. The clinical phenotype in patients with DRTA is characterized by stunted growth with bone abnormalities in children as well as nephrocalcinosis and nephrolithiasis that develop as the consequence of hypercalciuria, hypocitraturia, and relatively alkaline urine. Hypokalemia is a striking finding that accounts for muscle weakness and requires continued treatment together with alkali-based therapies. This review will focus on the mechanisms responsible for impaired acid excretion and urinary potassium wastage, the clinical features, and diagnostic approaches of hypokalemic DRTA, both inherited and acquired.

Hyperkalemic Forms of Renal Tubular Acidosis: Clinical and Pathophysiological Aspects

In contrast to distal type I or classic renal tubular acidosis (RTA) that is associated with hypokalemia, hyperkalemic forms of RTA also occur usually in the setting of mild-to-moderate CKD. Two pathogenic types of hyperkalemic metabolic acidosis are frequently encountered in adults with underlying CKD. One type, which corresponds to some extent to the animal model of selective aldosterone deficiency (SAD) created experimentally by adrenalectomy and glucocorticoid replacement, is manifested in humans by low plasma and urinary aldosterone levels, reduced ammonium excretion, and preserved ability to lower urine pH below 5.5. This type of hyperkalemic RTA is also referred to as type IV RTA. It should be noted that the mere deficiency of aldosterone when glomerular filtration rate is completely normal only causes a modest decline in plasma bicarbonate which emphasizes the importance of reduced glomerular filtration rate in the development of the hyperchloremic metabolic acidosis associated with SAD. Another type of hyperkalemic RTA distinctive from SAD in which plasma aldosterone is not reduced is referred to as hyperkalemic distal renal tubular acidosis because urine pH cannot be reduced despite acidemia or after provocative tests aimed at increasing sodium-dependent distal acidification such as the administration of sodium sulfate or loop diuretics with or without concurrent mineralocorticoid administration. This type of hyperkalemic RTA (also referred to as voltage-dependent distal renal tubular acidosis) has been best described in patients with obstructive uropathy and resembles the impairment in both hydrogen ion and potassium secretion that are induced experimentally by urinary tract obstruction and when sodium transport in the cortical collecting tubule is blocked by amiloride.

Hyporeninemic hypoaldosteronism in a patient with diabetes mellitus: an unforgettable case report

A 58-year-old man presented with a 3-year history of chronic and intermittent hyperkalemia requiring recurrent attendances to the emergency department for urgent treatment. His medical history included secondary diabetes mellitus following a bout of acute pancreatitis and a previous splenectomy for a spontaneous splenic rupture. He also had a history of prolonged use of non-steroidal anti-inflammatory drugs for back pain and painful neuropathy. He was not on any medication or diet that would cause a raised serum potassium level and his renal function was normal. He was on a basal-bolus insulin regimen but his diabetes control had been poor for several years. As the hyperkalemia had gone on for so long in the presence of normal renal function, he went on to have further tests. Adrenal insufficiency had been ruled out following a short Synacthen test. Further investigations revealed low serum aldosterone levels and inappropriately low serum renin levels in the presence of hyperkalemia. This was suggestive of hyporeninemic hypoaldosteronism (HH). He was then treated with fludrocortisone and furosemide and his serum potassium levels remained normal. Additionally, he did not require any more emergency admissions to treat hyperkalemia thereafter. It was concluded that the HH-induced hyperkalemia was caused by diabetes mellitus or due to a combination of diabetes and prolonged use of non-steroidal anti-inflammatory drugs. The absence of renal impairment may have contributed to the delay in diagnosis. HH is a commonly overlooked cause of hyperkalemia. This case highlights the fact that it should always be suspected when unexplained hyperkalemia is found in patients with only mild-moderately impaired renal function, especially in the presence of diabetes mellitus.

Medication treatment complexity and adherence in children with CKD

BACKGROUND AND OBJECTIVES

The complexity of CKD management in children is increased by the number of comorbid conditions. This study assessed the prevalence of comorbidities in pediatric CKD and the frequency with which multiple comorbidities present together by assessing prevalent medication use by CKD stage and diagnosis and their association with clinical or sociodemographic factors. The association between number and frequency of dosing of medications prescribed and self-report of nonadherence was also assessed.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this cross-sectional analysis of the Chronic Kidney Disease in Children study, medication use at study entry grouped by indication was examined by CKD stage, diagnosis, age, race, ethnicity, income, and CKD duration. Multivariate adjusted predictors of medication use and clustering were examined. Nonadherence was assessed by self-report of missed medications in the past 7 days.

RESULTS

The 558 eligible participants had a median age of 11 years and median GFR of 44 ml/min per 1.73 m(2); 62% of participants were male and 78% had nonglomerular kidney disease. The number of medications for treatment of CKD comorbidities increased with advanced CKD stage (2.5-fold for stages IV versus II; P<0.001) and glomerular disease (1.4-fold versus nonglomerular; P<0.001). Three distinct medication clusters were identified that corresponded to treatment of glomerular disease, advanced renal tubular dysfunction, and proteinuric complications, respectively. Nonadherence was associated with increased medication dosing frequency (administration >2 times/d; P<0.001) but not the number of medications.

CONCLUSIONS

Medical therapy for children with CKD is complex and is affected by glomerular diagnosis, CKD stage, and medication frequency. The need for CKD-related medication treatment cannot be easily predicted by CKD staging alone. Poorer adherence was associated with increased medication frequency, but not with the number of medical problems needing treatment. Consolidating medical treatment and reducing medication frequency may improve adherence rates in children with CKD.

[Tubular renal acidosis]

Renal tubular acidosis (RTAs) are a group of metabolic disorders characterized by metabolic acidosis with normal plasma anion gap. There are three main forms of RTA: a proximal RTA called type II and a distal RTA (type I and IV). The RTA type II is a consequence of the inability of the proximal tubule to reabsorb bicarbonate. The distal RTA is associated with the inability to excrete the daily acid load and may be associated with hyperkalaemia (type IV) or hypokalemia (type I). The most common etiology of RTA type IV is the hypoaldosteronism. The RTAs can be complicated by nephrocalcinosis and obstructive nephrolithiasis. Alkalinization is the cornerstone of treatment.

Genetic causes and mechanisms of distal renal tubular acidosis

The primary or hereditary forms of distal renal tubular acidosis (dRTA) have received increased attention because of advances in the understanding of the molecular mechanism, whereby mutations in the main proteins involved in acid-base transport result in impaired acid excretion. Dysfunction of intercalated cells in the collecting tubules accounts for all the known genetic causes of dRTA. These cells secrete protons into the tubular lumen through H(+)-ATPases functionally coupled to the basolateral anion exchanger 1 (AE1). The substrate for both transporters is provided by the catalytic activity of the cytosolic carbonic anhydrase II (CA II), an enzyme which is also present in the proximal tubular cells and osteoclasts. Mutations in ATP6V1B1, encoding the B-subtype unit of the apical H(+) ATPase, and ATP6V0A4, encoding the a-subtype unit, lead to the loss of function of the apical H(+) ATPase and are usually responsible for patients with autosomal recessive dRTA often associated with early or late sensorineural deafness. Mutations in the gene encoding the cytosolic CA II are associated with the autosomal recessive syndrome of osteopetrosis, mixed distal and proximal RTA and cerebral calcification. Mutations in the AE1, the gene that encodes the Cl(-)/HCO(3)(-) exchanger, usually present as dominant dRTA, but a recessive pattern has been recently described. Several studies have shown trafficking defects in the mutant protein rather than the lack of function as the major mechanism underlying the pathogenesis of dRTA from AE1 mutations.

Severe life-threatening hypokalemia in a cat with suspected distal renal tubular acidosis

OBJECTIVE

Description of the clinical presentation and management of a critically ill cat with profound hypokalemia associated with a suspicion of distal renal tubular acidosis (DRTA) and secondary hyperaldosteronism.

CASE SUMMARY

A cat was presented with severe generalized weakness and acute ventilatory failure associated with severe hypokalemia. The acid-base analysis and complete analytical profile of the urine confirmed the presence of a normal anion-gap metabolic acidosis with a urine pH of 7, a disorder consistent with DRTA. The high plasma renin activity, high aldosterone concentration, and low normal plasma aldosterone concentration/plasma renin activity ratio suggested secondary hyperaldosteronism. The management of the patient in the ICU was successful. No identifiable cause could be determined as a cause for the DRTA, so the disorder was assumed to be the primary problem.

NEW OR UNIQUE INFORMATION PROVIDED

DRTA is a rare disorder occasionally reported in the veterinary literature; it is especially rare in cats. Complete diagnostic evaluation was necessary to identify the reported disorders as the cause of the clinical presentation. To the author's knowledge, this is the first case reporting DRTA, and a simultaneously documented mineralocorticoid response, as a cause of a life-threatening hypokalemia.

Hypokalaemic paralysis precipitated by distal renal tubular acidosis secondary to Sjögren's syndrome

A 43-year-old woman presented with a sudden onset of hypokalaemic paralysis requiring intubation and ventilatory support. Subsequent biochemical and clinical assessments established a diagnosis of distal renal tubular acidosis (RTA) in association with underlying Sjögren's syndrome as the aetiology of her profound hypokalaemia. Distal RTA is rare, but Sjögren's syndrome is one of the more common causes in adults and should be considered in the differential diagnosis of patients who present with hypokalaemic muscular paralysis.

Distal renal tubular acidosis and the potassium enigma

Severe hypokalemia is a central feature of the classic type of distal renal tubular acidosis (RTA), both in hereditary and acquired forms. In the past decade, many of the genetic defects associated with the hereditary types of distal RTA have been identified and have been the subject of a number of reviews. These genetic advances have expanded our understanding of the molecular mechanisms that lead to distal RTA. In this article, we review data published in the literature on plasma potassium from patients with inherited forms of distal RTA. The degree of hypokalemia varies depending on whether the disease is autosomal autosomal-recessive or dominant, but, interestingly, it occurs in defects caused by mutations in genes encoding the AE-1 exchanger, the carbonic anhydrase II gene, and genes encoding different subunits of the H+ adenosine triphosphatase. This shows that a unique defect involving the H+/K+-adenosine triphosphatase leading to renal potassium wastage cannot explain the hypokalemia seen in virtually all types of classic distal RTA.

ATP6B1 gene mutations associated with distal renal tubular acidosis and deafness in a child

A large proportion of autosomal recessive distal renal tubular acidosis (RTA) is associated with mutations in the ATP6B1 gene encoding the B1 subunit of H+-ATPase. H+-ATPase is one of the key membrane transporters for net acid excretion in the alpha-intercalated cells of the medullary collecting duct. Sensorineural hearing loss frequently accompanies this type of distal RTA. Mutational analysis of the ATP6B1 gene in a 9-year-old Korean boy with distal RTA and sensorineural hearing loss found 2 heterozygous missense point mutations. Although a single case report, this is the second report documenting ATP6B1 mutations in recessive distal RTA with sensorineural hearing loss after the original report by Karet et al and confirms the novelty of these mutations.

Hereditary distal renal tubular acidosis: new understandings

The primary or hereditary form of distal renal tubular acidosis (dRTA), although rare, has received increased attention recently because of dramatic advances in the understanding of its genetic basis. The final regulation of renal acid excretion is effected by various acid/base transporters localized in specialized cells in the cortical collecting and outer medullary collecting tubules. Inherited defects in two of the key acid/base transporters involved in distal acidification, as well as mutations in the cytosolic carbonic anhydrase gene, can cause dRTA. The syndrome is inherited in both autosomal dominant and recessive patterns; patients with recessive dRTA present with either acute illness or growth failure at a young age, sometimes accompanied by deafness, whereas dominant dRTA is usually a milder disease and involves no hearing loss. The AE1 gene encodes two Cl-/HCO3- exchangers that are expressed in the erythrocyte and in the acid-secreting intercalated cells of the kidney. AE1 contributes to urinary acidification by providing the major exit route for HCO3- across the basolateral membrane. Several mutations in the AE1 gene cosegregate with dominant dRTA. The modest degree of hypofunction exhibited in vitro by these mutations, however, does not explain the abnormal distal acidification phenotype. Other AE1 mutations have been linked to a recessive syndrome of dRTA and hemolytic anemia in which hypofunction can be discerned by in vitro studies. Several mutations in the carbonic anyhdrase II gene are associated with the autosomal recessive syndrome of osteopetrosis, renal tubular acidosis, and cerebral calcification. Some of these individuals present with deafness of the conductive type. By contrast, more recent studies have shown that mutations in ATP6B1, encoding the B-subtype unit of the apical H(+) ATPase, are responsible for a group of patients with autosomal recessive dRTA associated with sensorineural deafness. Thus, the presence of deafness and the type provide an important clue to the genetic lesion underlying hereditary dRTA.

Distal tubule bicarbonate reabsorption in intact and remnant diabetic kidneys

BACKGROUND

In the diabetic patient, hyperkalemia and hyperchloremic metabolic acidosis has been attributed to one or more of the following factors associated with diabetic nephropathy: hypoaldosteronism, altered potassium homeostasis, or a distal tubular (DT) defect in hydrogen ion secretion. To evaluate maximal in vivo DT acidification in streptozotocin (STZ) diabetes, unidirectional bicarbonate reabsorption (JHCO3) was measured in DTs after acid loading and in surviving DT after 2/3 nephrectomy (Nx).

METHODS

Acid gavage induced hyperchloremic metabolic acidosis in four groups of rats: diabetic rats with hyperglycemia two (a) and (b) eight weeks after STZ injection, (c) diabetic rats with tight glucose control two weeks after STZ injection and insulin pump implantation; and (d) control nondiabetic rats. Another group of diabetic rats underwent (e) Nx one week after STZ injection; these rats were neither acid loaded nor pump implanted.

RESULTS

In the acidotic rats, the plasma potassium concentration, the plasma and urine acid-base parameters in the three STZ diabetic groups was not different from control rats, whereas JHCO3 fluxes were brisk without important differences between groups. In Nx rats, although the plasma potassium concentration and acid-base status were normal, surviving JHCO3 fluxes were still brisk and not different from the acid-loaded rats.

CONCLUSIONS

These in vivo measurements indicate there is no impairment in DT unidirectional bicarbonate reabsorption in the intact or remnant STZ diabetic kidney.

An aetiological profile of short stature in the Indian subcontinent

OBJECTIVE

To determine the aetiological causes of short stature in a developing region of the world.

METHODOLOGY

A retrospective analysis was made of data from 193 subjects who were primarily evaluated for short stature in the Endocrinology Department, Institute of Medical Sciences, Kashmir, India. These subjects had a height of more than 3 standard deviations (SD) below the mean for their age and sex, and were seen over a decade (January 1987 to December 1996). A logical and comprehensive clinical and investigative protocol was followed to identify the aetiology of short stature.

RESULTS

Growth hormone deficiency was the commonest identifiable cause of short stature and accounted for 22.8% of cases. Thirty-six subjects (18.7%) had a normal variant short stature. Renal tubular acidosis was diagnosed in 10.4%, primary hypothyroidism, malnutrition and hypothalamic syndrome in 7.8% each, and growth hormone insensitivity syndrome in 4.1% cases.

CONCLUSIONS

We conclude that, in addition to growth hormone deficiency and normal variant short stature, distal renal tubular acidosis and growth hormone insensitivity syndrome are significant causes of short stature in India.

Use of the urine-to-blood carbon dioxide tension gradient as a measurement of impaired distal tubular hydrogen ion secretion among neonates

To evaluate the utility of the urinary-minus-blood partial pressure of carbon dioxide (U-B PCO2) gradient for the diagnosis of distal renal tubular acidosis in neonates, we measured the U-B PCO2 gradient corresponding to different urinary bicarbonate concentrations in 40 neonates. The U-B PCO2 gradient in these neonates had a significant linear relationship to the urinary bicarbonate concentration. When the urinary bicarbonate concentration was > 10 mmol/L, in all the neonates the U-B PCO2 could be increased above the 20 mm Hg level. We conclude that it is appropriate to determine the U-B PCO2 gradient as an index of distal urinary acidification and that it is a necessary test for diagnosis of distal renal tubular acidosis in neonates.

Effect of metabolic acidosis on the expression of insulin-like growth factor and growth hormone receptor

To further our understanding of the growth failure in metabolic acidosis, we examined the insulin-like growth factor (IGF-I and IGF-II), the IGF binding protein-3 (IGFBP-3), and the hepatic IGF mRNA and growth hormone receptor mRNA in control, pair-fed and acidotic rats. The rats in the last group were made acidotic by using ammonium chloride (1.5%) as their sole fluid intake for eight days. Metabolic acidosis was confirmed by a blood pH of 7.11 +/- 0.10 (mean +/- SD). The mean starting weights for all rats were 167.1 +/- 3.4 grams. Growth impairment was observed in the acidotic rats after one week of ammonium chloride intake. The body weights of the acidotic rats compared to those of the control rats were 155.5 +/- 18.9 g versus 222.8 +/- 9.7 g, P < 0.001; the pair-fed rats weighed 156.8 +/- 19.6 grams. All rats were bled and sacrificed on day 8. Sera and tissue were analyzed with the following results: compared to the ad libitum controls, the same IGF-I concentrations were significantly decreased in the acidotic animals (P < 0.02) as well as pair-fed controls (P < 0.005). The serum IGF-II and IGF-binding protein-3 concentrations were unchanged by acidosis or food restriction. The hepatic IGF-I mRNA was significantly reduced by acidosis (P < 0.01) and pair-feeding (P < 0.01). Compared to control, the mean hepatic IGF mRNA in acidosis was significantly lower (P < 0.01). However, there was no significant difference between the acidotic and the pair-fed groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Urine-to-blood carbon dioxide tension gradient and maximal depression of urinary pH to distinguish rate-dependent from classic distal renal tubular acidosis in children

We determined the prevalence and clinical features of rate-dependent distal renal tubular acidosis (dRTA) in 31 children examined for possible renal tubular acidosis by measuring the urinary-minus-blood partial pressure of carbon dioxide (U-B PCO2) gradient, minimal urinary pH, and fractional excretion of bicarbonate. Of 20 patients with low U-B PCO2 gradients, nine could not lower urinary pH < or = 5.5, indicating classic dRTA, whereas 11 could lower urinary pH < or = 5.5, as described in rate-dependent dRTA. When patients with rate-dependent dRTA and classic (type I) dRTA were compared, there was no difference in the mean U-B PCO2 gradient or in clinical findings, including age, reason for referral, presence of nephrocalcinosis, or depression of linear growth. We conclude that children with rate-dependent dRTA are susceptible to at least some of the same sequelae as children with classic dRTA. Measurement of minimal urinary pH will not detect this subtle form of dRTA. Determination of the U-B PCO2 gradient should be considered a routine part of evaluation for suspected renal tubular acidosis in a child.

Recurrent nephrolithiasis in renal tubular acidosis. Metabolic profiles, therapy and course

13 patients with recurrent urolithiasis and distal renal tubular acidosis (RTA I) were investigated for lithogenic metabolic disorders. Treatment was given and the patients observed for periods of up to 10 years.

Transient renal acidification defect during acute infantile diarrhea: the role of urinary sodium

We studied urinary acidification daily during the hospital course of 16 infants with acute gastroenteritis and metabolic acidosis. Urine pH value on admission was higher than 5.5 in 14 (87%) patients. We hypothesized that inappropriate urinary acidification was due to sodium deficiency and inadequate sodium delivery to the distal nephron. Forty-one urinary samples were collected during metabolic acidosis. The mean pH of 24 urine samples with sodium concentration less than 10 mmol/L was significantly higher than the pH of 17 samples with sodium concentration greater than 10 mmol/L (6.04 +/- 0.06 vs 5.19 +/- 0.1; p less than 0.001). The urine ratios of titratable acid to creatinine and of total acidity to creatinine were significantly higher in urine samples containing more sodium (p less than 0.02), whereas the ammonium/creatinine ratio was not. After administration of furosemide or correction of the sodium deficit, appropriate acidification was observed. We conclude that impaired urinary acidification is frequently found during metabolic acidosis in infants with acute gastroenteritis and results from a sodium deficit rather than from transient distal renal tubular acidosis.

Renal tubular hyperkalaemia in childhood

Potassium output from the body is regulated by renal excretion, which takes place predominantly in the late distal and cortical collecting tubules. The accepted model for potassium secretion implies the accumulation of potassium into the cell by the activity of basolateral Na-K-ATPase and its exit through voltage-dependent conductive channels. The factors regulating renal potassium secretion are potassium intake, distal urinary flow, systemic acid-base equilibrium, aldosterone, antidiuretic hormone and, probably, epinephrine. Renal handling of potassium is best studied by the response to the acute administration of furosemide. This loop diuretic not only increases sodium and chloride excretion but also enhances potassium and hydrogen ion excretion and stimulates the renin-aldosterone axis. The term "renal tubular hyperkalaemia" refers to a tubular dysfunction where the hyperkalaemia is disproportionate to any reduction in glomerular filtration rate (GFR) and not due primarily or solely to aldosterone deficiency or to drugs impairing either mineralocorticoid action or tubular transport. The syndromes of renal tubular hyperkalaemia mainly observed in childhood are "chloride shunt" syndrome, hyporeninaemic hypoaldosteronism and primary or secondary pseudohypoaldosteronism. Differential diagnosis between these conditions is easily made if attention is paid to the level of GFR, presence of sodium wasting, activity of the renin-aldosterone axis and renal response to acute administration of furosemide.

The use of the urinary anion gap in the diagnosis of hyperchloremic metabolic acidosis

We evaluated the use of the urinary anion gap (sodium plus potassium minus chloride) in assessing hyperchloremic metabolic acidosis in 38 patients with altered distal urinary acidification and in 8 patients with diarrhea. In seven normal subjects given ammonium chloride for three days, the anion gap was negative (-27 +/- 9.8 mmol per liter) and the urinary pH under 5.3 (4.9 +/- 0.03). In the eight patients with diarrhea the anion gap was also negative (-20 +/- 5.7 mmol per liter), even though the urinary pH was above 5.3 (5.64 +/- 0.14). In contrast, the anion gap was positive in all patients with altered urinary acidification, who were classified as having classic renal tubular acidosis (23 +/- 4.1 mmol per liter, 11 patients), hyperkalemic distal renal tubular acidosis (30 +/- 4.2, 12 patients), or selective aldosterone deficiency (39 +/- 4.2, 15 patients). When the data on all subjects studied were pooled, a negative correlation was found between the urinary ammonium level and the urinary anion gap. We conclude that the use of the urinary anion gap, as a rough index of urinary ammonium, may be helpful in the initial evaluation of hyperchloremic metabolic acidosis. A negative anion gap suggests gastrointestinal loss of bicarbonate, whereas a positive anion gap suggests the presence of altered distal urinary acidification.

The kidney in hypergammaglobulinemic purpura

A 25-year-old woman with long-standing hypergammaglobulinemic purpura developed distal renal tubular acidosis and a urine-concentrating defect. The acidification defect was characterized as suggestive of impaired distal proton secretion by infusion of neutral phosphate. The concentrating defect was a form of acquired nephrogenic diabetes insipidus. On renal biopsy, IgM mesangial nephropathy was found along with multiple large hyaline tubular casts. The renal findings in hypergammaglobulinemic purpura are reviewed.

Segmental characterization of defects in collecting tubule acidification

The aim of this study was to investigate cortical collecting tubule (CCT) function in normal individuals and in patients with distal renal tubular acidosis (DRTA) using furosemide (80 mg orally) as a tool to stimulate H+ and K+ secretion by enhancing Na delivery and transport in this nephron segment. In ten normal subjects, furosemide resulted in a fall in urine pH below 5.5 and an increase in net acid and K+ excretion. These effects were obliterated by amiloride, a drug which decreases transtubular epithelial voltage (lumen-negative) in the CCT by blocking Na reabsorption. In 13 patients with DRTA, defined by failure to lower urine pH below 5.5 during acidemia, three distinctive responses to furosemide were found. In six patients with the hyperkalemic variety, furosemide failed to lower urine pH below 5.5 and resulted in a blunted increase in K+ excretion, thereby suggesting that a normal transtubular voltage in the CCT could not be generated in such patients. In five patients with classic RTA, furosemide failed to lower urine pH below 5.5, but K+ excretion increased normally. The increase in K+ excretion indicated that a normal transtubular voltage in the CCT could be generated, while the inability to lower urine pH denotes the presence of a proton pump defect involving the CCT. In two patients with classic RTA, furosemide resulted in both a normal fall in urine pH and an increase in K+ excretion, thereby indicating that the CCT was normal in regards to both proton pump function and in its ability to generate a normal transtubular voltage.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal tubular acidosis in a case of Shwachman's syndrome

We describe metabolic acidosis in a 15-month-old girl with clinical features of Shwachman's syndrome. Renal function tests indicated that the patient had type 1 renal tubular acidosis. Based on our findings and other reports of renal tubular dysfunction in patients with Shwachman's syndrome, we conclude that it is important to look for a possible renal tubular defect in this syndrome.

Acidification in the medullary collecting duct following ureteral obstruction

A defect in urine acidification has been described in obstructive uropathy. Since the collecting tubule from the inner stripe of the outer medulla (OMCTi) is the major site for distal acidification, isolated OMCTi nephron segments from control rabbits and from rabbits after 24 hr of unilateral (UUO) or bilateral (BUO) ureteral obstruction were studied. Tubules were perfused (4 nliter/min) and bathed with an artificial solution resembling rabbit serum ultrafiltrate, and 3H inulin was incorporated in the perfusate as a volume marker. Water absorption (Jv) was -0.03 +/- 0.03 nliter X mm-1 X min-1 in control tubules, and was significantly (P less than 0.05) negative in UUO (-0.48 +/- 0.12 nliter X mm-1 X min-1) and BUO (-0.29 +/- 0.07 nliter/mm-1 X min-1) tubules, as a result of an inulin leak. Bicarbonate absorption (JHCO3) in control tubules was 11.61 +/- 1.21 pmole X mm-1 X min-1 and was significantly lower in UUO tubules (7.59 +/- 1.09 pmole X mm-1 X min-1, P less than 0.05). JHCO3 in BUO tubules although lower than control (7.96 +/- 2.75 pmole X mm-1 X min-1) did not achieve statistical significance because of a high degree of heterogeneity among tubules. To determine whether the acidification disorder was due to a gradient or capacity defect, the ability of the tubules to lower HCO3- concentration (delta HCO3) at low rate of perfusion (1 nliter/min) was examined. No difference in delta HCO3 was found among the three groups being 8.98 +/- 0.54, 9.95 +/- 1.76, and 8.93 +/- 2.19 mmole in control, UUO and BUO tubules respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperkalemic distal renal tubular acidosis in salt-losing congenital adrenal hyperplasia

Functional indices of distal urinary acidification were assessed in two male infants, aged 1 and 3 months, with salt-losing congenital adrenal hyperplasia. In both cases the diagnosis was sustained by the presence of elevated plasma levels of 17-hydroxyprogesterone, hyponatremia, hyperkalemia, metabolic acidosis and increased plasma renin activity. Both patients were unable to lower urinary pH below 5.9 either during acute ammonium chloride-induced acidosis or after i.v. administration of furosemide. One patient also failed to decrease urine pH below 5.5 and to increase urinary potassium excretion during sodium sulfate infusion. Oral sodium bicarbonate loading was given to both patients but failed to induce a significant increase in the urine minus blood PCO2 gradient. This gradient remained low also after neutral phosphate administration. Repeated studies after acute administration of fludrocortisone in one case or after prolonged administration of hydrocortisone in the other resulted in complete normalization of all functional studies. We conclude that salt-losing congenital adrenal hyperplasia can lead to hyperkalemic distal renal tubular acidosis in early infancy. The defective renal secretion of hydrogen ion and potassium is probably related to the abolishment of the negative potential difference in the cortical collecting tubule induced by the impaired reabsorption of sodium.

Hyporeninemic hypoaldosteronism in a patient with multiple myeloma

A patient with progressive renal failure due to multiple myeloma presented with a mixed acid-base disorder (non-anion gap acidosis and respiratory alkalosis) with persistent severe hyperkalemia. Studies revealed an intact ability to lower urine pH during acid loading, markedly decreased plasma renin and aldosterone concentrations despite volume depletion, and an inappropriately low fractional excretion of potassium. Renal biopsy demonstrated plasma cell infiltration of the renal interstitium and typical proteinaceous intratubular casts. Both proximal and distal renal tubular acidification defects have been described previously in patients with multiple myeloma, but this is the first report of hyporeninemic hypoaldosteronism, hyperkalemia, and hyperchloremic metabolic acidosis in association with renal involvement in multiple myeloma.