Because renal excretion is the primary means of eliminating acid from the body, there is consequently a tendency towards acidemia.

This leads to the clinical features of dRTA:

- Normal anion gap metabolic acidosis/acidemia

- Hypokalemia

- Urinary stone formation (related to alkaline urine, hypercalciuria, and low urinary citrate).

- Nephrocalcinosis (deposition of calcium in the substance of the kidney)

- Bone demineralisation (causing rickets in children and osteomalacia in adults)

The symptoms and sequelae of dRTA are variable and range from being completely asymptomatic, to loin pain and hematuria from kidney stones, to failure to thrive and severe rickets in childhood forms as well as possible renal failure and even death.

dRTA commonly leads to sodium loss and volume contraction, which causes a compensatory increase in blood levels of aldosterone. Aldosterone causes increased resorption of sodium and loss of potassium in the collecting duct of the kidney, so these increased aldosterone levels cause the hypokalemia which is a common symptom of dRTA.

Proximal renal tubular acidosis (pRTA) or Type 2 Renal tubular acidosis (RTA) is a type of RTA caused by a failure of the proximal tubular cells to reabsorb filtered bicarbonate from the urine, leading to urinary bicarbonate wasting and subsequent acidemia. The distal intercalated cells function normally, so the acidemia is less severe than dRTA and the urine can acidify to a pH of less than 5.3. pRTA also has several causes, and may occasionally be present as a solitary defect, but is usually associated with a more generalised dysfunction of the proximal tubular cells called Fanconi syndrome where there is also phosphaturia, glycosuria, aminoaciduria, uricosuria and tubular proteinuria.

Patients with type 2 RTA are also typically hypokalemic due to a combination of secondary hyperaldosteronism, and potassium urinary losses - though serum potassium levels may be falsely elevated because of acidosis. Administration of bicarbonate prior to potassium supplementation might lead to worsened hypokalemia, as potassium shifts intracellularly with alkanization.

The principal feature of Fanconi syndrome is bone demineralization (osteomalacia or rickets) due to phosphate and vitamin D wasting.

Familial disorders

- Cystinosis

- Galactosemia

- Glycogen storage disease (type I)

- Hereditary fructose intolerance

- Lowe syndrome

- Tyrosinemia

- Wilson's disease

Acquired disorders

- Amyloidosis

- Multiple myeloma

- Paroxysmal nocturnal hemoglobinuria

- Toxins, such as HAART, ifosfamide, lead, and cadmium

Proximal RTA (pRTA) is caused by a failure of the proximal tubular cells to reabsorb filtered bicarbonate from the urine, leading to urinary bicarbonate wasting and subsequent acidemia. The distal intercalated cells function normally, so the acidemia is less severe than dRTA and the alpha intercalated cells can produce H to acidify the urine to a pH of less than 5.3. pRTA also has several causes, and may occasionally be present as a solitary defect, but is usually associated with a more generalized dysfunction of the proximal tubular cells called Fanconi syndrome, in which there is also phosphaturia, glycosuria, aminoaciduria, uricosuria, and tubular proteinuria.

The principle feature of Fanconi syndrome is bone demineralization (osteomalacia or rickets) due to phosphate wasting.

Distal RTA (dRTA) is the classical form of RTA, being the first described. Distal RTA is characterized by a failure of H+ secretion into lumen of nephron by the alpha intercalated cells of the medullary collecting duct of the distal nephron.

This failure of acid secretion may be due to a number of causes, and it leads to an inability to acidify the urine to a pH of less than 5.3. Because renal excretion is the primary means of eliminating from the body, there is consequently a tendency towards acidemia. There is an inability to excrete H while cannot be reclaimed by the cell, leading to acidemia (as builds up in the body) and hypokalemia (as cannot be reabsorbed by the alpha cell).

This leads to the clinical features of dRTA; In other words, the intercalated cells' apical H+/K+ antiporter is non-functional, resulting in proton retention and potassium excretion. Since calcium phosphate stones demonstrate a proclivity for deposition at higher pHs (alkaline), the substance of the kidney develops stones bilaterally; this does not occur in the other RTA types.

- Normal anion gap metabolic acidosis/acidemia

- Hypokalemia, Hypocalcemia, Hyperchloremia

- Urinary stone formation (related to alkaline urine, hypercalciuria, and low urinary citrate).

- Nephrocalcinosis (deposition of calcium in the substance of the kidney)

- Bone demineralisation (causing rickets in children and osteomalacia in adults)

- Sjogren's syndrome

Distal renal tubular acidosis (dRTA) or Type 1 renal tubular acidosis (RTA) is the classical form of RTA, being the first described. Distal RTA is characterized by a failure of acid secretion by the alpha intercalated cells of the cortical collecting duct of the distal nephron. This failure of acid secretion may be due to a number of causes, and it leads to an inability to acidify the urine to a pH of less than 5.3.

In general, the cause of a hyperchloremic metabolic acidosis is a "loss of base", either a gastrointestinal loss or a renal loss.

- Gastrointestinal loss of bicarbonate ()

- Severe diarrhea (vomiting will tend to cause hypochloraemic alkalosis)

- Pancreatic fistula with loss of bicarbonate rich pancreatic fluid

- Nasojejunal tube losses in the context of small bowel obstruction and loss of alkaline proximal small bowel secretions

- Chronic laxative abuse

- Renal causes

- Proximal renal tubular acidosis with failure of resorption

- Distal renal tubular acidosis with failure of secretion

- Long-term use of a carbonic anhydrase inhibitor such as acetazolamide

- Other causes

- Ingestion of ammonium chloride, hydrochloric acid, or other acidifying salts

- The treatment and recovery phases of diabetic ketoacidosis

- Volume resuscitation with 0.9% normal saline provides a chloride load, so that infusing more than 3-4L can cause acidosis

- Hyperalimentation ("i.e.", total parenteral nutrition)

Hyperchloremic acidosis is a form of metabolic acidosis associated with a normal anion gap, a decrease in plasma bicarbonate concentration, and an increase in plasma chloride concentration (see anion gap for a fuller explanation). Although plasma anion gap is normal, this condition is often associated with an "increased" urine anion gap, due to the kidney's inability to secrete ammonia.

Dent's disease often produces the following signs and symptoms:

- Extreme thirst combined with dehydration, which leads to frequent urination

- Nephrolithiasis (kidney stones)

- Hypercalciuria (high urine calcium - >300 mg/d or >4 mg/kg per d) with normal levels blood/serum calcium)

- Aminoaciduria (amino acids in urine)

- Phosphaturia (phosphate in urine)

- Glycosuria (glucose in urine)

- Kaliuresis (potassium in urine)

- Hyperuricosuria (excessive amounts of uric acid in the urine)

- Impaired urinary acidification

- Rickets

In a study of 25 patients with Dent's disease, 9 of 15 men, and one of 10 women suffered end-stage kidney disease by the age of 47.

The clinical features of proximal renal tubular acidosis are:

- Polyuria, polydipsia and dehydration

- Hypophosphatemic rickets (in children) and osteomalacia (in adults)

- Growth failure

- Acidosis

- Hypokalemia

- Hyperchloremia

Other features of the generalized proximal tubular dysfunction of the Fanconi syndrome are:

- Hypophosphatemia/hyperphosphaturia

- Glycosuria

- Proteinuria/aminoaciduria

- Hyperuricosuria

The differential diagnosis of normal anion gap acidosis is relatively short (when compared to the differential diagnosis of "acidosis"):

- Hyperalimentation

- Acetazolamide and other carbonic anhydrase inhibitors

- Renal tubular acidosis

- Diarrhea: due to a loss of bicarbonate. This is compensated by an increase in chloride concentration, thus leading to a normal anion gap, or hyperchloremic, metabolic acidosis. The pathophysiology of increased chloride concentration is the following: fluid secreted into the gut lumen contains higher amounts of Na than Cl; large losses of these fluids, particularly if volume is replaced with fluids containing equal amounts of Na and Cl, results in a decrease in the plasma Na concentration relative to the Clconcentration. This scenario can be avoided if formulations such as lactated Ringer’s solution are used instead of normal saline to replace GI losses.

- Ureteroenteric fistula - an abnormal connection (fistula) between a ureter and the gastrointestinal tract

- Pancreaticoduodenal fistula - an abnormal connection between the pancreas and duodenum

- Spironolactone

As opposed to high anion gap acidosis (which involves increased organic acid production), normal anion gap acidosis involves either increased production of chloride (hyperchloremic acidosis) or increased excretion of bicarbonate.

Inborn errors of renal tubular transport are metabolic disorders which lead to impairment in the ability of solutes, such as salts or amino acids, to be transported across the brush border of the renal tubule. This results in disruptions of renal reabsorption.

Examples of these disorders include Iminoglycinuria, renal tubular acidosis and Gitelman syndrome.

The main causes of hypokalemic acidosis are systemic disorders that can be divided into:

- Carbonic anhydrase inhibitors such as acetazolamide

- Dialysis, in the post-treatment

- Diarrhea

- Renal tubular acidosis

- Treated DKA with insulin therapy

- VIPoma

Hypouricemia is not a medical condition itself (i.e., it is benign), but it is a useful medical sign. Usually hypouricemia is due to drugs and toxic agents, sometimes it is due to diet or genetics, and rarely it is due to an underlying medical condition. When one of these causal medical conditions is present, hypouricemia is a common sign.

Hypouricemia is a level of uric acid in blood serum that is below normal. In humans, the normal range of this blood component has a lower threshold set variously in the range of 2 mg/dL to 4 mg/dL, while the upper threshold is 530 micromol/L (6 mg/dL) for women and 619 micromol/L (7 mg/dL) for men. Hypouricemia usually is benign and sometimes is a sign of a medical condition.

Symptoms are not specific, and diagnosis can be difficult unless the patient presents with clear indications for arterial blood gas sampling. Symptoms may include chest pain, palpitations, headache, altered mental status such as

severe anxiety due to hypoxia, decreased visual acuity, nausea, vomiting, abdominal pain, altered appetite and weight gain, muscle weakness, bone pain, and joint pain. Those in metabolic acidosis may exhibit deep, rapid breathing called Kussmaul respirations which is classically associated with diabetic ketoacidosis. Rapid deep breaths increase the amount of carbon dioxide exhaled, thus lowering the serum carbon dioxide levels, resulting in some degree of compensation. Overcompensation via respiratory alkalosis to form an alkalemia does not occur.

Extreme acidemia leads to neurological and cardiac complications:

- Neurological: lethargy, stupor, coma, seizures

- Cardiac: arrhythmias (ventricular tachycardia) and decreased response to epinephrine, both leading to hypotension

Physical examination occasionally reveals signs of disease, but is otherwise normal. Cranial nerve abnormalities are reported in ethylene glycol poisoning, and retinal edema can be a sign of methanol intoxication. Longstanding chronic metabolic acidosis leads to osteoporosis and can cause fractures.

In renal physiology, normal anion gap acidosis, and less precisely non-anion gap acidosis, is an acidosis that is "not" accompanied by an abnormally increased anion gap.

The most common cause of normal anion gap acidosis is diarrhea with a renal tubular acidosis being a distant second.

Metabolic acidosis is a condition that occurs when the body produces excessive quantities of acid or when the kidneys are not removing enough acid from the body. If unchecked, metabolic acidosis leads to acidemia, i.e., blood pH is low (less than 7.35) due to increased production of hydrogen ions by the body or the inability of the body to form bicarbonate (HCO) in the kidney. Its causes are diverse, and its consequences can be serious, including coma and death. Together with respiratory acidosis, it is one of the two general causes of acidemia.

Terminology :

- Acidosis refers to a process that causes a low pH in blood and tissues.

- Acidemia refers specifically to a low pH in the blood.

In most cases, acidosis occurs first for reasons explained below. Free hydrogen ions then diffuse into the blood, lowering the pH. Arterial blood gas analysis detects acidemia (pH lower than 7.35). When acidemia is present, acidosis is presumed.

Dent's disease (or Dent disease) is a rare X-linked recessive inherited condition that affects the proximal renal tubules of the kidney. It is one cause of Fanconi syndrome, and is characterized by tubular proteinuria, excess calcium in the urine, formation of calcium kidney stones, nephrocalcinosis, and chronic kidney failure.

"Dent's disease" is often used to describe an entire group of familial disorders, including X-linked recessive nephrolithiasis with kidney failure, X-linked recessive hypophosphatemic rickets, and both Japanese and idiopathic low-molecular-weight proteinuria. About 60% of patients have mutations in the "CLCN5" gene (Dent 1), which encodes a kidney-specific chloride/proton antiporter, and 15% of patients have mutations in the "OCRL1" gene (Dent 2).

Hypokalemic acidosis is a normal anion gap metabolic acidosis that has various direct and associated symptoms. Symptoms are associated with hypokalemia instead of hyperkalemia.

When acidosis is present on blood tests, the first step in determining the cause is determining the anion gap. If the anion gap is high (>12 mEq/L), there are several potential causes.

High anion gap metabolic acidosis is a form of metabolic acidosis characterized by a high anion gap (a medical value based on the concentrations of ions in a patient's serum). An anion gap is usually considered to be high if it is over 12 mEq/L.

High anion gap metabolic acidosis is caused generally by acid produced by the body. More rarely, high anion gap metabolic acidosis may be caused by ingesting methanol or overdosing on aspirin. The Delta Ratio is a formula that can be used to assess elevated anion gap metabolic acidosis and to evaluate whether mixed acid base disorder (metabolic acidosis) is present.

The list of agents that cause high anion gap metabolic acidosis is similar to but broader than the list of agents that cause a serum osmolal gap.

Fanconi syndrome or Fanconi's syndrome (, ) is a syndrome of inadequate reabsorption in the proximal renal tubules of the kidney. The syndrome can be caused by various underlying congenital or acquired diseases, by toxicity (for example, from toxic heavy metals), or by adverse drug reactions. It results in various small molecules of metabolism being passed into the urine instead of being reabsorbed from the tubular fluid (for example, glucose, amino acids, uric acid, phosphate, and bicarbonate). Fanconi syndrome affects the proximal tubules, namely, the proximal convoluted tubule (PCT), which is the first part of the tubule to process fluid after it is filtered through the glomerulus, and the proximal straight tubule (pars recta), which leads to the descending limb of the loop of Henle.

Different forms of Fanconi syndrome can affect different functions of the proximal tubule, and result in different complications. The loss of bicarbonate results in type 2 or proximal renal tubular acidosis. The loss of phosphate results in the bone diseases rickets and osteomalacia (even with adequate vitamin D and calcium levels), because phosphate is necessary for bone development in children and even for ongoing bone metabolism in adults.

Classical signs of uremia are: progressive weakness and easy fatigue, loss of appetite due to nausea and vomiting, muscle atrophy, tremors, abnormal mental function, frequent shallow respiration and metabolic acidosis. Without intervention via dialysis or kidney transplant, uremia due to renal failure will progress and cause stupor, coma and death. Because uremia is mostly a consequence of kidney failure, its signs and symptoms often occur concomitantly with other signs and symptoms of kidney failure. Below is a table showing more of the principal signs and symptoms of uremia.

Glomerular filtration rate (GFR) measures the amount of plasma being filtered through the kidneys. As the GFR decreases, the prognosis worsens. Some of the effects can be reversed with dialysis. See below for a chart on GFR rates and their effects.

Though this condition is usually asymptomatic, if symptoms are present they are usually related to the causative process, (e.g. hypercalcemia). Some of the sympotoms that can happen are blood in the urine, fever and chills, nausea and vomiting, severe pain in the belly area, flanks of the back, groin, or testicles.

These include renal colic, polyuria and polydipsia:

- Renal colic is usually caused by pre-existing nephrolithiasis, as may occur in patients with chronic hypercalciuria. Less commonly, it can result from calcified bodies moving into the calyceal system.

- Nocturia, polyuria, and polydipsia from reduced urinary concentrating capacity (i.e. nephrogenic diabetes insipidus) as can be seen in hypercalcemia, medullary nephrocalcinosis of any cause, or in children with Bartter syndrome in whom essential tubular salt reabsorption is compromised.

There are several causes of nephrocalcinosis that are typically acute and present only with renal failure. These include tumor lysis syndrome, acute phosphate nephropathy, and occasional cases of enteric hyperoxaluria.

Causes include:

The newest mnemonic was proposed in "The Lancet" reflecting current causes of anion gap metabolic acidosis:

- G — glycols (ethylene glycol & propylene glycol)

- O — oxoproline, a metabolite of paracetamol

- L — L-lactate, the chemical responsible for lactic acidosis

- D — D-lactate

- M — methanol

- A — aspirin

- R — renal failure

- K — ketoacidosis, ketones generated from starvation, alcohol, and diabetic ketoacidosis

The mnemonic MUDPILES is commonly used to remember the causes of increased anion gap metabolic acidosis.

- M — Methanol

- U — Uremia (chronic kidney failure)

- D — Diabetic ketoacidosis

- P — Paracetamol, Propylene glycol (used as an inactive stabilizer in many medications; historically, the "P" also stood for Paraldehyde, though this substance is not commonly used today)

- I — Infection, Iron, Isoniazid (which can cause lactic acidosis in overdose), Inborn errors of metabolism (an especially important consideration in pediatric patients)

- L — Lactic acidosis

- E — Ethylene glycol (Note: Ethanol is sometimes included in this mnemonic as well, although the acidosis caused by ethanol is actually primarily due to the increased production of lactic acid found in such intoxication.)

- S — Salicylates

Another frequently used mnemonic is KARMEL.

- K — Ketoacidosis

- A — aspirin

- R — Renal failure

- M — Methanol

- E — Ethylene glycol

- L — Lactic acidosis

Another frequently used mnemonic is KULT.

- K — Ketoacidosis (DKA, AKA)

- U — Uremia

- L — Lactic acidosis

- T — Toxins (Ethylene glycol, methanol, as well as drugs, such as aspirin, Metformin)

The preferred mnemonic of D. Robert Dufour, the chief of the Pathology and Laboratory Medicine Service, Veterans Affairs Medical Center, is DUMPSALE, which omits the I of MUDPILES as the proposed values of *I* are exceedingly rare in clinical practice.

- D — Diabetic ketoacidosis

- U — Uremia

- M — Methanol

- P — Paraldehyde

- S — Salicylates

- A — Alcoholic ketoacidosis

- L — Lactic acidosis

- E — Ethylene Glycol

The mnemonic for the [rare, in comparison] toxins is ACE GIFTs: Aspirin, Cyanide, Ethanolic ketosis, Glycols [ ethylene and propylene ], Isoniazid, Ferrous iron, Toluene. Most of these cause a lactic acidosis.