Renal Tubular Acidosis

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Last updated: September 17, 2026Bookmark

Table Of Contents

Overview
Type 1: Distal RTA
Type 2: Proximal RTA
Type 3 RTA
Type 4 RTA

Overview

Renal tubular acidosis is a non-anion gap hyperchloremic metabolic acidosis that is caused by impaired renal HCO3- handling or increased H+ excretion.

Summary of renal tubular acidosis (RTA)

Classification	Causes	Pathophysiology	K+	Urine pH
Type 1 (distal)	Sjogren syndrome, SLE, chronic obstruction, amphotericin B, lithium	Reduced H+ secretion in the distal nephron causes metabolic acidosis and an inability to acidify urine.	Low	> 5.5 despite acidosis
Type 2 (proximal)	Monoclonal gammopathy, Fanconi syndrome, acetazolamide, topiramate, tenofovir, ofosfamide	Reduced HCO3- absorption in the proximal tubules	Low	Variable; < 5.5 once serum HCO3- falls
Type 3	Very rare; carbonic anhydrase II deficiency	Combined proximal and distal defects	–	–
Type 4	Diabetic nephropaty, ACEi/ARB, K+ sparing diuretics, NSAIDs, Heparin	Reduced aldosterone or aldosterone resistance	High	< 5.5

Investigations
- Blood gas analysis to confirm metabolic acidosis
- Serum K+
  - Hypokalemia in Type 1 and Type 2 RTA
  - Hyperkalemia in Type 4 RTA
- Urine pH
  - 5.5 in Type 1 or 2 RTA
  - < 5.5 in Type 4 RTA
- Urine anion gap (UAG)
  - Positive UAG suggests reduced NH4+ excretion and supports RTA
- Urinalysis to rule out UTI with urease-producing organisms that can elevate urine pH
Treatment
- Treat the underlying cause
- Bicarbonate 1 – 2 mEq/kg/day to correct chronic acidosis
  - A higher dose of bicarbonate is required in Type 2 since it is continuously lost in urine
- Potassium citrate for hypokalemia, nephrolithiasis, or nephrocalcinosis
- Correct hypophosphataemia if present
- Correct vitamin D deficiency if present
- For type 4 RTA:
  - Dietary K+ restriction
  - Loop diuretics or thiazide diuretics
  - Fludrocortisone for aldosterone deficiency (note that it can worsen hypertension, oedema, and heart failure)

Type 1: Distal RTA

Type 1 RTA occurs when there is reduced secretion of H+ in the distal tubules. This makes urine more alkaline, hence the urine pH remains > 5.5. despite a metabolic acidosis.

Common causes
- Autoimmune disease
  - Sjogren syndrome
  - SLE
- Drugs
  - Amphotericin B
  - Lithium
Associated conditions
- Hypokalemia
- Hypercalciuria
- Hypocitraturia
- Nephrocalcinosis or calcium phosphate stones
- Osteomalacia and rickets

Type 2: Proximal RTA

Type 2 RTA occurs when there is reduced absorption of HCO3- in the proximal tubules. Bicarbonate is excreted in urine leading to metabolic acidosis. The urine pH is variable – it can become acidic once plasma HCO3- falls below the reduced reasborptive threshold.

Associated conditions
- Fanconi syndrome – glycosuria, hypophosphataemia, hypouricaemia and other proximal tubular losses
- Hypokalemia due to increased distal Na+/H2O deliver and K+ loss
- Monoclonal gammopathy
- Drugs
  - Acetazolamide
  - Topiramate
  - Tenofovir
  - Ofosfamide

Type 3 RTA

Type 3 RTA has combined proximal and distal defects. It is very rare and commonly associated with carbonic anhydrase II deficiency

Type 4 RTA

Type 4 RTA is caused by hypoaldosteronism which leads to a hyperkalemic metabolic acidosis. Reduced aldosterone decreases K+ excretion, NH3 generation, NH4+ buffering, and H+ excretion. Urine pH is usually acidic (< 5.5) since core pathophysiology is reduced NH3 availability rather than complete failure of distal H+ secretion.

Common causes
- Hyporeninemic hypoaldosteronism
  - Diabetic nephropathy
- Drugs
  - ACEi/ARB
  - K+ sparing diuretics
  - NSAIDs
  - Heparin

Reference Intervals ›

Biochemistry

ACTH	P: <80 ng/L
ALT	P: 5–35 U/L
Albumin	P: 35–50 g/L
Aldosterone	P: 100–500 pmol/L
Alk. phosphatase	P: 30–130 U/L
α-Amylase	P: 0–180 IU/dL
α-Fetoprotein	S: <10 kU/L
Angiotensin II	P: 5–35 pmol/L
ADH	P: 0.9–4.6 pmol/L
AST	P: 5–35 U/L
Bicarbonate	P: 24–30 mmol/L
Bilirubin	P: 3–17 μmol/L
BNP	P: <50 ng/L
CRP	P: <10 mg/L
Calcitonin	P: <0.1 mcg/L
Calcium (ionized)	P: 1.0–1.25 mmol/L
Calcium (total)	P: 2.12–2.60 mmol/L
Chloride	P: 95–105 mmol/L
Cholesterol	P: <5.0 mmol/L
VLDL	P: 0.128–0.645 mmol/L
LDL	P: <2.0 mmol/L
HDL	P: 0.9–1.93 mmol/L
Cortisol AM	P: 450–700 nmol/L
Cortisol Midnight	P: 80–280 nmol/L
CK ♂	P: 25–195 U/L
CK ♀	P: 25–170 U/L
Creatinine	P: 70–100 μmol/L
Ferritin	P: 12–200 mcg/L
Folate	S: 2.1 mcg/L
FSH	P: 2–8 U/L ♂; >25 menopause
GGT ♂	P: 11–51 U/L
GGT ♀	P: 7–33 U/L
Glucose (fasting)	P: 3.5–5.5 mmol/L
Growth hormone	P: <20 mu/L
HbA1C (DCCT)	B: 4–6%
HbA1C (IFCC)	B: 20–42 mmol/mol
Iron ♂	S: 14–31 μmol/L
Iron ♀	S: 11–30 μmol/L
Lactate (venous)	P: 0.6–2.4 mmol/L
Lactate (arterial)	P: 0.6–1.8 mmol/L
LDH	P: 70–250 U/L
LH	P: 3–16 U/L
Magnesium	P: 0.75–1.05 mmol/L
Osmolality	P: 278–305 mosmol/kg
PTH	P: 0.8–8.5 pmol/L
Potassium	P: 3.5–5.3 mmol/L
Prolactin ♂	P: <450 U/L
Prolactin ♀	P: <600 U/L
PSA	P: 0–4 mcg/mL
Protein (total)	P: 60–80 g/L
Red cell folate	B: 0.36–1.44 μmol/L
Renin (erect)	P: 2.8–4.5 pmol/mL/h
Renin (recumbent)	P: 1.1–2.7 pmol/mL/h
Sodium	P: 135–145 mmol/L
TBG	P: 7–17 mg/L
TSH	P: 0.5–4.2 mU/L
T4	P: 70–140 nmol/L
Free T4	P: 9–22 pmol/L
TIBC	S: 54–75 μmol/L
Triglycerides	P: 0.50–2.3 mmol/L
T3	P: 1.2–3.0 nmol/L
Troponin T	P: <0.1 mcg/L
Urate ♂	P: 210–480 μmol/L
Urate ♀	P: 150–390 μmol/L
Urea	P: 2.5–6.7 mmol/L
Vitamin B12	S: 0.13–0.68 nmol/L
Vitamin D	S: 50 nmol/L

Arterial Blood Gases

pH	7.35–7.45
PaCO₂	4.7–6.0 kPa
PaO₂	>10.6 kPa
Base excess	±2 mmol/L

Urine

Cortisol (free)	<280 nmol/24h
Hydroxyindole acetic acid	16–73 μmol/24h
Hydroxymethylmandelic acid	16–48 μmol/24h
Metanephrines	0.03–0.69 μmol/mmol cr.
Osmolality	350–1000 mosmol/kg
17-Oxogenic steroids ♂	28–30 μmol/24h
17-Oxogenic steroids ♀	21–66 μmol/24h
17-Oxosteroids ♂	17–76 μmol/24h
17-Oxosteroids ♀	14–59 μmol/24h
Phosphate (inorganic)	15–50 mmol/24h
Potassium	14–120 mmol/24h
Protein	<150 mg/24h
Protein/creatinine ratio	<3 mg/mmol
Sodium	100–250 mmol/24h

Haematology

WCC	4.0–11.0 ×10⁹/L
RBC ♂	4.5–6.5 ×10¹²/L
RBC ♀	3.9–5.6 ×10¹²/L
Hb ♂	130–180 g/L
Hb ♀	115–160 g/L
PCV ♂	0.4–0.54 L/L
PCV ♀	0.37–0.47 L/L
MCV	76–96 fL
MCH	27–32 pg
MCHC	300–360 g/L
RDW	11.6–14.6%
Neutrophils	2.0–7.5 ×10⁹/L (40–75%)
Lymphocytes	1.0–4.5 ×10⁹/L (20–45%)
Eosinophils	0.04–0.44 ×10⁹/L (1–6%)
Basophils	0–0.10 ×10⁹/L (0–1%)
Monocytes	0.2–0.8 ×10⁹/L (2–10%)
Platelets	150–400 ×10⁹/L
Reticulocytes	0.8–2.0% / 25–100 ×10⁹/L
Prothrombin time	10–14 s
APTT	35–45 s

Paediatric

Pulse Rate (bpm)
Neonate	140–160
Infant <1yr	120–140
1–5 years	110–130
5–12 years	80–120
>12 years	70–100
Respiratory Rate (tachypnoea)
0–2 months	≥60/min
2–12 months	≥50/min
1–5 years	≥40/min
>5 years	≥30/min
Blood Pressure (mmHg)
Term	65/45
1 year	75/50
4 years	85/60
8 years	95/65
10 years	100/70
Weight Formulas
3–12 months	(a + 9)/2 kg
1–6 years	2a + 8 kg
>6 years	(7a − 5)/2 kg
Haemoglobin (g/dL)
Term newborn	13–20
1 month	11–18
2 months	10–15
1–2 years	10–13
>2 years	11–14
MUAC (6 months–5 years)
Obese	>17.5 cm
Normal	13.5–17.4 cm
At risk	12.5–13.4 cm
Moderate malnutrition	11.5–12.4 cm
Severe malnutrition	<11.5 cm
Developmental Milestones
Social smile	1.5 months
Head control	4 months
Sits unsupported	7 months
Crawls	10 months
Stands unsupported	10–12 months
Walks	12–13 months
Talks	18 months
CSF WBC (/mm³)
Term newborn	0–25
>2 weeks	0–5

Calculator ›

Overview

Type 1: Distal RTA

Type 2: Proximal RTA

Type 3 RTA

Type 4 RTA

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