KidneyFish
Nephromaths
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Disclaimer
Acknowledgements
I Introduction
1
Introduction
1.1
Work in progress
1.2
What this book is - and what it is not
1.3
How to use this book
2
Basic Concepts
2.1
Validity & assumptions
2.2
General principles
2.2.1
Balance
2.2.2
Testing during stress & “normal ranges”
2.2.3
Renal clearance & fractional excretion
2.2.4
Tmax
2.2.5
Osmolarity, osmolality & tonicity
2.2.6
Gaps
3
General approach to a patient with electrolyte disturbance
3.1
Vomiting & diarrhoea
3.1.1
Electrolyte content of body fluids
3.1.2
Vomiting
3.1.3
Quantitative assessment after vomiting
3.1.4
Diarrhoea
3.2
Drugs
3.3
IV fluids & electrolyte supplements
3.4
Diet
3.5
Basic set of investigations
II Acid-base
4
Acid-base & chloride
4.1
Acid-base homeostasis
4.2
pH
4.3
Adaptation
4.4
Renal control of acid-base homeostasis
4.4.1
Normal renal response to chronic acidosis
4.4.2
Citrate metabolism in acidosis
4.4.3
Renal response to alkalosis
5
Metabolic acidosis
5.1
Serum anion & osmolar gaps
5.2
Investigations in HCMA
5.2.1
Urine pH
5.2.2
Urine anion gap, osmolar gap, ammonium
5.3
Causes of a metabolic acidosis
5.3.1
Approach to metabolic acidosis
6
Metabolic alkalosis (& chloride homeostasis)
6.1
Causes of a metabolic alkalosis
6.1.1
Specific syndromes and their mechanisms
6.2
Chloride
6.2.1
Chloride-depletion alkalosis
7
Respiratory acid-base disorders
7.1
Classification of respiratory acid-base disorders
7.2
A-a gradient
7.2.1
Alveolar gas equation
7.2.2
Explanation
7.2.3
Interpretation
III Water and sodium
8
Water and sodium
8.1
Total body water
8.2
Plasma sodium
8.3
Renal water excretion
8.4
Urine osmolality
9
Hyponatraemia
9.1
Drug causes of hyponatraemia
9.2
Correction for hyperglycaemia
9.3
Urine sodium
9.3.1
FE
Na
9.3.2
FE
urate
as an alternative index of volume status
9.4
Free water clearance
9.4.1
Calculating free water clearance
9.4.2
Clinical utility of free water clearance
9.4.3
Urine flow rate in hyponatraemia
9.5
SIAD
9.5.1
Diagnosis
9.5.2
Subtypes
9.5.3
Treatment
10
Hypernatraemia
10.1
Causes of hypernatraemia
10.2
Diagnosis in hypernatraemia
10.3
Treatment of hypernatraemia
11
Polyuria
11.1
Causes
11.2
Investigation of polyuria
11.3
Uses for copeptin testing
11.3.1
Assay details
11.3.2
Polyuria-polydipsia (hypotonic polyuria)
11.3.3
Hypernatraemia
11.3.4
Hyponatraemia
IV Potassium
12
Potassium
12.1
Quantification
12.1.1
Interpretation
12.2
TTKG
Assumptions & pre-requisites
Interpretation
13
Hypokalaemia
13.1
Causes of hypokalaemia
13.2
Causes of K loss
13.3
Diagnostic approach
13.4
Vomiting
13.5
Non-reasbsorbable anions
13.6
Hypokalaemic periodic paralysis
14
Hyperkalaemia
14.1
Causes of hyperkalaemia
14.2
Causes of spurious hyper- and hypokalaemia
V Phosphate, Calcium, Magnesium
15
Phosphate
15.1
Urinary phosphate
15.1.1
General approach
15.1.2
Measuring urinary phosphate and calculating TmP/GFR
15.1.3
Reference ranges
15.2
Hypophosphataemia
15.2.1
Consequences
15.2.2
Causes of hypophosphataemia
15.2.3
Notes on specific causes
16
Calcium
16.1
Investigations in hypercalcaemia:
16.2
Urine calcium
16.3
Interpreting the results
16.3.1
Unit conversions
16.3.2
Normal calcium excretion:
16.3.3
Hypercalciuria (e.g. in hyperPTH, other causes of hypercalcaemia, RTA):
16.3.4
Hypocalciuria (e.g. FHH, Gitelman):
17
Magnesium
17.1
Mg homeostasis
17.2
Hypomagnesaemia
17.2.1
Consequences
17.2.2
Differential diagnosis of hypomagesaemia
17.2.3
Notes on specific causes
17.3
Investigations
VI Tubulopathies
18
Tubulopathies
18.1
Inherited
18.1.1
Notes on some of the inherited tubulopathies
18.2
Acquired
18.3
Tubulopathy syndromes
18.3.1
Interpretation of these electrolyte syndromes
18.4
Diagnostic approach in suspected tubulopathy
18.4.1
Fractional excretions
18.4.2
Specialised testing
18.5
Sjogren syndrome
18.6
Lithium-associated tubulopathy
18.6.1
Pathogenesis
18.6.2
Polyuria
18.6.3
TIN
18.6.4
Podocytopathy
18.7
Salt-wasting tubulopathies
19
Renal tubular acidosis
19.1
Classification of RTA
19.1.1
Pathogenesis of hypokalaemic RTA
19.1.2
Pathogenesis of hyperkalaemic RTA
19.1.3
Associations
19.1.4
Investigation of suspected RTA
19.1.5
Causes
19.2
Fanconi syndrome
19.3
Management of adult dRTA
Appendices
A
Appendix 1 - notation & abbreviations
A.1
Notation
A.2
Glossary of abbreviations
B
Appendix 2 - rules of thumb
B.1
pH and [H
+
]
B.2
Urine specific gravity and UOsm
C
Appendix 3 - what’s the mechanism?
C.1
Mechanisms in dRTA (see ESPN clinical practice points, NDT 2021):
C.2
Mechanisms in salt-wasting tubulopathy (See Dutta & Layton, AJP Renal 2024 – a modelling study)
D
Appendix 4 - references
Published with bookdown
Nephromaths
Nephromaths
Robert W Hunter
2026-04-30
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