24th June 2024

Chronic Kidney Disease & Electrolyte Imbalance

Chronic kidney disease

Background

Chronic kidney disease (CKD) is defined by abnormalities in the function or structure of the kidney which is present for more than 3 months. This can also be defined as a glomerular filtration rate (GFR) of <60mL/minute/1.73m² or abnormal kidney structure or albuminuria. GFR and albuminuria are used to stage CKD. The former is based on age, sex, height and serum creatinine and cystatin C.  The most common causes of CKD are diabetes, hypertension, and glomerulonephritis. Complications are progressive, based on the level of CKD, and can include hypertension, anaemia, electrolyte disturbance, and end-stage renal failure.

Diagnosis

CKD is often asymptomatic, particularly in the early stages. Symptoms tend to occur in association with complications.  The most common of those are hormonal and metabolic complications such as anaemia, hyperparathyroidism and risks associated with systemic drug toxicity, cardiovascular disease, and infection. End-stage renal failure (ESRF) generally refers to CKD requiring dialysis or transplantation.

Staging

Staging is used to guide management and predict the risk of progression to complications. This is then used as a guide to inform appropriate monitoring and treatment strategy. GFR is divided into 6 categories for the purpose of staging, as highlighted in Table 1. G3 has been divided into 3a and 3b owing to evidence which demonstrated increasing mortality and adverse kidney outcomes associated with a continuous decrease in GFR. Albuminuria is also used in staging. This is again divided into stages, with none, microalbuminuria, (now referred to as ‘moderately increased’) and macroalbuminuria, (now referred to as severely increased/nephrotic range). Albuminuria is significant due to a correlated risk of progression to ESRF and mortality independent of GFR.

Management

Most patients with evidence of CKD are managed by a nephrologist, with referral once GFR is sustained below 30 mL/minute/1.73 m². In addition, evidence of the sequelae of CKD should also prompt referral, for instance, refractory hypertension, persistent electrolyte abnormalities, as well as consistent evidence of albuminuria. Management is often focused on slowing the progression of disease. Hypertension management tends to be more robust in those with CKD and tends to include the use of an ACEi or ARB. Diabetic management focuses on reducing HbA1c, whilst lipid management is also important. Avoidance of nephrotoxic medications also plays a part. Renal replacement therapy is considered for appropriate patients once GFR is 5-10 mL/minute/1.73 m²

References

• Denker B, Aird W. Overview of Chronic Kidney Disease in Adults. In DynaMed, EBSCO Information Services. Accessed September 27, 2023. https://www.dynamed.com/condition/overview-of-chronic-kidney-disease-ckd-in-adults/about
• Levey A, Inker L, Curhan G, Forman J. Definition and staging of chronic kidney disease in adults. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. Accessed September 27, 2023. https://pro.uptodatefree.ir/show/16406

Electrolyte imbalance

Closely linked to renal function, electrolyte balance is vital to normal physiology. The management of electrolytes clinically can quickly become complicated, particularly in the context of an acutely unwell patient with multi-morbidity and polypharmacy.

Sodium

Sodium is vital in maintaining extracellular fluid volume and membrane potential regulation. Regulation occurs in the kidneys where the majority of reabsorption takes place in the proximal convoluted tubule. Owing to the isotonic nature of reabsorption at this point in the nephron, water is also reabsorbed here. Further sodium reabsorption occurs in the distal ascending portion of the loop of Henle, with only 5%-10% of reabsorption taking place in the distal convoluted tubule and cortical and medullary collecting ducts. Nevertheless, the reabsorption along the distal nephron remains vital and highly regulated.

Potassium

With its haemostasis closely linked to sodium, potassium is the vital intracellular ion. Filtration occurs in the glomerulus, with reabsorption in the proximal convoluted tubule and thick ascending loop of Henle. Aldosterone increases its secretion.

Calcium

Diet is the predominant source of this predominantly extracellular cation. It is highly regulated owing to its role in skeletal mineralisation, muscle contraction and neurological transmission, as well as vascular haemostasis. Absorption in the intestine is primarily controlled by 1,23-dihydroxy vitamin D3 (the active form of vitamin D). Parathyroid hormone regulates its secretion in the distal tubule of the kidney and calcitonin reduces plasma levels through its action on bones.

Bicarbonate

Acid-base balance is regulated by the kidneys and drives bicarbonate levels. Filtered bicarbonate is reabsorbed by kidneys, whilst diarrhoea results in its loss. Renal disease will often result in an imbalance and, therefore, excess bicarbonate levels.

Phosphate

Eighty-five percent of total body phosphate is found in bones and teeth as hydroxyapatite, with soft tissue containing the remaining 15%. It is regulated by Vitamin D3, parathyroid hormone and calcitonin, in conjunction with calcium, with excretion primarily by kidneys. Imbalance is often a result of either poor dietary intake, gastrointestinal disorders or defective renal excretion.

References

• Shrimanker I, Bhattarai S. Electrolytes. 2023 Jul 24. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan–. PMID: 31082167
• Palmer LG, Schnermann J. Integrated control of Na transport along the nephron. Clin J Am Soc Nephrol. 2015 Apr 7;10(4):676-87. doi: 10.2215/CJN.12391213. Epub 2014 Aug 6. PMID: 25098598; PMCID: PMC4386267