Acute Kidney Injury (AKI) vs Chronic Kidney Disease (CKD)

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Acute kidney injury (AKI)

An acute kidney injury (AKI) is caused by a rapid deterioration in kidney function.

The pathophysiology of AKI is separated into three main causes:

Pre-renal: decreased blood supply resulting in decreased GFR
Renal: damage to the nephron impairing the reabsorption capacity
Post-renal: increased hydrostatic pressure resulting in reduced GFR

AKI is clinically detected when a patient presents with oliguria or anuria; often in the context of hospital admission or risk factors for AKI (e.g. underlying chronic disease, history of AKI, use of nephrotoxic drugs).

The management of AKI depends on the underlying cause. All patients should have their existing medications reviewed with removal of nephrotoxic medications.

AKI can be a significant cause of morbidity and mortality; however, prompt recognition and management can help to prevent progression and long-term damage.

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Chronic kidney disease (CKD)

Chronic kidney disease (CKD) is defined as abnormal kidney function or structure present for greater than three months.

The most common causes of CKD are diabetes and vascular disease; CKD represents the end-stage for any cause of severe and/or long-standing kidney injury.

CKD is primarily asymptomatic, and symptoms usually only start developing when it is advanced.

Symptoms may include fatigue, nausea and vomiting, abnormal urine output and fluid overload. The general management of CKD involves a combination of lifestyle modifications, medications, and regular monitoring. Renal replacement therapy is an important aspect of the treatment of end-stage CKD.

Acute on Chronic Kidney Disease

‘Acute on chronic’ renal disease is characterised by the acute deterioration of renal function superimposed on pre-existing CKD. It should be suspected when a patient with known CKD experiences a sudden spike in serum creatinine above their established baseline.

Summary table

	Acute kidney injury	Chronic kidney disease
Onset	Rapid decrease of renal function over hours to days	Gradual or progressive decrease of renal function over months to years
Clinical definitions	The kidney disease improving global outcomes (KDIGO) classification tool confirms an AKI with any of the following present:¹ Urine output less than 0.5ml/kg/hr for 6 hours Serum creatinine increase 1.5x the baseline over 7 days Serum creatinine increase by 0.3mg/dL in 48 hours	Abnormal kidney function or structure present for greater than three months, with subsequent implications for health.² Further classified according to eGFR and proteinuria.
Aetiology	Pre-renal injury (e.g. absolute hypovolemia, low effective arterial blood volume, renal artery stenosis) Intra-renal injury (e.g. acute tubular necrosis, acute interstitial nephritis, glomerular disease, intra-tubular obstruction) Post-renal (e.g. nephrolithiasis, benign prostatic hypertrophy, stricture, ovarian tumour)	Diabetes, vascular disease Hereditary kidney disease (e.g. PCOS, Alport syndrome) Obstructive uropathy
Clinical features	Vary depending on the underlying aetiology – fluid overload, hypotension, metabolic acidosis Decreased production of urine	Primarily asymptomatic; may have hypertension, haematuria and/or proteinuria
Diagnosis	Rapidly increasing creatinine values or decreasing urine output eGFR is used	History indicating progressive derangement of creatinine and eGFR
Haemoglobin	Normal (rarely low, unless in the case of bleeding)	Low; chronic normocytic anaemia is common due to erythropoietin deficiency
Calcium and parathyroid hormone	Normal parathyroid hormone Normal calcium	High parathyroid hormone Low or normal calcium
Reversible?	Commonly reversible	Irreversible
Ultrasound appearance of kidneys	Typically normal; may show hydronephrosis in the case of obstruction	Asymmetrical kidneys, shrunken or enlarged kidneys

References

KDIGO. 2012 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline for Acute Kidney Injury (AKI). (2012). Available from: [LINK]
NICE CKS. Chronic Kidney Disease – Definition. 2021. Available from: [LINK]