Dynamic single-parameter: AK

The trends of blood results, i.e. their rise or fall, have always been extremely valuable to clinicians. A recent and highly publicised interpretation of a very specific dynamic change in just one specific blood result (creatinine) is that of AKI.82

AKI is an abrupt impairment in kidney function that results in a rise in serum creatinine concentration or a fall in urine output. AKI is a broad clinical syndrome that encompasses a number of aetiologies, including but not limited to kidney diseases (e.g. acute interstitial nephritis; acute glomerular and vasculitic renal diseases; ischaemia, toxic injury), extra-renal pathology (for example, pre-renal azotaemia, acute post-renal obstructive nephropathy, sepsis). More than one of these conditions may coexist in the same patient. In 2012, to harmonise the detection and treatment of AKI, a rise in patient’s serum creatinine and a fall in their urine output measures were used by the Kidney Disease: Improving Global Outcomes (KDIGO) group, to standardise definitions of its presence and stage of severity (stages 1–3).83

One in every five hospitalised adults (21%) suffer AKI84, worldwide; with a prevalence of 14% reported amongst UK hospital admissions.79 _{AKI is also associated with increased risk of death}85_{, prolonged}

hospitalisation86_{, requirement for renal replacement therapy}87_{, or the development of chronic kidney}

disease.88 _{The associated health care costs of AKI exceed £1 billion per year in the UK.}79 _{Over 50% of}

AKI-associated morbidity and mortality may be preventable with early detection and appropriate intervention.5 _{A more systematic approach that does not rely on any one individual checking or acting}

on results, rather a process that used existing data to alert health care staff that a patient is at high risk of an poor outcome based on their results is now achievable, given the way we store and report blood test results.

In response, initiatives throughout the world have attempted to promote AKI recognition and encourage timely interventions to hasten its resolution.82 _{In 2015, the National Health Service of}

KDIGO, Table 1.1) in hospital laboratory information-management systems (NHSE-AKI algorithm, Figure 1.8). The NHSE-AKI algorithm compares the current creatinine result of a patient with their previous results, to determine whether a significant rise has occurred. Specifically, the current result is compared to a ‘baseline creatinine’ value, which is calculated as either the patient’s minimum creatinine result in the previous seven days, or the median of all their creatinine results in the preceding 8–365 days, whichever is lower.

Table 1.1: Kidney Disease Improving Global Outcomes (KDIGO): Staging of AKI

Stage Serum Creatinine Urine output

1 1.5–1.9 times baseline or >0.3 mg/dl (>26.5 mol/l) increase < 0.5ml/kg/hr for 6- 12 hours

2 2.0–2.9 times baseline < 0.5 ml/kg/hr for > 12 hours

3

3.0 times baseline or

Increase in serum creatinine to >4.0 mg/dl (>353.6 mol/l) or

Initiation of renal replacement therapy or

In patients <18 years, decrease in eGFR to <35 ml/min per 1.73 m2

< 0.3 ml/kg/hr for > 24 hours

or

Anuria for > 12 hours

The NHSE-AKI algorithm is intended to alert clinicians to potential AKI cases and their likely severity stage, and thus identify those at risk of subsequent AEs, such as death or renal replacement therapy (Drrt).89 Clinical assessment following such an AKI alert may lead to an escalation of intervention according to the AKI stage (Figure 1.9). Thus, although not explicitly labelled as such, the NHSE-AKI algorithm could be regarded as the afferent limb of a ‘rapid response system’ (RRS), where the efferent limb ‘rapid response team’ (RRT) includes a nephrologist.

However, whilst clinicians may consider more severe AKI stages to be more dangerous (and worthy of prioritisation of care), the degree to which this is correct is unclear. Patient heterogeneity or clinical state (e.g. the presence of dehydration or of co-morbidities) might influence the degree of risk within any one AKI stage, or across stages. Likewise, multiple trigger routes can lead to the same AKI stage (Figure 1.8), but might be associated with different outcomes. None of these issues have been sufficiently evaluated on a large multisite dataset, and thus we have yet to establish the benefit of implementing an existing AKI algorithm, which does not account for all of these factors, as the afferent limb of a referral system.

Figure 1.8: The NHS England Acute Kidney Injury Algorithm (NHSE-AKI algorithm)

Serum creatinine result exists?

Previous result Within 0 – 365 days? Index creatinine value

Defined as C1 If Result within 0 – 7 days Then: If Result within 8 – 365 days Then: Find lowest value Define as RV1 Calculate RV ratio C1 / RV1 Find MEDIAN of results Define as RV2 Calculate RV ratio C1 / RV2 Is higher RV ratio ≥ 3.0? Is higher RV ratio ≥ 2.0 and < 3.0? Is higher RV ratio ≥ 1.5 and < 2.0? ALERT! ?AKI 3 Alert! ?AKI 2 ALERT! ?AKI 1 Is higher RV ratio ≥ 1.5?

Has change occurred Within 48hrs?

Is D > 26 μmol/L?

Report without alert Report without alert. Send to authorisation Q If creatinine has Increased > 26 μmol/L In < 7 days. Consider requesting repeat If CKD unlikely.

< RI? Flag low

Within RI? No flag

Flag High ?AKI ?CKD

Suggest Repeat

Algorithm for detecting Acute Kidney Injury (AKI) based on serum creatinine changes with time

This algorithm relates to the NHS England patient safety alert: NHS/PSA/D/2014/010

RI =Population Reference Interval (Age and sex related if available)

RV = Reference value. Defined as: the creatinine value with which an index

creatinine value is compared

D = difference between current and lowest previous result within 48hrs YES NO YES YES NO NO NO YES YES YES YES YES NO NO NO NO ULRI = upper limit of reference interval

Is age < 18 years? Serum creatinine _{> x3 ULRI?}

Serum creatinine > 354 μmol/L? YES YES YES YES NO NO NO

Figure 1.9: Stage-based management of AKI

Shading of boxes indicates priority of action: solid shading indicates actions that are equally appropriate at all stages whereas graded shading indicates increasing priority as intensity increases. AKI: acute kidney injury; ICU: intensive care unit.