Renal impairment is characterised by the reduced ability of the kidneys to excrete waste and maintain the electrolyte balance. This encompasses both acute kidney injury (AKI) and chronic kidney disease (CKD). CKD is very common, with 8.5% of the population having baseline impairment of kidney function (stage 3 - 5 chronic kidney disease, defined by an eGFR of <60 ml/min/1.73m2) . This has usually occurred over a period of years and is associated with diseases such as hypertension, cardiovascular disorders or diabetes . AKI affects between 13 and 18% of all people admitted to hospital and the severity of the AKI is defined according to the amount by which serum creatinine has increased within a 48-hour period . It is usually reversible but is associated with a major increased mortality risk in those affected . In patients who present with AKI of unknown cause the underlying pathology may be multiple myeloma (MM) and they should be rapidly screened for monoclonal gammopathy (Section 27.2).
In patients with renal impairment, the reticuloendothelial system becomes the dominant mechanism for the clearance of FLCs and other proteins from the blood. With decreased renal clearance, the relative concentrations of κ and λ sFLCs become increasingly influenced by production rates, leading to minor increases in the sFLC ratio in the absence of monoclonal gammopathy . Application of a modified renal reference interval for patients with renal impairment may increase the specificity of the κ/λ sFLC ratio for detecting monoclonal FLC production (Section 6.3). If there is complete renal failure, the serum half-life of both FLCs will be the same and may be prolonged to 2 - 3 days, resulting in significant increases in serum concentration for both light chains.