Diagnosis and investigations in renal failure

The clinician must complete three tasks when diagnosing a new case of chronic renal failure:

• the renal failure must be demonstrated to be long-standing and not due to an acute and reversible renal insult
  
  
• the aetiology of the renal damage should be determined
  
  
• any reversible factors should be identified and addressed

Investigations:

• blood tests - FBC - normochromic normocytic anaemia; ESR; U+Es (increased urea and increased creatinine); eGFR; glucose (check for DM); urate; bone profile - reduced calcium, increased phosphate, increased alkaline phosphatase (renal osteodystrophy); increased parathyroid hormone (hyperparathyroidism)
• urine tests - MSU; creatinine clearance; 24 hour urinary protein
  • there is no need to collect 24 h urine samples to measure creatinine clearance in primary care because the estimated GFR can be calculated (1)
  • there is no need to perform 24 h urine collections for the quantitation of proteinuria in primary care because urine protein:creatinine ratio can be used to assess proteinuria (1)
• renal imaging - ultrasound - assess renal size and exclude obstruction; renal size generally small in chronic renal failure but normal or large renal size may be seen in polycystic kidney disease, diabetes mellitus, asymmetrical renal vascular disease, myeloma, amyloidosis, systemic sclerosis; other investigations such as IVU, DTPA scan should be considered
• chest X-ray
• bone X-rays - may reveal renal osteodystrophy
• renal biopsy - this investigation may be undertaken e.g. in patients with chronic renal failure and normal sized kidneys

NICE suggest (2):

Testing for CKD: eGFR and albumin:creatinine ratio

• clinicians should use urine albumin:creatinine ratio (ACR) in preference to protein:creatinine ration (PCR) in order to detect proteinuria
  • ACR has greater sensitivity than protein:creatinine ratio (PCR) for low levels of proteinuria. For quantification and monitoring of proteinuria, PCR can be used as an alternative. ACR is the recommended method for people with diabetes
• for the initial detection of proteinuria, if the ACR is between 3 mg/mmol and 70 mg/mmol, this should be confirmed by a subsequent early morning sample. If the initial ACR is 70 mg/mmol or more, a repeat sample need not be tested
• regard a confirmed ACR of 3 mg/mmol or more as clinically important proteinuria Quantify urinary albumin or urinary protein loss as in recommendation
  • all people with diabetes, and people without diabetes with a GFR less than 60 ml/min/1.73 m^2, should have their urinary albumin/protein excretion quantified. The first abnormal result should be confirmed on an early morning sample (if not previously obtained)
  • quantify by laboratory testing the urinary albumin/protein excretion of people with an eGFR 60 ml/min/1.73 m^2 or more if there is a strong suspicion of CKD
    
    

Frequency of monitoring - Frequency of monitoring of GFR (number of times per year, by GFR and ACR category) for people with, or at risk of, CKD

• use table below to guide the frequency of GFR monitoring (per year) for people with, or at risk of, CKD, but tailor it to the person according to:
  • the underlying cause of CKD
  • past patterns of eGFR and ACR (but be aware that CKD progression is often nonlinear)
  • comorbidities, especially heart failure
  • changes to their treatment (such as renin-angiotensin-aldosterone system [RAAS] antagonists, NSAIDs and diuretics)
  • intercurrent illness whether they have chosen conservative management of CKD

Using the Table - some examples:

• CKD G3a A1 - CKD stage 3 A with an ACR less than 3 mg/mmol has a suggested requirement of x1 GFR measurement per year i.e. yearly monitoring
  
  
• CKD G3a A3 - CKD stage 3A with an ACR > 30mg/mmol has a suggested requirement of x2 GFR measurements per year i.e. 6 monthly monitoring
  
  
• CKD G5 A2- CKD stage 5 with an ACR between 3 and 30 mg/mmol has suggested requirement of >=4 GFR measurements per year

* Relative to young adult level

** Including nephrotic syndrome (ACR usually >220 mg/mmol)

Abbreviations: ACR, albumin:creatinine ratio; CKD, chronic kidney disease

Monitor people for the development or progression of CKD for at least 2-3 years after acute kidney injury, even if serum creatinine has returned to baseline

• where a highly accurate measure of GFR is required - for example, during monitoring of chemotherapy and in the evaluation of renal function in potential living donors - consider a gold standard measure (inulin, 51Cr-EDTA, 125I-iothalamate or iohexol)
• Defining progression
  • define accelerated progression of CKD as:
    • a sustained decrease in GFR of 25% or more and a change in GFR category within 12 months
    • or a sustained decrease in GFR of 15 ml/min/1.73 m2 per year
      
      
  • take the following steps to identify the rate of progression of CKD:
    • obtain a minimum of 3 GFR estimations over a period of not less than 90 days
    • in people with a new finding of reduced GFR, repeat the GFR within 2 weeks to exclude causes of acute deterioration of GFR- for example, acute kidney injury or starting renin-angiotensin system antagonist therapy
      
      
  • be aware that people with CKD are at increased risk of progression to endstage kidney disease if they have either of the following:
    • a sustained decrease in GFR of 25% or more over 12 months or
    • a sustained decrease in GFR of 15 ml/min/1.73 m^2 or more over 12 months
      
      
• NICE previously defined progressive CKD as a decline in eGFR of > 5 mL/min/1.73 m2 in one year (or 10 mL/min/1.73 m^2 in five years) (3)
  

Reference:

• (1) The Renal Association (May 2006).UK CKD Guidelines
• (2) NICE (July 2014). Chronic Kidney Disease - Early identification and management of chronic kidney disease in adults in primary and secondary care
• (3) NICE (September 2008). Chronic Kidney Disease - Early identification and management of chronic kidney disease in adults in primary and secondary care