Chronic kidney disease
Investigations
1st investigations to order
renal chemistry
Test
Includes sodium, potassium, chloride, bicarbonate, urea, creatinine, and glucose.
Serum creatinine alone is insufficient to determine CKD and may be falsely low in conditions of low muscle mass, as in older or malnourished people, or patients with liver failure.
Normal creatinine in men is 70 to 120 micromol/L (0.8 to 1.4 mg/dL), and in women 50 to 97 micromol/L (0.6 to 1.1 mg/dL). However, there is significant variation due to calibration methods between laboratories.[3]
Electrolyte abnormalities may indicate an underlying cause of CKD, such as tubular disorders.[1] Adaptations in acid excretion by the kidneys initially prevent a fall in serum bicarbonate concentration, but as GFR declines, metabolic acidosis develops.[1]
Result
elevated serum creatinine; electrolyte abnormalities
estimation of GFR
Test
A GFR estimating equation using serum creatinine is recommended for initial assessment.
Determines more accurately, by mathematical equations such as the CKD EPI equation, the GFR and the severity and stage of CKD.[55]
Laboratories should estimate GFR using an equation without a race variable.[48][49][50] National Kidney Foundation: eGFR calculator Opens in new window [ Glomerular Filtration Rate Estimation (eGFR) by Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) Equation with Creatinine, without Race (2021) ]
Formulas have not been proven to be reliable estimators in patients with a GFR >59 mL/minute/1.73 m².[1]
Result
<60 mL/minute/1.73 m²
serum cystatin C and cystatin C-based estimation of GFR
Test
Warranted in specific circumstances when GFR estimates based on serum creatinine are thought to be inaccurate, such as in people with extremes of muscle mass (e.g., bodybuilders, people with muscle-wasting disorders, older or malnourished people).[1]
Laboratories should estimate GFR using an equation without a race variable.[48][49][50] National Kidney Foundation: eGFR calculator Opens in new window [ Glomerular Filtration Rate Estimation (eGFR) by CKD-EPI Equation with Cystatin C, without Race (2012) ] [ Glomerular Filtration Rate Estimation (eGFR) by CKD-EPI Equation with Creatinine and Cystatin C, without Race (2021) ]
Result
reduced muscle mass will lead to overestimation; increased muscle mass to underestimation of the GFR
urinalysis
Test
Screening test to determine for pathological markers of kidney damage excreted in the urine.
Result
haematuria and/or proteinuria
urinary albumin
Test
Classification of CKD requires quantification of urinary albumin as based on albumin excretion rate (AER) or albumin to creatinine ratio (ACR).[1][50] Moderately increased albuminuria is a risk factor for the development of progressive CKD and coronary artery disease associated with diabetes and hypertension. Indicated in patients with diabetes and CKD if there was no evidence of proteinuria on urine dipstick.[56]
Result
moderately increased (AER 30-300 mg/day; ACR 30-300 mg/g)
Investigations to consider
kidney biopsy
Test
Helps to determine pathological diagnosis of CKD in glomerular nephrotic and nephritic syndromes, and in people with diabetes with atypical presentations such as rapidly progressive kidney failure. Also essential in determining whether pathological lesions are due to infection (e.g., hepatitis B and C, syphilis, and streptococcal pharyngitis). Provides insight into treatment options based on severity or chronicity of scarring of glomeruli and interstitium.
Result
variable depending on aetiology
plain abdominal radiograph
Test
Non-specific test that may aid in the detection of calcium-containing kidney stones, as medicine and urate stones are not apparent on plain radiography.
Result
may reveal calcium-containing kidney stones
abdominal CT
Test
Imaging test that is helpful to determine the presence or absence of kidney stones and confirms obstructive component. It is also helpful to further evaluate cystic lesions or mass lesions in the kidney. Intravenous contrast is used with caution in high-risk patients, such as those with CKD with a reduction in the estimated GFR <60 mL/minute, as it can cause acute kidney injury. Prophylaxis with intravenous normal saline may be indicated or considered in some patients.[57]
Result
may reveal kidney stones, renal masses, or cysts
abdominal MRI
Test
Imaging test that further characterises mass lesions in the kidney, such as renal cell carcinoma.
Gadolinium-based MRI examinations have been associated with nephrogenic systemic fibrosis in patients with kidney disease. However, not all gadolinium-containing contrast agents have the same risk of nephrogenic systemic fibrosis, and the benefits of gadolinium-based MRI use may exceed its risk.[58]
Result
may reveal mass lesions in the kidney
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