Investigations for Renal Disease

Introduction

Given that renal diseases have a wide range of clinical presentations and differential diagnoses, it is important to remember the tools available at your disposal to help in reaching a diagnosis. The following investigations have been arranged from the simplest and least invasive tests, which should be routinely done when evaluating renal diseases, to more invasive and complex assessments.

Urine dipstick

Urine dipstick tests can check for the presence of various constituents suggesting the presence of pathology.

1. Blood:
   1. On start of voiding: Urethral source
   2. Throughout urination: source is from bladder or above.
   3. End of voiding: source is from prostate or bladder base
2. Protein: suggests intrinsic renal disease. However, note that this does not detect immunoglobulins or light chains (e.g. as found in multiple myeloma)
3. Glucose: suggests diabetes mellitus
4. Nitrite: positive result suggests urinary tract infection; produced by bacteria that are able to reduce nitrates to nitrites
5. pH level: low pH suggests renal tubular acidosis
6. Bilirubin: suggests obstructive jaundice
7. Ketones: Starvation

Urine microscopy and culture

Urine microscopy and culture can be performed to check for the presence of infection and identify responsible organisms.

Blood tests

Basic tests

The main blood tests to arrange for most renal diseases are:

1. Urea and electrolytes: an increase in urea and creatinine suggests a reduction in glomerular filtration rate and renal damage. However, this is not sensitive as >50% of kidney needs to be destroyed to produce an effect on these tests. Additional factors to consider when interpreting these tests include:
   1. Creatinine: bodybuilders have high creatinine levels, so can have a misleadingly low estimated GFR if calculated using creatinine
   2. Urea: levels are reduced in liver disease and malnutrition
2. Full blood count: detects for the presence of normochromic normocytic anaemia as a result of reduced erythropoietin production. Alternatively, renal tumours and cysts can increase EPO production and produce polycythaemia

Further blood tests to consider

Further investigations may include:

1. Calcium levels: measure as renal disease can reduce calcitriol levels, reducing calcium levels. This may be accompanied by secondary hyperparathyroidism acting as a feedback mechanism.
2. Immunology tests: check for autoimmune conditions, especially when investigating glomerulonephritis. Tests can include:
   • Anti-glomerular basement membrane (anti-GBM) antibody: Goodpasture’s syndrome
   • Anti-neutrophil cytoplasmic antibody (ANCA): check for ANCA-associated vasculitides e.g. Granulomatosis with polyangiitis
   • Antistreptolysin O titres (ASOT): high titres suggest post-streptococcal glomerulonephritis
   • Anti-double stranded DNA (anti-dsDNA): suggest systemic lupus erythematosus
   • Immunoglobulin levels: high IgA levels in IgA nephropathy
   • C3, C4 levels: low complement levels may be found in systemic lupus erythematosus and IgA nephropathy

Imaging

1. Renal ultrasound can be used to check for:
   • Urinary tract obstruction
   • Renal tumours / cysts
   • Renal stones
2. CT/MRI scans can be used to check for:
   • Renal stones
   • Mass lesion
3. Renal arteriography: checks for renal artery stenosis

Renal biopsy

Performing a renal biopsy is an invasive procedure that can be considered to assist in making a definitive diagnosis in the following conditions:

1. Glomerulonephritis
2. Unexplained acute kidney injury (AKI) or chronic kidney disease (CKD)
3. Renal cancer