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Chapter 6: Clinical 231

be performed in cases of deterioration of renal function
in patients with known kidney disease, to help guide
treatment, for example in systemic lupus erythemato-
Glomerular Filtration Rate (GFR) particularly to look for rejection.
sus, and relatively frequently in renal transplant patients

The biopsy can be performed percutaneously, or
at open surgery (unusual unless the other method is
not possible, or contraindicated, e.g. single kidney).
Ultrasound guidance is used, and usually two cores are
obtained using a spring-loaded biopsy needle. These are
examined under light microscopy, electron microscopy
andimmunofluoresenceorimmunoperoxidasestaining.
Serum creatinine
Complications include haematuria, bleeding under
the renal capsule and bleeding out into the retroperi-
Figure 6.2 Relationship of GFR to creatinine.
toneal space, arteriovenous aneurysm formation (if very
large may need treatment) and discomfort. In up to 3%
renal failure (creatinine clearance becomes inaccurate),
of individuals, blood transfusion is required for bleed-
for kidney donors and patients receiving chemotherapy.
ing, and in 0.1–0.4% surgery or interventional radiology
(artery embolisation using coils) is needed to stop the
Anion gap bleeding. Nephrectomy or death occur rarely.
Contraindications to percutaneous renal biopsy:
Anion gap calculation is useful in metabolic acidosis, to
Clotting abnormality or low platelets (unless cor-
differentiate causes. It is a measure of the unestimated
rected).
anions (phosphate, ketones, lactate) and cations. The
Small kidneys (<9 cm), as this indicates chronic irre-
formula used to calculate the anion gap varies from
versible kidney damage.
source to source, and the normal range depends on the
Uncontrolled hypertension.
methods by which the laboratory measures each elec-
Multiple bilateral cysts or tumour.
trolyte. For example:
Active urinary tract infection.

+
Anion gap = K + Na − Cl − HCO −
+
−
3 If there is hydronephrosis, then obstruction should
Normal range = 8 − 16mmol/L be corrected, and renal biopsy re-considered and
performed if there is still an indication.
In metabolic acidosis, an increased anion gap occurs due
Relative contraindications include obesity (technically
to raised acid levels:
difficult), single kidney (except of a transplanted kidney)
Lactic acidosis (exercise, shock, hypoxia, liver failure).

and pregnancy, as this carries special risks, but biopsy
Acid ingestion (aspirin, ethylene glycol).

may be necessary if urgent diagnosis and treatment are
Ketoacidosis.

needed.
Uraemia.

In metabolic acidosis, a normal anion gap indicates that
there is failure to excrete acid or loss of base: Dialysis
Failure to excrete acid occurs in renal tubular disease

When the kidneys fail to a degree that causes symptoms
and Addison’s disease.
and complications of renal failure, renal replacement
Loss of base (bicarbonate) occurs in diarrhoea, proxi-

therapy (RRT) is needed to remove waste products and
malrenaltubularacidosis,oriatrogenically,duetocar-
fluid, and to restore electrolytes and fluid balance to as
bonic anhydrase inhibitor or ureterosigmoidostomy.
normal as possible. There are several types of RRT, in-
cluding haemodialysis, haemofiltration and peritoneal
Renal biopsy
dialysis. Despite advances in technology, these are still
Renal biopsy is indicated when glomerular disease is sus- unable to completely mimic renal function, and none
pected,andinunexplainedacuterenalfailure.Itmayalso are able to replace the endocrine functions of the kidney.