What Is Acute Renal Failure

Published Date: 02 Nov 2017

What is acute renal failure?

Acute renal failure or acute renal injury occurs when the kidney loses its function in a rapid manner instead of gradually, which is seen in chronic renal failure.

There are 3 different types of acute renal failure:

Prerenal failure: problem occurs before the blood enters the kidney.

Renal failure: problem occurs in the kidney.

Intrinsic renal failure: problem occurs after the filtration of blood and when the waste products are being exposed of as urine.

Lab diagnosis is usually the first to recognize renal impairment. These results are important in the treatment of renal failure. The two main areas of diagnosis of acute renal failure is done in Haematology and Chemical Pathology laboratories.

Tests used to diagnosis acute renal failure in the lab:

Urine Tests:

Dipstick Test:

A small amount of urine is collected from a patient into a universal collection bottle, which is done in the doctors’ surgery. The doctor uses a reagent strip(dipstick) and puts it in the urine to check if there is any presence of blood, infection or proteins in the urine.

24 hour urine

Urine is collected from a patient over a period of 24 hours, this is done by collecting urine every time in the period of 24 hours. It is collected in a bottle and store at room temperature or refrigerated, which is then sent to the chemistry lab for testing. This test will determine how much urine the kidney produced within 24 hours (if there is insufficient excretion of fluid from the body, oedema occurs), how much protein is being excreted (this should not be high) and how much creatinine and urea is excreted (this should not be low, if it is then it means that the kidney is not excreting waste products properly, causing ureamia).

Blood tests:

Serum creatinine

Creatinine is a waste product of the body and is excreted by the kidneys on filtration. Ultimately increase creatinine levels should be found in the urine instead of the blood.

Normal range: 0.8-1.4mg/dl

If there is an increase of ≥ 26µmol/l within 48hrs, its possible to be ARF.

Glomerular filtration rate

This test is done to determine how well the kidneys are functioning.

It is calculated by:

Ccreat = cretainine clearance rate in ml/min

Ucreat = urinary creatinine in mg/dl

⊽ = urine flow in ml/min

P = serum creatinine in mg/dl

Normal reference ranges:

Males: 97-137ml/min

Females: 75-115ml/min

Microalbumin

Albumin is found in urine when vessels in the kidney are damaged and allows the albumin to leak out.

Normal range: <30mg over 24hrs

Abnormal: 30-300mg

BUN- blood urea nitrogen

BUN is used to determine how much of waste products are present in the blood stream. If urea levels were to increase in the blood stream, this would mean that the kidney is not filtering the blood problem.

Normal reference range: 7-18mg/dl

Abnormal: if above range

Creatinine clearance

This test determines how much creatinine is being excreted by the kidney. This test works in correlation with serum creatinine. A blood test will be taken from the patient to determine how much of creatinine is in the blood and a urine test will be taken hereafter to determine how much creatinine was excreted. Another blood test will be done after urination to determine how much of creatinine is left in the blood.

Normal reference ranges:

Males: 97-137ml/min

Female: 88-128ml/min

Abnormal: less than normal range

Urea

Urea is produced when protein is degraded, which makes it a waste product of the body. There would be an increase in the excreation of urea which indicates kidney damage.

Calcium and Phosphorous

The kidney produces calcitriol (used to maintain blood calcium levels), if the kidney is damaged, this would not be produced so the levels would not be made.

Haemoglobin

This test is important because the kidney is responsible for producing epo, which stimulates the bone marrow to produce red cells. Red cells contain haemoglobin so when there is a problem with the kidney, not enough epo will be produced, there will be a decrease in red cells hence there will be a decrease in haemoglobin, causing anaemia

Normal reference ranges:

Males: more than 13g/dl

Female: more than 12g/dl

Abnormal: less than normal range

Haematocrit

This test determines how much red cells are being made in relation to the rest of the blood cells. A low haematocrit indicates that not enough red cells are being made.

Normal reference ranges:

Males: 41-53%

Females: 36-46%

Platelet count

Platelet count decreases because there is defective production of platelets. This results in pancytopaenia.

Effects of Kidney Failure:

Ureamia- Due to the accumulation of toxins in the blood.

Fluid retention- Due to a problem with the kidney, there would not be sufficient excretion of fluid from the body causing oedema.

Hyperkalaemia- Increase levels of potassium in the blood, can cause cardiac arrhythmias.

Anaemia- Because the kidney produces Epo to prompt the bone marrow to produce red cells, the red cell count would not be normal (below range). The lack of red blood cells causes anaemia. Anaemia will be normocytic normochromic.

Bone diseases- the kidney would not be producing enough calcitrol, calcium and phosphorous would not be absorbed.

schistocytes in hus.JPG

Schistocytes

http://www.pitt.edu/~moizst19/leoa.html

normo normo.JPG

normocytic normochromic anaemia http://www.bpac.org.nz/resources/campaign/cbc/bpac_cbc_best_tests.pdf

Conclusion:

Normocytic normochromic aneamia is usually seen in acute renal failure. Anaemia rises because of the lack of erythropoiesis and production ureamia, which reduces the life span of red cells in circulation. Acute renal failure can be linked with MAHA (Microangiopathic haemolytic anaemia) and HUS (haemolytic uremic syndrome). It is important for patients to seek medical attention when signs and symptoms of acute renal failure arise. Doctors use dialysis to prevent the buildup of toxins in the body, also antibiotics are used to clear out any infections that could have occurred. Special diets are recommended so that the kidney will not be under more stress.