- Chris Nickson
OVERVIEW
Principle
- urea and creatinine both freely filtered at the glomerulus
- creatinine is not reabsorbed
- urea reabsorbed by tubules via regulation
- can be used as an indicator of the likely cause of renal failure
Normal Urea – 2.5-10.7mmol/L
Normal Creatinine – 62-106umol/L -> 0.062 – 0.106mmol/L (divide micromoles by 1000)
The relationship of urea and creatine is dependent on serum laboratory units used to determine the cause of acute kidney injury.
- In the US the urea is expressed as BUN (Blood Urea Nitrogen) in mg/dL.
- Elsewhere Urea (U) is expressed as mmol/L
- Similarly, Creatinine (Cr) is expressed as mg/dL in the US and µmol/L elsewhere
Conversion: SI to traditional units
- Plasma urea: 10 mmol/l = 27.8 mg/100 ml
- Plasma creatinine: 100 µmol/ – 1.13 mg/100 ml.
Therefore two ratio’s exist to compare serum Urea and Creatinine levels
- BUN : Cr ratio with US units of mg/dL : mg/dL – this is most commonly used in online calculators and converts the SI units to US units e.g. MDcalc
- Urea : Cr ratio with SI Units of mmol/L:mmol/L (providing Urea is >10mmol/L) – [note to calculate the Urea : Cr ratio it is required to convert the Creatinine from µmol/L to mmol/L] [hat tip Dr Julian Pecora]
- Cr : Urea ratio with SI Units of µmol/L:mmol/L (providing Urea is >10mmol/L)
CAUSES
Urea:Creatinine Ratio (in the setting of renal failure / elevated creatinine)
- 40-100:1 – normal or post renal cause of AKI
- >100:1 – pre-renal cause (urea absorption increased compared to creatinine)
- <40:1 – intrinsic renal damage (urea unable to be absorbed -> become like creatinine -> ratio gets closer to 1)
Other causes:
INCREASED UREA:CREATININE RATIO – (Drivers Can use GPS)
- dehydration/prerenal failure
- corticosteroids
- GI haemorrhage
- protein-rich diet
- severe catabolic state
DECREASED UREA:CREATININE RATIO (I am a SIMPLE SR)
- severe liver dysfunction
- intrinsic renal damage
- malnutrition
- pregnancy
- low protein diet
- SIADH
- rhabdomyolysis
References
- Morgan DB, Carver ME, Payne RB. Plasma creatinine and urea: creatinine ratio in patients with raised plasma urea. Br Med J. 1977 Oct 8;2(6092):929-32
- Witting MD, Magder L, Heins AE, Mattu A, Granja CA, Baumgarten M. ED predictors of upper gastrointestinal tract bleeding in patients without hematemesis. Am J Emerg Med. 2006 May;24(3):280-5. PMID 16635697
- Urashima M, Toyoda S, Nakano T, Matsuda S, Kobayashi N, Kitajima H, Tokushige A, Horita H, Akatsuka J, Maekawa K. BUN/Cr ratio as an index of gastrointestinal bleeding mass in children. J Pediatr Gastroenterol Nutr1992 Jul;15(1):89-92. PMID 1403455.
- Feinfeld DA, Bargouthi H, Niaz Q, Carvounis CP. Massive and disproportionate elevation of blood urea nitrogen in acute azotemia. Int Urol Nephrol. 2002;34(1):143-5. PMID 12549657
CCC Differential Diagnosis Series | |
NEURO | Anosmia, Ataxia, Blepharospasm, Bulbar and Pseudobulbar palsy, Central Pontine Myelinosis, Cerebellar Disease, Chorea, Cranial nerve lesions, Dementia, Dystonia, Exophthalmos, Eye trauma, Facial twitches, Fixed dilated pupil, Horner syndrome, Loss of vision, Meningism, Movement disorders, Optic disc abnormality, Parkinsonism, Peripheral neuropathy, Radiculopathy, Red eye, Retinal Haemorrhage, Seizures, Sudden severe headache, Tremor, Tunnel vision |
RESP | Bronchial breath sounds, Bronchiectasis, High airway pressures, Massive haemoptysis, Sore throat, Tracheal displacement |
CVS | Atrial Fibrillation, Bradycardia, Cardiac Failure, Chest Pain, Murmurs, Post-resuscitation syndrome, Pulseless Electrical Activity (PEA), Pulsus Paradoxus, Shock, Supraventricular tachycardia (SVT), Tachycardia, VT and VF, SVC Obstruction |
GIT | Abdominal distension, Abdominal mass, Abdominal pain, Asterixis, Dysphagia, Hepatomegaly, Hepatosplenomegaly, Large bowel obstruction, Liver palpation abnormalities, Lower GI haemorrhage, Malabsorption, Medical causes of abdominal pain, Rectal mass, Small bowel obstruction, Upper GI Haemorrhage |
GUT | Genital ulcers, Groin lump, Scrotal mass, Urine colour, Urine Odour, Urine transparency, |
MSK | Arthritis, Shoulder pain, Wasting of the small muscles of the hand |
DERM | Palmar erythema, Serious skin signs in sick patients, Thickened Tethered Skin, Leg ulcers, Skin Tumour, Acanthosis Nigricans |
ENDO | Diabetes Insipidus, Diffuse Goitre, Gynaecomastia, Hirsutism, Hypoglycaemia, SIADH, Weight Loss |
HAEM | Splenomegaly |
PAEDS | Floppy infant |
MISC | Anaphylaxis, Autoimmune associated diseases, Clubbing, Parotid Swelling, Splinter haemorrhages, Toxic agents and abnormal vitals, Toxicological causes of cardiac arrest |
IMAGING | CHEST:Atelectasis, Hilar adenopathy, Hilar enlargement on CXR, Honeycomb lung, Increased interstitial markings, Mediastinal widening on mobile CXR, Pulmonary fibrosis, Pseudoinfiltrates on CXR, Pulmonary opacities on CXR, |
LABS | LOW:Anaemia, Hypocalcaemia, hypochloraemia, Hypomagnesaemia, HIGH:Bilirubin and Jaundice, Hyperammonaemia,Hypercalcaemia, Hyperchloraemia, Hyperkalaemia, Hypermagnesaemia, ACID BASE:Acid base disorders, Resp. acidosis, Resp. alkalosis, Creatinine, CRP, Dipstick Urinalysis, Laboratory Urinalysis, Liver function tests (LFTs), Pleural fluid analysis, Urea, Urea Creatinine Ratio, Uric acid, Urinalysis, Urine Electrolytes |
Critical Care
Compendium
…more CCC
Chris Nickson
Chris is an Intensivist and ECMO specialist at theAlfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University.He is a co-founder of theAustralia and New Zealand Clinician Educator Network(ANZCEN) and is the Lead for theANZCEN Clinician Educator Incubatorprogramme. He is on the Board of Directors for theIntensive Care Foundationand is a First Part Examiner for theCollege of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s educationwebsite,INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of theFOAMmovement (Free Open-Access Medical education) and is co-creator oflitfl.com,theRAGE podcast, theResuscitologycourse, and theSMACCconference.
His one great achievement is being the father of three amazing children.
OnTwitter, he is@precordialthump.
| INTENSIVE | RAGE | Resuscitology | SMACC
Leave a Reply
This site uses Akismet to reduce spam. Learn how your comment data is processed.
