Creatinine

Creatinine = Non-protein end product of creatinine metabolism. Formed from skeletal muscle and excreted in constant amounts. Completely filtered by kidney (marker of GFR). Production proportional to muscle mass

• Relatively unaffected by diet, exercise or urine volume
• More sensitive test of renal damage.  Elevation of levels almost exclusively secondary to renal impairment
• Clearance is an excellent indicator of kidney efficiency in clearing creatinine
  • Clearance levels become abnormal when >50% of nephron units have become damaged

Causes of increased serum creatinine

1. Renal impairment (>50% nephrons affected) – any cause of renal failure, basically
   • Pre-renal
     • Decreased perfusion to the kidney
     • Dehydration, hypovolaemia, shock
   • Renal
     • Intrinsic renal lesion
     • Nephrotoxic drugs
   • Post renal obstruction
2. Nephrotoxic drugs
   • NSAID, aspirin, indomethacin
   • Ampicillin, rifampicin, cephalosporin, aminoglycosides
   • Frusemide, Thiazides, acetazolamide, mannitol
   • Lithium, iron, lead, copper, gold
3. Metabolic
   • Acromegaly
   • Hyperthyroidism
   • Very large muscle mass (athletes) (without renal compromise)
   • NOT affected by dietary protein intake
4. Fictitious
   • Interfere with colorimetric analysis (Glucose, fructose, ascorbic acid)

Causes of a Decreased Creatinine

• Pregnancy
• Conditions characterised by muscle wasting

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, ABDO: Gas on abdominal X-ray, Kidney mass, BRAIN: Intracranial calcification, Intracranial structures with contrast, Ventriculomegaly, OTHER: Pseudofracture on X-Ray,
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

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