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The Chemical Pathology department will make every effort to inform clinicians of critical blood results which require urgent clinical intervention (These critical blood result phoning limits have been set in accordance with Royal College of Pathology guidelines and following consultation with CCG clinical lead and secondary care clinicians).

The stated limits serve as a guide only (below;) they are not exhaustive and laboratory staff should check with the Chemical Pathology Consultant, if unsure as to the suitability of communicating given data-sets by phone.

Generally, if the observed data is consistent with past (deranged) findings that have already been communicated as a matter of urgency previously, then the most recent results will not typically be phoned but will instead be released in the normal manner unless specifically requested otherwise.

Critical result limits



GP/ Out-patients


Sodium (mmol/L) <125  >155  <125  >150  
Potassium (mmol/L) <2.8  >6.0 As for in-patients* >6.5 renal failure
>7.0 neonates
Urea (mmol/L) >30 >30 Initial specimen
Creatinine (µmol/L) >300 >200 Initial specimen
Glucose (mmol/L) <2.8  >25.0 >20.0 or >25.0 if known DM  
Triglycerides (mmol/L) >20.0 >20.0  
Calcium (mmol/L) <1.8  >3.0 As for in-patients Corrected for albumin
Magnesium (mmol/L) <0.4  >2.0
>3.5 (Pre-eclampsia)
As for in-patients  
Phosphate (mmol/L) <0.3 As for in-patients  
Iron (µmol/L) >30 Children
>50 Adults
As for in-patients  
AST (U/L)   >600 (15x ULN)  
ALT (U/L)   >525 (15 x ULN)  
CK (U/L)   >2000  
Amylase (U/L) ≥250 As for in-patients  
Bile acids (mmol/L) >20 As for in-patients  
Phenytoin (µmol/L) >80 if [Alb] >40g/L
>60 if [Alb] <35g/L
As for in-patients In renal failure phone all results
Carbamazepine (µmol/L) >70 As for in-patients  
Digoxin (nmol/L) >3.0 As for in-patients Phone if >2.0 if [K+] or [Mg2+] low and/or in renal impairment
Theophylline (µmol/L) >120 Adults
>60 Children
As for in-patients  
Lithium (mmol/L) >1.00 As for in-patients  
CSF protein (g/L)
CSF glucose (mmol/L)
Phone all results    
CSF Xanthachromia Phone all results  N/A Refer to LI-BIO-I093 for sample collection details
Paracetamol (mg/L) >25.0 As for in-patients Note time of ingestion
Salicylate (mg/L) >50.0 As for in-patients Note time of ingestion
TSH (mIU/L) >75 >50  
FT4 (pmol/L) <5.0  >40.0 As for in-patients  
FT3 (pmol/L) >8.0 As for in-patients  
Cortisol (nmol/L) <50.0 As for in-patients Telephoning not required if post-dexamethasone suppression test

 *(<2.8 >6.5 if OOH - all out of range results (2.5-6.5) to be phoned to GP next working day regardless)

Last updated: 15 December 2015