Reflex testing to define action limits for community-based requests.

Background: Critical values are required to be phoned 24/7. Other abnormal results fall short of the thresholds used to define critical values and may only be required to be phoned during the day. Community-based requestors prefer not to be contacted unless a result is critical and contacting them requires substantial staff resource. It is common practice to add tests to requests to expedite diagnosis or clarify the significance of a particular result using algorithms.

Methods: We devised algorithms for reflex addition of tests which allowed the differentiation of significantly abnormal results as either critical values or those that only require day phoning.

Results: Algorithms identified 158 out of 309 tests as being critical (51%) over nine months. Reflex addition of serum bicarbonate identified 4% of serum glucose (24.9-37.9 mmol/L) as critical. Use of estimated glomerular filtration rate by reflex addition of serum creatinine identified 68% of serum lithium (1.49-1.99 mmol/L) as critical. Addition of serum potassium, calcium and magnesium identified 21% of serum digoxin (>2.49 nmol/L) as critical and addition of serum potassium and calcium to all samples with serum magnesium (<0.31 mmol/L) identified hypocalcaemia in all cases. The addition of serum creatinine and potassium as markers for rhabdomyolysis-induced acute renal failure did not help in the differentiation of serum creatine kinase>4999 μ/L.

Conclusions: Use of reflex tests helped inform a phoning system based on the division of results into critical values and non-emergency abnormal values. This avoids disturbing requestors unnecessarily and conserves staff time at night.