Reflex testing to define action limits for community-based requests

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.

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.

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.

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.