A Lab Value Is a Call, Not a Fact

The four zones

• Normal. Document it and move on. A normal value is data, not an event.
• Abnormal. Monitor and look for the trend. One abnormal value is a question, not an answer.
• Critical. Stop and call. The value has crossed the line the laboratory set for callback.
• Incompatible with delay. Act while you call. Airway, rhythm, and level of consciousness do not wait for a returned page.

Direction beats digit

A potassium of 5.4 mEq/L falling from 6.8 mEq/L is a different patient from a 5.4 mEq/L climbing from 4.1 mEq/L. The first is a treatment working. The second is a treatment failing. Same digit, opposite decisions. Reference range 3.5 to 5.0 mEq/L.

Tempo

How fast the value moved is the second question. A sodium of 128 mEq/L that developed over an hour seizes. The same 128 mEq/L that developed over three weeks walks and talks, because the brain had time to adapt. Reference range 135 to 145 mEq/L. Ask which way, then how fast, then how far from the line.

Reading one result

Three questions, always in this order. Where does it sit against the range. Which way is it moving compared with the last draw. How long did the move take. Only then do you choose an action, and the action for most abnormal values is another assessment, not a treatment.

Margin noteask which way, then how fast.

Watch outa single value that sits inside the reference range can still be an emergency if it arrived there fast, or if it is heading out of the range at speed. A normal number is not a normal patient.

Memory hookZONE, then DIRECTION, then TEMPO. A value with no comparison is half a result.

☐ I can name the four zones and the action each one requires.

→ BOOK 01 · P31 for the master reference cards this page assumes.

Takeawayread the value, then the direction, then the tempo, and only then choose the action.

Reference ranges vary between institutions and reference laboratories. Follow local protocol.