6 Integrated Laboratory Interpretation Practice

Interpret results in clinical context

Interpret results alongside the patient’s condition, not in isolation. Check the reporting laboratory’s reference interval, compare the result with prior values, and consider collection problems or medications. Also assess vital signs, symptoms, urine output, and mental status.

Reference intervals vary by laboratory, age, and other patient factors. A rapidly changing result or a symptomatic patient may be more concerning than a single mildly abnormal value. The approximate adult values below are teaching approximations, not universal decision thresholds; use the reporting laboratory’s range.

• Sodium: approximately $135\text{–}145\,\text{mmol/L}$; relevant to fluid balance and neurologic function.

• Potassium: approximately $3.5\text{–}5.0\,\text{mmol/L}$; relevant to cardiac conduction and muscle function.

• Fasting glucose: approximately $70\text{–}99\,\text{mg/dL}$; low levels can impair brain function, while high levels may reflect diabetes or acute illness.

• Creatinine: approximately $0.6\text{–}1.3\,\text{mg/dL}$; interpret with baseline, estimated glomerular filtration rate, and urine output.

• White blood cells: approximately $4\text{–}11 \times 10^9/\text{L}$; levels may rise with infection or other stress, and a normal count does not exclude serious illness.

• Platelets: approximately $150\text{–}400 \times 10^9/\text{L}$; low counts can increase bleeding risk.

• Hemoglobin: approximately $12\text{–}16\,\text{g/dL}$ in adult women and $13.5\text{–}17.5\,\text{g/dL}$ in adult men; it relates to oxygen-carrying capacity, and trends and symptoms matter.

• Lactate: often less than $2\,\text{mmol/L}$; it may rise with impaired perfusion but is not diagnostic by itself.

Respond to rising potassium with ECG changes

A patient with chronic kidney disease reports new weakness. Potassium rises from $5.2$ to $6.4\,\text{mmol/L}$, creatinine is above baseline, and the ECG shows new peaked T waves. Hyperkalemia with ECG changes can signal dangerous cardiac effects.

Notify the responsible clinician immediately, initiate continuous cardiac monitoring, and obtain urgent evaluation under facility protocol. Prepare to carry out ordered emergency treatment. A hemolyzed specimen can falsely elevate potassium, so repeat testing may be appropriate, but do not let verification delay action when ECG changes or instability are present.

Do not wait for the next scheduled blood draw or for symptoms to worsen, and do not encourage a high-potassium snack in this situation.

Act on low glucose and altered mental status

A patient receiving insulin is diaphoretic and confused, with a point-of-care glucose of $42\,\text{mg/dL}$, and cannot safely swallow. Altered mental status with low glucose is an urgent safety problem.

Protect the patient from injury, call for help, and administer glucagon or intravenous dextrose as authorized by protocol or order. Then recheck glucose, reassess, and continue monitoring. Do not give oral food or fluid to someone who cannot swallow safely, wait before intervening, or give the scheduled insulin dose.

The oral carbohydrate approach of $15$ grams applies to people who are awake and able to swallow safely. Use the facility’s emergency hypoglycemia protocol.

Recognize possible worsening perfusion

An older adult with suspected infection becomes more drowsy. Blood pressure is $86/50\,\text{mmHg}$, heart rate is $122/\text{min}$, and urine output has fallen. Lactate rises from $2.1$ to $4.3\,\text{mmol/L}$, and white blood cells are $18 \times 10^9/\text{L}$.

Hypotension, altered mentation, and reduced urine output are concerning together. The rising lactate adds evidence of possible impaired perfusion, but does not establish a diagnosis by itself. A white-cell count alone does not confirm sepsis, and a nonspecific lactate result should not be ignored.

Urgently escalate care, reassess airway, breathing, and circulation, and reassess vital signs. Sepsis and septic shock are emergencies. Anticipate time-sensitive orders and monitoring, carry out the treatment plan, and continue reassessing. Interpret lactate in clinical context; fluid therapy should be individualized and monitored rather than given without reassessment.

Prioritize signs of bleeding and instability

A patient reports black, tarry stools. Hemoglobin falls from $11.4$ to $8.7\,\text{g/dL}$ over several hours. The patient is pale and diaphoretic, heart rate is $126/\text{min}$, blood pressure is $90/56\,\text{mmHg}$, and urine output is decreasing.

Treat this as possible significant blood loss with hemodynamic instability. Escalate urgently, assess airway and circulation, monitor closely, and prepare for ordered resuscitation and further evaluation. Vital-sign and perfusion changes are more urgent than any single hemoglobin threshold. With acute bleeding, hemoglobin trends may not immediately reflect the full blood loss.

Stabilization and rapid evaluation take priority. Decisions about fluids or blood products depend on the clinical situation and authorized treatment plan. Do not wait for the next complete blood count, encourage the patient to walk, or reassure the patient solely because hemoglobin is not below $7\,\text{g/dL}$.

Apply a safe interpretation approach

Prioritize the patient, not the number: recognize dangerous symptoms and trends, compare results with baseline and the laboratory’s range, and promptly escalate critical findings. Recheck a questionable result when appropriate, but do not delay urgent care when the patient is unstable or assessment findings are concerning.

Follow facility policy, scope of practice, and orders when initiating treatment.

• Hypoperfusion