4 Renal, Metabolic, and Organ Function Tests

Interpret results in context

Laboratory results are clues, not diagnoses. Interpret them alongside symptoms, vital signs, baseline results, medications, fluid balance, and the laboratory’s own reference ranges. A rapid change or concerning clinical picture may matter more than a single mildly abnormal value.

Compare results with prior values and the patient’s condition. Follow facility policy for critical results and escalation.

Renal function and electrolytes

Filtration and urine findings

Both BUN and creatinine may rise when kidney filtration is impaired. BUN can also rise with dehydration, high protein intake, burns, or some medicines; a low BUN may occur with malnutrition or liver disease. BUN alone does not establish kidney injury.

Compare BUN and creatinine with prior values, intake and output, hydration status, and medication history. A rising creatinine or an unexpected change warrants reassessment and timely reporting, especially when urine output is reduced or the patient is ill.

The eGFR estimates how well the kidneys filter and generally falls as kidney function worsens. An eGFR below $60\ \text{mL}/\text{min}/1.73\ \text{m}^2$ can indicate chronic kidney disease when persistent for at least $3$ months, but one result does not establish chronic disease. Use the trend and clinical context; eGFR is less reliable when creatinine is changing quickly, as in possible acute kidney injury.

A urine albumin-to-creatinine ratio (UACR) above $30\ \text{mg}/\text{g}$ is abnormal and may indicate kidney damage even when eGFR is $60$ or higher. Report and follow up abnormal results. A clinician may repeat testing to confirm because temporary factors can affect a single result.

Electrolytes and urgent findings

Kidney dysfunction can disturb potassium and acid–base balance. Potassium that is too high or too low can affect heart rhythm and muscle function. Promptly escalate a critical or unexpected potassium result according to policy, and reassess for weakness, palpitations, or rhythm changes. If a result does not fit the patient’s condition, follow policy for verification; do not delay urgent escalation when the patient is unstable.

Markedly reduced or absent urine, rapidly worsening renal results, new swelling or breathlessness, confusion, or a critical electrolyte result requires prompt assessment and communication. Compare urine output with the patient’s baseline and care plan, and do not wait for a laboratory value if the patient is deteriorating.

Glucose tests and urgent changes

Diagnostic thresholds and interpretation

For fasting plasma glucose (FPG), $100$–$125\ \text{mg}/\text{dL}$ is in the prediabetes range, and $126\ \text{mg}/\text{dL}$ or higher is in the diabetes range. For A1C, $5.7\%$–$6.4\%$ is in the prediabetes range, and $6.5\%$ or higher is in the diabetes range. In the absence of clear symptoms, diagnostic results generally need confirmation. These are diagnostic thresholds, not individualized treatment targets.

A random glucose of $200\ \text{mg}/\text{dL}$ or higher with classic hyperglycemia symptoms may support diagnosis, but an isolated reading must be interpreted in context. A1C reflects longer-term average glucose, not an acute glucose level.

Low glucose and escalation

A glucose below $70\ \text{mg}/\text{dL}$ is an alert threshold; below $54\ \text{mg}/\text{dL}$ is more serious. Altered mental or physical status requiring assistance is severe hypoglycemia regardless of the measured value. Follow the patient’s orders and facility hypoglycemia protocol, then recheck as directed.

If the patient is unconscious or cannot swallow safely, do not give oral food or drink; activate the emergency response and follow protocol. Escalate promptly for symptomatic low glucose, confusion, or seizure. Also escalate severe hyperglycemia accompanied by vomiting, dehydration, deep or labored breathing, or altered mental status. Assess the patient first.

Liver markers and patterns

ALT and AST elevations out of proportion to alkaline phosphatase (ALP) suggest a predominantly hepatocellular pattern. AST can also come from tissues outside the liver, including muscle.

A rise in ALP out of proportion to ALT and AST suggests a cholestatic pattern, associated with reduced bile flow or obstruction. Other tests and clinical assessment help identify the source.

Bilirubin elevation may occur with hepatocellular disease or cholestasis. Jaundice, dark urine, or pale stools with rising bilirubin should be reported and assessed.

Albumin and PT/INR can help assess the liver’s protein-making function, but other conditions affect them, so they are not interpreted alone. Low albumin is not specific to liver disease. Prolonged PT/INR can indicate impaired clotting and needs prompt clinical review, particularly if bleeding is present.

Liver enzyme tests indicate possible injury or a pattern; by themselves, they do not identify a specific cause or fully measure liver function. Escalate new jaundice with worsening condition, bleeding, unusual bruising, confusion, or reduced alertness for prompt assessment.

Pancreatic markers

Lipase is generally preferred over amylase when acute pancreatitis is suspected. A substantial elevation—often around $3$ or more times the laboratory’s upper limit of normal—together with compatible upper abdominal pain supports concern for pancreatitis, but the result is not diagnostic in isolation. Lipase can also rise with kidney disease and other conditions.

Reassess and escalate severe, persistent upper abdominal pain, especially pain radiating to the back, repeated vomiting, fever, hypotension, or worsening condition. Do not dismiss concerning symptoms because a pancreatic enzyme is normal or only mildly elevated.

A practical interpretation sequence

Use a consistent sequence to connect the patient’s condition with the laboratory result:

1. Check the patient: assess symptoms, vital signs, mental status, urine output, and immediate safety concerns.

2. Check the result: review units, the laboratory’s reference range, any critical flag, possible specimen or reporting concerns, and change from baseline.

3. Look for a pattern: consider renal filtration together with urine albumin; glucose with symptoms; ALT and AST relative to ALP and bilirubin; and lipase alongside abdominal symptoms.

4. Act and communicate: follow orders and facility policy, document reassessment, and promptly notify the appropriate clinician about critical, rapidly changing, or clinically concerning findings.

Trends and clinical status guide interpretation: renal assessment uses creatinine and eGFR together with urine albumin and the patient’s condition; glucose thresholds classify results, while symptoms and immediate measurements guide urgent action; liver markers are read as patterns; and lipase is interpreted alongside symptoms rather than alone.