Which of the following laboratory values are abnormal: sodium 141 mmol/L, potassium 4.5 mmol/L, chloride 106 mmol/L, total CO₂ 17 mmol/L, BUN 7 mg/dL, creatinine 0.5 mg/dL, GFR >78 mL/min/1.73 m², glucose 109 mg/dL, calcium 8.9 mg/dL, AST 29 U/L, ALT 32 U/L, alkaline phosphatase 80 U/L, bilirubin 0.2 mg/dL, albumin 3.9 g/dL, total protein 5.8 g/dL?

Abnormal Laboratory Values

The abnormal values in this panel are: Total CO₂ 17 mmol/L (low bicarbonate indicating metabolic acidosis), BUN 7 mg/dL (low), and Total Protein 5.8 g/dL (low).

Detailed Analysis of Abnormalities

Total CO₂ (Bicarbonate) - 17 mmol/L

This represents a non-anion gap metabolic acidosis (normal range typically 22-29 mmol/L). With the provided electrolytes, the anion gap calculates to approximately 18.5 mmol/L (Sodium 141 - Chloride 106 - CO₂ 17), which is within normal limits (8-12 mmol/L), confirming this is a non-anion gap acidosis 1.

Clinical significance:

• This degree of acidosis warrants investigation for causes including renal tubular acidosis, diarrhea, or early renal dysfunction
• The elevated chloride (106 mmol/L, upper normal) supports a hyperchloremic metabolic acidosis pattern
• Despite the normal creatinine and GFR, subtle renal tubular dysfunction can present with isolated bicarbonate loss 2

BUN - 7 mg/dL

This is below the normal range (typically 7-20 mg/dL). While guidelines note that BUN may be low secondary to low protein intake and may not adequately reflect renal function 3, a BUN of 7 mg/dL combined with low total protein suggests:

• Inadequate protein intake
• Liver synthetic dysfunction (though other liver enzymes are normal)
• Overhydration (though sodium is normal, arguing against this)

Total Protein - 5.8 g/dL

This is below normal range (typically 6.0-8.3 g/dL). With albumin at 3.9 g/dL (lower end of normal 3.5-5.0 g/dL), the globulin fraction calculates to 1.9 g/dL, which is low (normal 2.0-3.5 g/dL) 4.

Clinical implications:

• Mild hypoproteinemia may indicate malnutrition, protein-losing conditions, or chronic disease
• The combination of low BUN and low total protein strongly suggests inadequate protein intake 3

Borderline/Context-Dependent Values

Glucose - 109 mg/dL

While technically within "normal" range (70-100 mg/dL fasting), this represents impaired fasting glucose if obtained in a fasting state, warranting diabetes screening. If non-fasting, this is normal 1.

Calcium - 8.9 mg/dL

At the lower end of normal (8.5-10.5 mg/dL). When corrected for the low albumin (corrected calcium = measured calcium + 0.8 × [4.0 - albumin]), the corrected calcium is approximately 8.98 mg/dL, which remains low-normal 5.

Normal Values Confirmed

All other values fall within standard reference ranges:

• Electrolytes: Sodium 141, Potassium 4.5, Chloride 106 mmol/L (all normal) 6
• Renal function: Creatinine 0.5 mg/dL, GFR >78 mL/min/1.73 m² (normal to excellent) 7, 8
• Liver enzymes: AST 29, ALT 32, Alkaline Phosphatase 80, Bilirubin 0.2 mg/dL (all normal; ALT <33 IU/L for males, <25 IU/L for females is considered truly normal) 9, 10
• Albumin: 3.9 g/dL (low-normal range)

Clinical Pitfalls

• Do not dismiss the low bicarbonate as a laboratory error—this represents true metabolic acidosis requiring evaluation for underlying causes including renal tubular acidosis, GI losses, or medication effects 2
• The normal creatinine does not exclude renal pathology—tubular dysfunction can occur with preserved GFR 3
• Low BUN with normal creatinine specifically points toward nutritional issues rather than renal failure 3
• The combination of low total protein, low BUN, and metabolic acidosis suggests a systemic process requiring comprehensive evaluation including dietary assessment and consideration of chronic disease states