Comprehensive Metabolic Panel with Adjusted Calcium, Plasma

Plasma glucose concentration reflects the dynamic equilibrium between hepatic output, intestinal absorption, and peripheral tissue uptake. Insulin and counter-regulatory hormones tightly govern glucose homeostasis; in fasting states hepatic glycogenolysis and gluconeogenesis maintain supply, while postprandially insulin suppresses hepatic glucose release and drives cellular uptake.

Glucose is the cornerstone marker of glycaemic control and diabetes screening. Fasting plasma glucose ≥7.0 mmol/L (126 mg/dL) or random ≥11.1 mmol/L (200 mg/dL) meets diagnostic criteria for diabetes when confirmed. Impaired fasting glucose (5.6–6.9 mmol/L) signals prediabetes, prompting lifestyle intervention and haemoglobin A1c assessment.

Urea is synthesised in the liver from ammonia generated during amino-acid catabolism, circulates freely, is filtered at the glomerulus, and undergoes variable tubular reabsorption depending on volume status. Its concentration reflects protein turnover, hepatic ureagenesis, glomerular filtration, and renal tubular handling.

BUN is a crude index of renal function but is non-specific; it rises with reduced glomerular filtration, increased protein catabolism, gastrointestinal bleeding, and volume depletion, and falls with liver failure or low protein intake. The BUN:creatinine ratio helps distinguish prerenal azotaemia (ratio typically >20:1) from intrinsic renal disease.

Creatinine is a non-enzymatic breakdown product of muscle creatine phosphate, produced at a relatively constant rate proportional to muscle mass, freely filtered at the glomerulus with minimal tubular reabsorption, and minimally secreted. Its plasma concentration is inversely related to glomerular filtration rate.

Creatinine is the primary marker for estimating glomerular filtration rate via the CKD-EPI or MDRD equations; rising creatinine signals declining renal function. Acute kidney injury criteria incorporate absolute and relative increases; chronic kidney disease staging relies on estimated GFR derived from creatinine, age, sex, and ethnicity.

eGFR is calculated from plasma creatinine using population-based equations (CKD-EPI 2021 recommended) that incorporate age and sex. The 2021 equation removes race coefficients previously embedded in older formulas, aligning with equity and precision goals.

eGFR is the foundation of chronic kidney disease classification: G1 (≥90), G2 (60–89), G3a (45–59), G3b (30–44), G4 (15–29), and G5 (<15 or dialysis). Declining eGFR prompts nephrology referral, medication dose adjustment, and cardiovascular risk stratification. Acute changes in creatinine invalidate eGFR interpretation.

Sodium is the principal extracellular cation, governing plasma osmolality, extracellular fluid volume, and membrane potential. Its concentration is tightly regulated by thirst, renal free-water handling via vasopressin, and aldosterone-mediated tubular reabsorption.

Dysnatraemia is among the most frequent electrolyte disturbances. Hyponatraemia (<135 mmol/L) is classified by volume status and osmolality into hypovolaemic, euvolaemic (often syndrome of inappropriate antidiuresis), and hypervolaemic types. Hypernatraemia (>145 mmol/L) reflects free-water deficit or sodium excess and carries high morbidity if acute or severe.

Potassium is the principal intracellular cation; only 2% circulates in plasma, yet this small extracellular pool critically determines membrane potential and cellular excitability. Renal excretion, regulated by aldosterone and distal tubular flow, is the major route of elimination, while transcellular shifts driven by insulin, acid–base status, and catecholamines rapidly alter plasma concentration.

Hypokalaemia (<3.5 mmol/L) and hyperkalaemia (>5.0 mmol/L) both carry arrhythmia risk; severe hyperkalaemia (>6.5 mmol/L) is a medical emergency. Causes span renal losses, gastrointestinal losses, medication effects (diuretics, ACE inhibitors, potassium-sparing diuretics), and transcellular shifts. Spurious elevation may result from haemolysis or prolonged tourniquet time.

Chloride is the major extracellular anion, moving in parallel with sodium to maintain electroneutrality and plasma osmolality. It also participates in acid–base balance through renal bicarbonate exchange, and hypochloraemia or hyperchloraemia often accompanies metabolic alkalosis or acidosis, respectively.

Chloride is interpreted alongside sodium, bicarbonate, and the anion gap. Hypochloraemia accompanies volume depletion, diuretic use, and vomiting (contraction alkalosis); hyperchloraemia arises in normal-anion-gap metabolic acidosis (diarrhoea, renal tubular acidosis) and iatrogenic saline excess.

Total CO₂ in venous plasma reflects predominantly bicarbonate, with small contributions from dissolved CO₂ and carbonic acid. Bicarbonate is the principal extracellular buffer, regulated by renal reabsorption and regeneration in response to acid–base disturbances; respiratory compensation via CO₂ excretion occurs within minutes, renal compensation over days.

Total CO₂ is the metabolic component of acid–base status. Low bicarbonate (<22 mmol/L) suggests metabolic acidosis or respiratory alkalosis with compensation; elevated bicarbonate (>29 mmol/L) suggests metabolic alkalosis or respiratory acidosis with compensation. Calculate the anion gap and interpret with clinical context and, when needed, arterial blood gas.

Approximately 40% of circulating calcium is bound to albumin, 10% to other anions, and 50% circulates as the physiologically active ionised fraction. Parathyroid hormone, vitamin D, and calcitonin regulate calcium homeostasis through intestinal absorption, renal reabsorption, and skeletal mobilisation.

Total calcium is the routine screening marker for disorders of calcium homeostasis. Hypercalcaemia is most often caused by primary hyperparathyroidism or malignancy; hypocalcaemia arises with hypoparathyroidism, vitamin D deficiency, chronic kidney disease, and hypomagnesaemia. Because albumin concentration affects total calcium, adjustment formulas estimate ionised calcium when albumin is abnormal.

Adjusted calcium applies a formula to correct total calcium for hypoalbuminaemia or hyperalbuminaemia, estimating what the total calcium concentration would be at a standard albumin level (typically 40 g/L or 4.0 g/dL). Common formulas add approximately 0.02 mmol/L (0.8 mg/dL) for every 1 g/dL that albumin falls below 4.0 g/dL.

Adjusted calcium provides a better estimate of ionised (free) calcium status than uncorrected total calcium when albumin is abnormal. It guides decisions about hypercalcaemia or hypocalcaemia work-up, though direct ionised calcium measurement remains the gold standard in critically ill patients or complex acid–base disturbances.

Albumin is the most abundant plasma protein, synthesised exclusively in the liver at a rate influenced by nutritional status, inflammation, and colloid oncotic pressure. It binds calcium, hormones, bilirubin, and many drugs, maintains plasma oncotic pressure, and serves as a negative acute-phase reactant.

Hypoalbuminaemia reflects decreased synthesis (liver disease, malnutrition, inflammation), increased loss (nephrotic syndrome, protein-losing enteropathy, burns), or haemodilution. Low albumin is an independent predictor of poor outcomes in hospitalised patients and chronic disease. It also affects interpretation of total calcium, necessitating correction formulas or ionised calcium measurement.

Total protein is the sum of albumin and globulins (immunoglobulins, acute-phase proteins, complement, and transport proteins). Liver synthesises most proteins; immune cells produce immunoglobulins. Total protein reflects nutritional state, hepatic synthetic function, immune activity, and volume status.

Hyperproteinaemia is usually due to dehydration or monoclonal gammopathy; hypoproteinaemia mirrors hypoalbuminaemia causes but may also reflect hypogammaglobulinaemia. The albumin:globulin ratio adds nuance — a reversed ratio (<1) suggests chronic inflammation, cirrhosis, or myeloma. Total protein is a coarse screen; protein electrophoresis characterises globulin fractions when indicated.

Alkaline phosphatase is a family of isoenzymes expressed in liver (bile canaliculi), bone (osteoblasts), intestine, and placenta. The liver and bone isoforms dominate in adults; elevation reflects increased synthesis or release rather than cellular injury per se.

ALP is the cardinal marker of cholestasis when liver origin is confirmed by concurrent elevation of GGT or bilirubin. Isolated ALP elevation with normal GGT suggests bone pathology — Paget disease, osteomalacia, fracture healing, or bone metastases. Physiological elevations occur in pregnancy (placental isoform) and during adolescent growth spurts.

AST is a mitochondrial and cytosolic enzyme present in hepatocytes, myocardium, skeletal muscle, kidney, and red blood cells. Cellular injury releases AST into plasma; its half-life is shorter than that of ALT, so AST rises and falls more rapidly in acute injury.

AST is less liver-specific than ALT; elevations occur with hepatocellular injury, myocardial infarction, skeletal muscle damage, and haemolysis. The AST:ALT ratio distinguishes aetiologies — a ratio <1 is typical of steatotic liver disease, while >2 suggests alcohol-related injury. In the metabolic panel AST complements ALT and ALP to classify liver injury as hepatocellular versus cholestatic.

ALT is a cytosolic enzyme concentrated in hepatocytes, with much smaller amounts in kidney and muscle. It catalyses transamination between alanine and alpha-ketoglutarate, linking amino-acid and glucose metabolism. Its high hepatic specificity makes it the preferred marker of hepatocellular injury.

ALT elevation signals hepatocellular damage — steatotic liver disease, viral or autoimmune hepatitis, drug-induced liver injury, or ischaemic hepatitis. Mild chronic elevations are the hallmark of metabolic dysfunction-associated steatotic liver disease; very high values (>10× upper limit) suggest acute viral, toxic, or ischaemic injury. Lower healthy thresholds (≤30 U/L in men, ≤19–25 U/L in women) are advocated by some hepatology guidelines.

Bilirubin is the end-product of haem catabolism, predominantly from senescent red blood cells. Unconjugated (indirect) bilirubin is lipophilic and albumin-bound; hepatocyte uptake, conjugation with glucuronic acid, and biliary excretion yield water-soluble conjugated (direct) bilirubin. Total bilirubin is the sum of both fractions.

Elevated total bilirubin (hyperbilirubinaemia) manifests as jaundice when >50 µmol/L (3 mg/dL). The pattern of elevation — unconjugated versus conjugated — narrows the differential: unconjugated predominance suggests haemolysis or Gilbert syndrome, while conjugated hyperbilirubinaemia points to hepatocellular dysfunction or cholestasis. Fractionation into direct and indirect is often needed to guide further investigation.