13. RENAL AND THYROID FUNCTION TESTS

Renal and thyroid function tests are essential diagnostic investigations used to assess kidney performance and the metabolic activity of the thyroid gland. These tests play a crucial role in diagnosing diseases, monitoring therapy, and evaluating drug effects. Clinical pharmacists must understand the interpretation of these tests to optimize medication therapy, adjust drug dosages, and provide evidence-based recommendations for patient care.

RENAL FUNCTION TESTS

Renal function tests (RFTs) evaluate how effectively the kidneys filter blood, maintain electrolyte balance, and excrete waste products. They help detect acute kidney injury, chronic kidney disease, and drug-induced nephrotoxicity.

1. Blood Urea

Urea is a waste product formed from protein metabolism. It is excreted by the kidneys and used as a marker of renal function.

  • High urea (Uremia): renal failure, dehydration, high-protein diet, GI bleeding.
  • Low urea: liver failure, malnutrition.

2. Serum Creatinine

Creatinine is a breakdown product of muscle metabolism and is a more reliable marker of renal function than urea.

  • High creatinine: kidney dysfunction, nephrotoxic drug exposure, dehydration.
  • Low creatinine: muscle wasting, aging.

3. Blood Urea Nitrogen (BUN) / Creatinine Ratio

This ratio helps differentiate between pre-renal, renal, and post-renal causes of kidney dysfunction.

  • High ratio: dehydration, GI bleed.
  • Low ratio: liver disease, malnutrition.

4. Estimated Glomerular Filtration Rate (eGFR)

eGFR is the most important indicator of kidney function. It estimates the rate at which kidneys filter blood.

  • Normal: >90 mL/min/1.73m²
  • CKD Stage 3: 30–59 mL/min
  • CKD Stage 5 (ESRD): <15 mL/min

eGFR is crucial for dose adjustments of drugs such as antibiotics (e.g., vancomycin), antidiabetics, and anticoagulants.

5. Serum Electrolytes

Kidneys regulate electrolytes essential for nerve and muscle function.

Sodium (Na⁺)

  • Hyponatremia: heart failure, SIADH, renal disease, diuretics.
  • Hypernatremia: dehydration, diabetes insipidus.

Potassium (K⁺)

  • Hyperkalemia: renal failure, ACE inhibitors, potassium-sparing diuretics.
  • Hypokalemia: vomiting, diarrhea, thiazide or loop diuretics.

Chloride and Bicarbonate (HCO₃⁻)

  • Used to evaluate acid–base balance.
  • Low bicarbonate suggests metabolic acidosis, commonly seen in renal failure.

6. Urinalysis

Urinalysis provides valuable information about kidney function and systemic diseases.

  • Proteinuria: glomerular disorders.
  • Hematuria: stones, infections.
  • Glucosuria: uncontrolled diabetes.
  • Casts: RBC casts in glomerulonephritis, WBC casts in pyelonephritis.

7. Creatinine Clearance (CrCl)

An important test to estimate kidney filtration, used for drug dose adjustment.

  • Calculated using Cockcroft–Gault equation.
  • CrCl lower than 60 mL/min indicates renal impairment.

THYROID FUNCTION TESTS

Thyroid function tests (TFTs) assess the production of thyroid hormones, which regulate metabolism, energy production, growth, and development. Abnormal levels indicate conditions such as hypothyroidism, hyperthyroidism, and autoimmune thyroid disorders.

1. Thyroid-Stimulating Hormone (TSH)

TSH is the most sensitive indicator of thyroid function.

  • High TSH: primary hypothyroidism.
  • Low TSH: hyperthyroidism or pituitary dysfunction.

2. Thyroxine (T4)

T4 is the major circulating thyroid hormone.

  • High T4: hyperthyroidism, thyrotoxicosis.
  • Low T4: hypothyroidism, severe illness.

3. Triiodothyronine (T3)

T3 is more active than T4 and important in diagnosing hyperthyroidism.

  • High T3: Graves’ disease.
  • Low T3: chronic illness, hypothyroidism.

4. Free T3 and Free T4

These tests measure unbound hormones and provide more accurate assessments, especially when protein levels vary.

5. Thyroid Antibody Tests

Used to diagnose autoimmune thyroid diseases.

  • Anti-TPO antibodies: Hashimoto’s thyroiditis.
  • TSI antibodies: Graves’ disease.

6. Thyroglobulin

Used in monitoring thyroid cancer recurrence.

7. Radioactive Iodine Uptake (RAIU)

Evaluates iodine uptake by thyroid gland.

  • High uptake: Graves’ disease, toxic nodular goiter.
  • Low uptake: thyroiditis, iodine overload.

Clinical Interpretation

Hypothyroidism

  • High TSH
  • Low Free T4
  • Symptoms: fatigue, weight gain, cold intolerance

Hyperthyroidism

  • Low TSH
  • High T3/T4
  • Symptoms: weight loss, heat intolerance, tremors

Chronic Kidney Disease (CKD)

  • Elevated urea and creatinine
  • Decreased eGFR
  • Electrolyte imbalances (hyperkalemia, acidosis)

Drug-Induced Abnormalities

Nephrotoxic Drugs

  • Aminoglycosides
  • NSAIDs
  • Amphotericin B
  • ACE inhibitors (in renal artery stenosis)

Thyroid-Affecting Drugs

  • Amiodarone: causes hypo- or hyperthyroidism.
  • Lithium: induces hypothyroidism.
  • Antithyroid drugs: carbimazole, methimazole.

Detailed Notes:

For PDF style full-color notes, open the complete study material below:

Share your love