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A 60 year old person old person is suffering from diabetes for last 10 years. a.List the biochemical investigations you should advise him as a part of regular check-up. b.Write down the biochemical reference range of those parameters. c.Explain the alternation of lipid metabolism in diabetes

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Biochemical Monitoring and Lipid Metabolism in a 60-Year-Old with 10-Year Diabetes History

Part A: Biochemical Investigations for Regular Check-Up

A long-standing diabetic (10 years) needs monitoring for glycemic control, end-organ damage (renal, hepatic, cardiovascular), and complications. The recommended panel includes:

1. Glycemic Control

  • Fasting Plasma Glucose (FPG)
  • Postprandial Plasma Glucose (PPPG) - 2 hours after a meal
  • Glycated Haemoglobin (HbA1c) - reflects average glucose over the past 12-14 weeks (lifespan of RBCs)

2. Renal Function (Diabetic Nephropathy Screening)

  • Serum Creatinine
  • Blood Urea Nitrogen (BUN) / Serum Urea
  • Urine Microalbumin / Urine Albumin-to-Creatinine Ratio (UACR)
  • eGFR (estimated Glomerular Filtration Rate) - calculated from creatinine

3. Lipid Profile (Diabetic Dyslipidemia / Cardiovascular Risk)

  • Total Cholesterol
  • LDL-Cholesterol
  • HDL-Cholesterol
  • Triglycerides (TG)

4. Hepatic Function

  • Liver Function Tests (LFTs): ALT, AST, ALP, bilirubin, serum albumin

5. Complete Blood Count (CBC)

  • To detect anaemia (common in diabetic nephropathy) and infection

6. Thyroid Function

  • TSH (type 2 diabetes and hypothyroidism frequently coexist)

7. Urine Examination

  • Urine Routine and Microscopy - for glucosuria, proteinuria, ketonuria
  • 24-hour urinary protein or spot UACR

8. Electrolytes

  • Serum sodium, potassium, bicarbonate (important with renal involvement)

9. Serum Uric Acid

  • Elevated in insulin resistance / metabolic syndrome

Part B: Biochemical Reference Ranges

InvestigationReference / Target Range
Fasting Plasma Glucose70-100 mg/dL (normal); Prediabetes: 100-125 mg/dL; Diabetes: ≥126 mg/dL
2-hr Postprandial Glucose<140 mg/dL (normal); Prediabetes: 140-199; Diabetes: ≥200 mg/dL
Random Plasma Glucose<140 mg/dL (normal); Diabetes diagnosed if ≥200 mg/dL with symptoms
HbA1cNormal: 4.0-5.6%; Prediabetes: 5.7-6.4%; Diabetes: ≥6.5%; Target in treated DM: <7%
Serum Creatinine0.6-1.2 mg/dL (males); 0.5-1.1 mg/dL (females)
Blood Urea Nitrogen (BUN)8-25 mg/dL
Urine Microalbumin<30 mg/g creatinine (normal); 30-300 = microalbuminuria; >300 = macroalbuminuria
Total Cholesterol<200 mg/dL (desirable); 200-239 borderline; ≥240 high
LDL-Cholesterol<100 mg/dL (target in diabetics); <70 mg/dL if CVD risk present
HDL-Cholesterol>40 mg/dL (males); >50 mg/dL (females)
Triglycerides<150 mg/dL (normal); 150-199 borderline; ≥200 high
ALT (SGPT)7-40 U/L
AST (SGOT)10-40 U/L
TSH0.4-4.0 mIU/L
Serum Uric Acid3.5-7.2 mg/dL (males); 2.6-6.0 mg/dL (females)
Sources: Basic Medical Biochemistry - A Clinical Approach 6e (Lieberman); Henry's Clinical Diagnosis and Management by Laboratory Methods

Part C: Alterations of Lipid Metabolism in Diabetes

Insulin plays a central regulatory role in lipid metabolism. In diabetes (especially type 2 with insulin resistance and type 1 with insulin deficiency), this regulation breaks down at multiple levels:

1. Increased Lipolysis in Adipose Tissue

In the insulin-deficient or insulin-resistant state, hormone-sensitive lipase (HSL) in adipocytes is no longer suppressed. This results in:
  • Increased breakdown of stored triglycerides (TG) in adipose tissue
  • Massive release of free fatty acids (FFAs) and glycerol into the circulation
  • FFAs flood the liver and peripheral tissues
"Free fatty acids leave her adipocytes and are converted by the liver to ketone bodies acetoacetic acid and β-hydroxybutyric acid." - Basic Medical Biochemistry 6e

2. Increased Hepatic VLDL Synthesis

The liver receives excess FFAs and, under low insulin signalling:
  • Increased re-esterification of FFAs into triglycerides
  • These TG are packaged and secreted as VLDL particles
  • Result: Hypertriglyceridaemia (elevated serum TG)
"Triacylglycerols, present primarily in chylomicrons and very-low-density lipoproteins (VLDL), would rise in the blood, increasing the likelihood of atherosclerotic vascular disease." - Basic Medical Biochemistry 6e

3. Reduced Activity of Lipoprotein Lipase (LPL)

  • Insulin normally activates lipoprotein lipase (LPL) on capillary endothelium
  • In insulin deficiency/resistance, LPL activity is reduced
  • Chylomicrons and VLDL are not cleared efficiently from the plasma
  • This further compounds hypertriglyceridaemia and chylomicronaemia post-meal

4. Reduced HDL-Cholesterol

  • Low LPL activity means less surface remnants (phospholipids, apolipoproteins) are transferred to HDL during VLDL/chylomicron lipolysis
  • Elevated TG promotes CETP (Cholesteryl Ester Transfer Protein)-mediated exchange: TG moves into HDL while cholesterol esters move out, making HDL triglyceride-rich
  • This TG-rich HDL is rapidly catabolised by hepatic lipase
  • Result: Low HDL-C levels - a cardinal feature of diabetic dyslipidaemia

5. Small Dense LDL Particles

  • Elevated VLDL provides substrate for CETP-mediated lipid exchange with LDL
  • LDL becomes TG-enriched and then has its TG hydrolysed by hepatic lipase
  • Result: Small, dense LDL particles - more atherogenic because they:
    • Penetrate arterial walls more easily
    • Are more susceptible to oxidation
    • Bind less avidly to LDL receptors, prolonging their plasma half-life
"Dyslipidemia typically characterized by hypertriglyceridemia, reduced HDL cholesterol, increased VLDL, and small dense LDL particles." - Brenner and Rector's The Kidney

6. Ketogenesis (Particularly in Type 1 DM / Uncontrolled DM)

  • Excess FFAs in the liver undergo beta-oxidation, generating large amounts of acetyl-CoA
  • When acetyl-CoA exceeds the capacity of the TCA cycle and exceeds oxaloacetate availability, it is diverted to ketone body synthesis (acetoacetate, β-hydroxybutyrate, acetone)
  • This leads to ketonaemia and ketonuria
  • In severe cases: Diabetic Ketoacidosis (DKA)

7. Increased Cholesterol Synthesis

  • In insulin resistance, SREBP-1c and HMG-CoA reductase activity may be paradoxically maintained
  • Hepatic cholesterol synthesis is not adequately suppressed, contributing to hypercholesterolaemia

Summary: The Diabetic Lipid Profile ("Diabetic Dyslipidaemia")

ParameterChange in DiabetesMechanism
Triglycerides↑ (elevated)↑ VLDL synthesis, ↓ LPL activity
VLDL↑ (elevated)↑ hepatic TG synthesis from FFAs
LDL-C (total)Normal or mildly ↑But particle size shifts to dangerous small dense LDL
HDL-C↓ (reduced)↓ LPL activity, ↑ CETP-mediated exchange, ↑ HDL catabolism
Free Fatty Acids↑ (elevated)↑ Lipolysis due to ↓ insulin activity
Ketone bodies↑ (elevated, esp. T1DM)↑ FFA oxidation → excess acetyl-CoA → ketogenesis
This combination of high TG, low HDL, and small dense LDL is highly atherogenic and explains why long-standing diabetics face a 2-4× higher risk of cardiovascular disease.
Key sources: Basic Medical Biochemistry - A Clinical Approach 6e (Lieberman); Guyton and Hall Textbook of Medical Physiology; Brenner and Rector's The Kidney
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