Nephrology Clinical Laboratory Medicine DrCope 2025 PDF

(slide for Intro drawing) Clinical Laboratory Medicine and the Kidneys Nathan Cope, PharmD, BCPS Assistant Professor of Pharmacy Practice South College School of Pharmacy Learning Objectives Describe the normal physiology of the kidneys and how it relates to handling of substa...

(slide for Intro drawing) Clinical Laboratory Medicine and the Kidneys Nathan Cope, PharmD, BCPS Assistant Professor of Pharmacy Practice South College School of Pharmacy Learning Objectives Describe the normal physiology of the kidneys and how it relates to handling of substances we use to monitor renal function with common laboratory tests Understand the utility, usefulness, and limitations of common laboratory tests and/or equations used to evaluate renal function or etiology of renal dysfunction Be able to estimate creatinine clearance using specifically the Cockcroft-Gault equation if given patient demographics and relevant lab values Know the major components of a urinalysis and what various results in macroscopic, microscopic, and chemical analysis of a urine sample may indicate Appreciate the role a pharmacist plays in patient care when it comes to monitoring and reacting to specific laboratory tests and results involving the kidneys Common Terms and Abbreviations Glomerulus Postrenal Afferent arteriole MDRD (Modification of Diet in Renal Disease) Efferent arteriole GFR (glomerular filtration rate) Loop of Henle Azotemia Distal Convoluted Tubule Erythrocytes Collecting Duct RBC (red blood cells) CKD (chronic kidney disease) Leukocyte BMP (basic metabolic panel) WBC (white blood cells) SCr (serum creatinne) Leukocyte esterase Creatine Casts Creatinine Tubular epithelial cells CrCl (creatinine clearance) Proteinuria Cockcroft-Gault Nitrite BUN (blood urea nitrogen) Specific gravity Prerenal UTI (urinary tract infection) Intrarenal (intrinsic) Bacteriuria Outline Review of Kidney Anatomy and Physiology Renal Assessment – Estimating Function – Serum Creatinine and Cockcroft-Gault – Blood Urea Nitrogen Medications and Renal Elimination Components of a Urinalysis – Macroanalysis – Microanalysis – Chemical analysis Role of the Kidneys Maintain homeostasis Excretion/elimination – water – solutes (electrolytes, metabolic by-products, drugs…) Substance activation and synthesis – regulate blood pressure – regulate metabolism – RBC (red blood cell) production Lee, 2017 Renal Anatomy and Physiology https://my.clevelandclinic.org/health/diseases/15096-kidney-disease-chronic-kidney-disease Renal Anatomy and Physiology, continued Nephron – each kidney contains ~1 million – functional unit of the kidneys Arterioles (afferent and efferent) Glomerulus (Bowmen’s Capsule) Proximal tubule Loop of Henle Distal convoluted tubule Collecting duct – glomerular filtration – tubular secretion – tubular reabsorption Lee, 2017 Renal Anatomy and Physiology, continued https://www.researchgate.net/figure/Composition-of-nephron-tubules-in-health-and-disease-A-Left-Healthy-tubule-with- an_fig4_236922670 Kidney Injury Prerenal – perfusion (blood flow) Renal Plasma Flow ~625ml/min – 20% filtered by glomerulus Glomerular Filtration Rate – ~120ml/min – 180 L/day filtered – only 1% excreted as urine Intrarenal (Intrinsic) – cellular necrosis/inflammation Postrenal – obstruction stones, BPH… Assessment of Kidney Function Markers of Clearance – Exogenous Markers Inulin Clearance I-Iothalamate Cr-EDTA – Endogenous Markers Cystatin C Serum Creatinine Creatinine and timed urine collection Estimation Equations – Cockcroft-Gault equation – GFR-MDRD equation – Cystatin C equations Lee, 2017 Muscle and Serum Creatinine Muscle, Creatine, and Creatinine – creatine and creatine phosphate energy source for muscle – phosporus for ATP regeneration decomposes to creatinine – creatinine is a by-product of muscle – for a given muscle mass, production is constant Serum Creatinine – cleared by the kidneys – creatinine clearance is a surrogate marker for filtration rate – reported in the BMP (basic metabolic panel) Cockcroft-Gault Equation – historical “gold standard” for drug dosing Lee, 2017 Creatinine Clearance (CrCl) Of note, it takes time to reach a new steady state Lee, 2017 Ideal Body Weight (IBW) Cockcroft-Gault Equation ; (if female x 0.85) Appropriate Weight If ABW < IBW, use ABW If ABW ≥ IBW, use IBW unless… If ≥120% of IBW, use adjusted body weight Adjusted Body Weight = [0.4 (ABW-IBW)] + IBW *do not round SCr for elderly patients* In-class Examples 1. Gather Information 2. Calculate IBW 3. Evaluate % of IBW, determine appropriate weight 4. Calculate Adjusted Body Weight (if needed) 5. Perform Cockcroft-Gault Equation (note gender) Example 1 63 yo male Height = 6’ 1” Actual Body Weight = 90 kg SCr 2.1 Example 2 45 yo female Height = 5’ 7” Actual Body Weight = 81 kg SCr 1.3 Example 3 35 yo female Height = 5’ 4” Actual Body Weight = 49 kg SCr 0.7 Blood Urea Nitrogen (BUN) Concentration of nitrogen (as urea) in the serum Urea is renally cleared, but multifactorial – urea production – glomerular filtration – tubular reabsorption Used to monitor – renal function – hydration status – protein tolerance – catabolism Lee, 2017 Blood Urea Nitrogen (BUN), continued Urea reabsorption – parallels water and sodium retention – related to rate of urine flow through tubules Elevated BUN (azotemia) – high protein diet – upper gastrointestinal bleed – drugs with antianabolic effects corticosteroids, tetracyclines – decreased urine flow rate through tubules Decreased BUN – could hint at malnourishment… but other labs more indicative – liver damage Lee, 2017 BUN and Prerenal Injury https://my.clevelandclinic.org/health/diseases/15096-kidney-disease-chronic-kidney-disease BUN and Prerenal Injury (cont) BUN to SCr Ratio Kidney injury due to volume depletion – dehydration – shock heart failure, sepsis, blood loss… Suspected prerenal injury – BUN and SCr elevate creatinine is not reabsorbed in tubules urea is reabsorbed – BUN:SCr >20:1 Suspected intrarenal (intrinsic) injury – BUN: SCr 10:1 to 20:1 Lee, 2017 Renal Function and the Pharmacist Nephrotoxic drugs – monitoring for adverse effects vancomycin-induced nephrotoxicity aminoglycosides, colistimethate, piperacillin/tazobactam, etc… Renally eliminated drugs – renal dose adjustments therapeutic drug monitoring – vancomycin, digoxin, tacrolimus, etc… fixed dose adjustments and protocols – enoxaparin, meropenem, piperacillin/tazobactam, tikosyn, etc… – contraindications fondaparinux and CrCl