Labs and Mointoring_11-6-23.pdf

LAB VALUES & DRUG MONITORING BACKGROUND Laboratory values assist healthcare providers in diagnosing and monitoring diseases and drug therapies. Blood or other samples can be sent to a hospital or outside laboratory, but there are newer methods. Pojnt-of-care (POC) testing provides rapid results at...

LAB VALUES & DRUG MONITORING BACKGROUND Laboratory values assist healthcare providers in diagnosing and monitoring diseases and drug therapies. Blood or other samples can be sent to a hospital or outside laboratory, but there are newer methods. Pojnt-of-care (POC) testing provides rapid results at the site of patient .~!:s'.· There are many POC tests, including tests for cardiac enzymes, AlC, INR, various infections and others. Home testing kits provide convenience and privacy and are available to test for pregnancy, ovulation, HIV infection, herpes, fecal occult blood and presence of illicit substances or opioids. Many are available OTC. The1•apeutic drug monitoring (TDM) involves obtaining a ~ level or related labs to monitor efficacy and ~afejy. TDM is reviewed in detail at the end of this chapter. Pharmacists in many states can order and interpret lab tests for a variety of purposes, including tests to screen for and diagnose disease, monitor drug levels and lab values, check for medication adherence or screen for drugs of abuse. DEFINITIONS COMPLETE BLOOD CELL COUNT The complete blood count (CBC) is a commonly ordered lab panel that analyzes the white blood cells (wncs), or neutrophils, the red blood cells (RBCs) and the platelets (PLTs). The CBC includes the hemoglobin (oxygen-carrying protein in RBCs) and the hematocrit (the level of RBCs in the fluid component of the blood, or plasma). When a CBC_ with differential is ordered, the types of neutrophils are analyzed. RBCs have an average life span of 120 days. Platelets have an average life span of 7 -10 days. 73 4 I LAB VA LUE S & DRUG MO NITOR IN G BASIC METABOLIC PANEL/COMPREHENSIVE METABOLIC PANEL The basic metabolic panel (BMP) includes seven to eight tests that analyze electrolytes, glucose, renal function and acid/base (with the HC03, or bicarbonate). Some labs calculate and report the anion gap along with the BMP (see Calculations IV chapter). A comprehensive metabolic panel (CMP) includes the tests in the BMP plus albumin, alanine aminotransferase (ALT), aspartate aminotransferase (AST) , total bilirubin and total protein. The additional tests are used primarily to assess liver function. The BMP and CMP are groups of labs that are ordered together for convenience. The stick diagrams below are used in practice when writing a paper chart note to denote the primary components of the CBC or BMP. Pharmacists should know which values are contained in the stick diagrams below. Hgb wee PLT Hct _N _:--1-H -:-~--1-:-~-:-< 3 Glucose BLOOD CELL LINES Stem cells in the bone marrow produce red blood cells, white blood cells and platelets (see figure). White blood cells can be called leukocytes, and red blood cells can be called erythrocytes. An immature red blood cell is called a reticulocyte (discussed in the Common Laboratory Reference Ranges table) . Changes in Blood Cell Lines Increase 111 l11d1vidl1al Cell Lines iWBC Leukocytosis iRBC Polycythemia i Platelets Thrombocytosis ... Blood Cell Unes Red Blood Cells • 4 Erythrocytes - Dec reJse ,n lnd ividu.11 Ce ll L,nes \, ' J,.wsc Leukopenia J,. RBC (or J,. Hgb) Anemia J,. Platelets Thrombocytopenia Neutrophils White Blood Cells Decre.1se ,n Multipl e Cell Lines Myelosuppresslon • J,. WBC, RBC and platelets Agranulocytosls Drug causes: clozapine, propylthiouracil, methimazole, procainamide, carbamazepine, sulfamethoxazole/ trimethoprim and isoniazid •• Basophils :. •• •• Lymphocytes Monocytes J,. granulocytes (WBCs that have secretory granules in the cytoplasm); includes J,. neutrophils, basophils and eosinophils Platelets Thrombocytes LAB RESULTS 74 Lab results are usually reported as a numerical value (e.g., sodium= 139 mEq/L). Some are reported as "positive" or "negative" or indicate a specific item, such as "Gram-positive cocci." Reference ranges can vary slightly from one facility to another (due to slight variances in products and techniques) and between pediatric and adult populations. A patient's lab results may be within the reference ranges (normal) or outside of the reference ranges (can indicate a serious condition that needs to be addressed rapidly). A value that is termed critical can be life-threatening unless corrective action is taken quickly. The Joint Commission requires that all accredited facilities create and follow a protocol to identify and report critical values to the responsible healthcare provider, who has an established time frame to manage the result. This applies to critical lab values and diagnostic procedure results. Rx PREP 2022 COURSE BOOK I Rx PREP ©2 0 2 1, ©2022 COMMON LABORATORY REFERENCE RANGES - ADULT Reference ranges for labs are generally provided on NAPLEX, but may not be provided on the California Practice Standards and Jurisprudence Exam (CPJE). Familiarity with lab tests and their interpretation will greatly reduce the time required to evaluate cases on the exam. "Must know" labs for pharmacists are bolded in the table, though others are likely to be included in patient cases. The reference range for a healthy adult is provided unless otherwise noted. Drugs specifically indicated to treat a lab abnormality (e.g., urate lowering therapies) are included in the respective chapter (e.g., the Gout chapter). Studying this table will be much easier after mastering all of the associated disease state chapters in this book. ITEM COMMON REFERENCE RANGE NOTES Calcium, total 8.5- 10.5 mg/dl Calcium, ionized 4.5-5.1 mg/dl Calculate corrected calcium if albumin is low (see Calculations Ill chapter for formula). Correction is not needed for ionized calcium. BMP and Electrolytes t due to calcium supplementation, vitamin D, thiazide diuretics. (Cal J. due to long-term heparin, loop diuretics. blsp hosphonates, cinacalcet, systemic steroids, calcitonin, foscarnet. topiramate. Chloride (Cl) Magnesium (Mg) Phosphate (P04) Potassium (K) Supplement calcium in pregnancy, osteoporosis/osteopenia and with certain drugs (see Dietary Supplements, Natural & Complementary Medicine chapter). --- --+-- 95 - 106 mEq/ L Used with other labs to assess acid -base status and fluid balance. 1.3-2.1 mEq/L t due to magnesium-containing antacids and laxatives with renal impairment. J J. due to PPls, diuretics, amphotericin B, foscarnet, echinocandins, diarrhea, chronic alcohol intake. --------11-- t in renal failure. 2.3- 4.7 mg/dL J. due to phosphate binders, foscarn et, oral calcium intake. I 3.5- 5 mEq/L t due to ACE inhibitors, ARBs, aldosterone receptor antagonists (ARAs), alisklren, canagll flozin, cyclosporlne. tacrolimus, mycophenolate, potassium supplements. sulfameU,oxazole/trimethoprim, drospirenone containing oral contraceptives, chronic heparin use, NSAIDs, pentamidine. J. due to beta-2 agonlsts, diuretics, Insulin, steroids, conivaptan, mycophenolate (both t and J. reported). Sodlum(Na) 135-145 mEq/L ~ I~ ue to hypertonic saline, tolvaptan, conivaptan . to ca rbamazepine, oxcarbazepine, SSRls, diuretics, desmopressin. Bicarbonate Venous : 24-30 mEq/L Used to assess acid-base status. (HC03 or "bicarb") Arterial: 22-26 mEq/L t due to loop diuretics, systemic steroids. (varies by method) J. due to topiramate, zonisamide, salicylate overdose. Blood Urea Nitrogen 1 7-20: /dl (BUN) Serum Creatinlne (SCr) 0.6-1.3 mg/ dl ------- tin renal impairment and dehydration. Used with SCr (e.g., BUN:SCr ratio) to assess fluid status and renal function. t due to many drugs that impair renal function (e.g., amlnoglycosides, amphotericln B. cisplatin, colistimethate, cyclosporine, loop diuretics, polyrnyxln, NSAIDs, radlocontrast dye, tacro!imus, vancomycin). False t due to sulfamethoxazole/trimethoprim, H2RAs, cobicistat. J. with low muscle mass, amputation, hemodilution. Anion Gap (AG) -----------+5-12 mEq/L A calculated value, but often reported on the BMP (see Calculations IV chapter) . Presence oft anion gap suggests metabolic acidosis. 75 4 I LAB VALUES & DRU G MONITORING ITEM COMMON REFERENCE RANGE NOTES WBC and Differential Many drugs (including chemotherapy, immunosuppressants and antivirals) have the potential to affect WBC, Hgb and PLTs. White Blood Cells Used to diagnose and monitor infection/inflammation. Can i as an acute phase reactant, indicating a systemic reaction to inflammation or stress (e.g., surgery). 4,000-11,000 cells/mm 3 (WBC) i due to systemic steroids, colony stimulating factors, epinephrine. J, due to clozapine, chemotherapy that targets the bone marrow, carbamazeplne, cephalosporins, immunosuppressants (e.g., DMARDs, biologics), procainamide. vancomycin. Neutrophils 45-73% Bands 3-5% Neutrophils and bands are used with clinical s/sx to assess likelihood of acute infection and with WBC in absolute neutrophil count (ANC) calculation (see Calculations IV chapter). Neutrophils are also ca lled polymorphonuclear cells (PMNs or~) and segmented neutrophlls (segs). Bands are immature neutrophils released from bone marrow to fight infection (called a "left shift" when elevated). Eoslnophils i in drug allergy, asthma, inflammation, parasitic infection. i in viral infections, lymphoma. -----------------------1' in inflammation, hypersensitivity reaction, leukemia. Basophils Lymphocytes 20-40% J, in bone marrow suppre sion, HIV or due to systemic steroids. 1' due to erythropoiesis-stimulating agents (ESAs), smoking and (RBC) polycythemia (a condition that causes high RBCs). 6 Females: 4.1-4.9 x 10 cells/µL J, due to chemotherapy that targets the bone marrow, low production, blood loss, deficiency anemias (e.g., 812, folate), hemolytic anemia, sickle cell anemia. Hemoglobin Males: 13.5- 18 g/dl (Hgb,Hb) Females: 12-16 g/dl Hematocrit Males: 38-50% (Hct) Females: 36-46% Mean Corpuscular Volume 80-100 fl Hgb is the iron-containing protein that carries oxygen in the RBCs. The Hct mirrors the Hgb result (providing the same clinical information). 1' due to ESAs (see Anemia chapter). J, in anemias and bleeding (risk with anticoagulants, antiplatelets, fibrinolytics). See Coombs Test and G6PD for drug-induced anemias. 1' due to B12 or folate deficiency. J. due to~ deficiency. (MCV) Mean Corpuscular Hemoglobin (MCH) 26-34 pg/cell ----1-------------31-37 g/dl Mean Corpuscular Hgb Concentration (MCHC) RBC Distribution Width 11.5-14.5% (ROW) Iron 65-150 mcg/dl Total Iron Binding Capacity 250-400 mcg/dl l itional tests used in an anemia workup. Together MCV, MCHC and Ware called "RBC indices." RD W measures the variability in the RBC size. 1' due to iron supplementation. J, due to blood loss or poor nutritional intake. (TIBC) 76 Transferrin > 200 mg/dl Transferrin Saturation Males: 15-50% (TsAn Females: 12-45% Ferritin 11-300 ng/ml Erythropoietin 2-25 mlU/mL Monitored as part of the workup and treatment for iron deficiency anemia, anemia of chronic disease or anemia of chronic kidney disease (CKD). Often parenteral iron is required in conjunction with an ESA for patients on dialysis (see Anemia chapter). RxPREP 2022 CO UR SE BOOK I Rx PREP ©2021, © 2 022 ITEM COMMON REFERENCE RANGE NOTES Follc acid (folate) 5-25 mcg/L 812 and folate are ordered for further workup of macrocytic anemia. -1, due to phenytoin/fosphenytoin, phenobarbital, primidone, methotrexate, sulfamethoxazole/trimethoprim, sulfasalazine. Supplement folate in women of childbearing age and alcoholism (see Dietary Supplements, Natural & Complementary Medicine chapter). Vitamin B12 > 200 pg/ml -1, due to PPls, metformin, colchicine, chloramphenicol. Methylmalonate Varies Used for further workup of macrocytic anemia when 812 deficiency is suspected. Schilling test has also been used. Retlculocyte count 0.5-2.5% Measures the amount of reticulocytes (immature red blood cells) being made by the bone marrow; reticulocyte count is i in blood loss and -1, in untreated anemia due to iron, folate or 812 deficiency and with~ marrow suppression. Coombs Test, Direct Negative Used in the diagnosis of hemolytic anemia, when the cause of hemolysis is unclear (i.e., an immune mechanism vs. another cause). See Anemia chapter. (MMA) Also known as: Direct Antiglobulin Test (DAT) Drugs that can cause hemolytic anemia include penicillins and cephalosporins (prolonged use/high concentrations), dapsone, isoniazid, levodopa, methyldopa, methylene blue. nitrofurantoin. pegloticase, primaguine, quinidine, quinine, rasburicase, rifampin and sulfonamides. If the Coombs test is positive and a drug-induced cause is suspected, discontinue the offending drug. Glucose-6-phosphate dehydrogenase ---------------- 5-14 units/gram Used to determine if hemolytic anemia is due to G6PD deficiency (the result will be low). (G6PD) I The R8C destruction with G6PD deficiency is triggered by stress, foods (fava beans) or these drugs: dapsone, methylene blue, nitrofurant oin, pegloticase, primaguine, rasburicase, sulfonamides (see Anemia chapter). Anticoagulation These tes ts monitor ctiff PrPnt as11ccts of clotting and arc usc•ct to monitor specific dru gs. Antlfactor Xa Activity 1.0-2.0 IU/ml (therapeutic LMWH) (Antl-Xa) Obtain a peak anti-Xa 4 hours after SC LMWH dose for proper interpretation Used to monitor low molecular weight heparins (LMWHs) and unfrac tionated heparin (UFH). Monitoring for LMWH is recommended in pregnancy and possibly in obesity, low body weight, pediatrics, elderly, renal insufficiency (see Anticoagulation chapter). i Prothrombin Time/ International Normalized Ratio PT: 10-13 seconds (varies) due to heparin, LMWHs, fondaparinux. ----½--- Used to monitor warfarin. INR i (without warfarin) due to liver disease. INR: < 1.2 (for those not on warfarin) False (PT/ INR) i from daptornycin, oritavancin, telavancin. Many drugs Activated Partial Thromboplastln Time (aPTT or PTT) 1 or -1, INR (see Anticoagulation chapter). Used to monitor unfractionated heparin (UFH) and direct thrombin inhibitors (e.g., argatroban). Treatment goal (on UFH): 1.5-2.Sx control False 70-180 seconds (varies) Used to monitor anticoagulation in the cardiac catheterization lab during percutaneous coronary intervention (PCI) and in surgery. -- - -------+-Activated Clotting Time i 22 - 38 seconds (varies, this is called the "control ") -- _________ (ACT) - Platelets 150,000-450,000/mm 3 - (PLTs) i from oritavancin, telavancin. _______ .,_ -------- Platelets are required for clot formation. Spontaneous bleeding can occur when platelets are< 20,000/mm 3 • -1, due to heparin. LM W Hs, fondaparinux, glycoprotein lib/Illa receptor antagonists, linezolid, valproic acid, chemotherapy that targets the bone marrow, rarely other drugs. Heparin -induced platelet antibodies: 1st ELISA test, then 2"d Serotonin release assay (SRA) Negative Heparin-induced thrombocytopenia (HIT) is a platelet drop> 50% from baseline as a result of treatment with UFH or LMWH. Antibody testing is used to confirm diagnosis of HIT. If the ELISA test is positive, a positive SRA is confirmatory. 77 4 I LA B VALUES & DRU G M O NITOR IN G ITEM COMMON REFERENCE RANGE NOTES 3.5-5 g/dl .J, due to cirrhosis and malnutrition. - Liver and Gastroenterology Albumin Serum levels of highly protein-bound drugs (e.g., warfarin, calcium, phenytoin) are impacted by low albumin. Ph enytoln, valproic acid and calcium serum concentrations require correction for low albumin (see Seizures/Epilepsy, Pharmacokinetics and Calculations Ill chapters). A "free" drug level does not require adjustment. l 33-131 IU/ L Alkaline Phosphatase Used with other labs to assess liver, biliary tract (cholestatic) and bone disease. (Alk Phos or ALP) 10-40 units/L Aspartate Aminotransferase - - -- AST and ALT are enzymes released from injured hepatocytes (liver cells). Numerous medications and herbals can Liver Disease chapter). (AST) Alanine Aminotransferase i AST and ALT (see Hepatitis & 10-40 units/L (ALT) Used with other labs to assess liver, biliary tract (cholestasis) and pancreas. Gamma--G - lu-ta_m _y_l_-_ _ 1 9-58 units/L Transpeptidase (GGT) Billrubin, total 0.1-1.2 mg/dl Used along with other liver tests to monitor drug toxicity, determine other causes of liver damage and detect bile duct blockage. 19-60 mcg/dl Though not diagnostic, often measured in suspected hepatic encephalopathy (HE). (TBili) Ammonia i due to valproic acid, topiramate . .J, due to lactulose. Hepatic (liver) panel See above A group of liver function tests (LFTs) ordered together to assess acute and chronic liver inflammation/disease and in baseline and routine monitoring for hepatotoxic drugs. The panel can include other tests to evaluate liver function (e.g., PT/INR, total protein). Males: 55-170 IU/L To assess muscl e inflammati on (myositis) or more serious muscle damage and to diagnose cardiac conditions. AST, ALT, Tbili, Albumin and Alk Phos Creatine Kinase or Creatlne Phosphoklnase Females: 30-135 IU/L i due to daptomycin, quinupristin/dalfopristin, statins, fibrates (especially if given with a statin), emtricitabine, tenofovir, tipranavir, raltegravir, dolutegravir. (CKorCPK) CK-MB isoenzymes, total 6.0 ng/ml As a group, these are called "cardiac enzymes:• CK-MB, TnT and Tnl are used in the diagnosis of Ml. Troponins can be elevated with a few other conditions (e.g., sepsis, PE, CKD). 0-0.1 ng/ ml (assay dependent) TroponinT (TnT) ----------Troponin I ---------1 0-0.5 ng/ml (assay dependent) BNP and NT-proBNP are both markers of cardiac stress. They are not heart failure (HF) nor heart disease-specific, but higher values indicate a (Tnl) _higher likelihood of HF when consistent with HF symptoms. Renal failure _ _ _ _ _ _ _ _ _ __.._ _ _ _ _ _ _ _ _ _ _ _ _ ____, is the second most common cause of i BNP and NT-proBNP. B-Type Natrluretic Peptide < 100 pg/ml or ng/L (BNP) Myoglobin and CK-MB are not interchangeable; they are two separate --------------1--------------------1 markers. Myoglobin is a sensitive marker for muscle injury but has N-Terminal-ProBNP Males:< 61 pg/ml relatively low specificity for acute Ml and therefore is not routinely used for diagnosis (see Acute Coronary Syndrome chapter). (NT-proBNP) Femal es: 12- 151 pg/ml ------~ ' -- - -- Eosinophil count < 100 cells/mcl --------l.--~--- 78 --------- ----- - - Respiratory --- Used to determine if inhaled corticosteroids (ICS) will be beneficial in COPD treatment, along with history of COPD exacerbations (See Chronic ~ structive Pulmonary Disease chapter). RxPREP 2022 COURSE BOOK ITEM COMMON REFERENCE RANGE (TC) I RxPREP ©2021, ©2022 NOTES Fasting begins 9-12 hours prior to lipid blood draw. l Non-HDL = TC - < 100 mg/dL desirable Low Density Llpoproteln (LDL) High Density Lipoproteln < 40 mg/dl, low (male) I (HDL) Non-HDL 60 mg/d desirable < 130 mg/dl, desirable t Triglycerides (TG) < 150 mg/dl [,~abo,e Lipid panel 1 -;;.oup of labs ordered together to assess the major cholesterol types determine cardiovascular risk. A fasting lipid panel is preferred. _ _ TC, HDL, LDL, TG Lipoprotein-a, Lp(a) < 10 mg/dl Apoliprotein-B, Apo B < 130 mg/dl C-reactive Protein 6 HDL. Guidelines do not support specific TC, HDL orTG goals; they support a statin intensity level for LDL-C reductions based on those most likely to benefit. This means that the target values are not being used as goals for treatment, but elevations should be recognized. In some individuals, additional treatment is considered if LDL 70 mg/dl. i Lp(a) and i ApoB are being used more commonly; these are associated with i coagulation and i risk of CVD. i CRP indicates inflammation, which could be due to many conditions (infection, trauma, malignancy). Higher levels indicate i risk. Highsensitivity CRP (hs-CRP) is more sensitive for CVD. 0.5 mg/dl (CRP) Coronary Artery Calcium score 00 Agatston units or< 75 th percentile for age, sex and ethnicity; higher score indicates a higher risk The coronary artery calcium score measures calcium build-up in the coronary arteries. Ankle Brachia! Index 1-1.4 The ankle brachia I index measures the ratio of the BP in the lower legs to the BP in the arms. It is used to assess severity of peripheral artery disease (PAD). An ABI < 1 indicates some degree of PAD. (ABI) Diabetes Fasting Plasma Glucose 126 mg/dl is positive for diabetes (FPG) 100-125 mg/dl is positive for pre-di~betes Hemoglobin A1C < 7% (ADA), ,.:; 6.5% (AACE) (A1C) Estimated Average Glucose ----- < 154 mg/dl (ADA) (eAG) Preprandial blood glucose 80-130 mg/dl(ADA), < 110 mg/dl (AACE) Postprandial blood glucose < 180 mg/dl (ADA), < 140 mg/dl (AACE) C-peptide (fasting) Fasting is 8 hours. See Diabetes chapter for complete discussion and medications that can cause hyper and hypoglycemia. J Average blood glucose over the past 3 months; based on attachment of glucose to hemoglobin; i glucose= i BG attached to Hgb = i A1C. Used to correlate a finger stick glucose with an A1C; an eAG of 126 mg/dLcorresponds to an A1C of 6%. Blood glucose measurement taken before a meal. ---------.--Blood glucose measurement taken after a meal (1-2 hours after the start r Urine Albumin to Creatinine Ratio or Albumin to Creatinine Ratio .18-=:-1.89 ngtmC- Males:< 17 mg/gram of eating). I Insulin breakdown product used to evaluate beta-cell function (distinguish :'.'._Pe 1 from lype 2 diabetes). J, or absent in type 1 diabetes. See Diabetes and Renal Disease chapters. Females: < 25 mg/gram (UACR or ACR) or Urinary Albumin Excretion (UAE) < 30 mg/24 hours L_ ------ 79 4 I LAB VALUES & DRUG MONITORING ITEM COMMON REFERENCE RANGE NOTES Thyroid Function I Thyroid Stimulating Hormone TSH is used with FT4 to diagnose hypothyroidism and is used alone (sometimes with FT4) to monitor patients being treated. 0.3-3 mlU/l i TSH = hypothyroidism, ! TSH = hyperthyroidism. (TSH) i or J, due to amiodarone, interferons. i (hypothyroidism) due to tyrosine kinase inhibitors, lithium, carba mazeplne. Total thyroxine (T4) 4.5-10.9 mcg/dl - 1 - -- - - - - - - - -- - - - l T4 and FT4 are two of several tests used for a detailed assessment of thyroid function (see Thyroid chapter for additional interacting drugs). 0.9-2.3 ng/dl Free thyroxine (FT4) Uric Acid/Gout Uric acid I Males: 3.5-7.2 mg/dl Used in diagnosis/treatment of gout. Females: 2-6.5 mg/dl i due to diuretics, niacin, low doses of aspirin, pyrazinamide, cyclosporine, tacrolimus, select pancreatic enzyme products, select chemotherapy (tumor lysls syndrome). Inflammation/Autoimmune Disease I Normal: 0-0.5 mg/dl C-Reactive Protein Nonspecific tests used in autoimmune disorders. inflammAtion, infections. (CRP) High risk: > 3 mg/dl Rheumatoid Factor, serum Negative, or$ upper limit of normal (ULN) for the lab (usually< 20 IU/ml) If ANA is positive, histone antibody and anti-dsDNA tests will help (RF) Females: $ 30 mm/hr (ESR) Antinuclear Antibodies ---I -7 Drug-induced lupus erythematosus (DILE) can be caused by many drugs. More likely with antl -TNF agents, hydralazine, isonia2id, methimazole, methyldopa, minocycllne, procainamide, propylthiouracll, guinldine, terbinafine. The causative drug must be discontinued (see Systemic Steroids & Autoimmune Conditions chapter). Negative (titers may be provided) (ANA) Antihistone Antibodies Negative (Detected by ELISA) CD4+ T Lymphocyte Count 800-1,100 cells/mm 3 HIV RNA Concentration Undetectable HIV Antibody (Ab) I Males: $ 20 mm/hr Erythrocyte Sedimentation Rate (Viral Load) I establish diagnosis. __ J Used to assess HIV and monitor treatment (see HIV chapter). Measured in copies/ml Negative (non-reactive) HIV DNAPCR Negative HIV p24 Antigen Undetectable I Detects infection with the virus; may not becom-;positive until sever-al- weeks after exposure. Useful for early detection. Acid-Base (Arterial Sample) pH 7.35-7.4_5 _ _ _ _ _ _ _ _ _ _-. Together these values make up an arterial blood gas (ABG). This blood , must be drawn from an artery (not a vein, as with other labs). pCO2 _35-45 mmHg 1 - - - - - - - - - ~1 Often written in chart notes with a stick diagram: pH/ pCO21pO2/HC03/ pO2 80-100 mm Hg 02 Sat (see Calculations IV chapter for ABG interpretation). Bicarbonate I on the ABG is a calculated value, and reference range may differ from HC03 22-26 mEq/l venous samples. I 02 Sat 1 _ >95% -'- 80 -- RxPREP 2022 COURSE BOOK COMMON REFERENCE RANGE ITEM I RxPREP ©2021, ©2022 NOTES Hormonal r Males: 300-950 ng/dl Testosterone total, free < 4-ng/;L Prostate-Specific Antigen (PSA) Human Chorionic Gonadotropln i with testosterone supplementation. -------+-C_a_ n _i _w_i-th_ t_e-st- osterone supplementation. Used in detecting prostate cancer and BPH. --------+ Tested in blood or urine to determine pregnancy. A positive value in a female indicates she is pregnant. Varies by test l (hCG) Lutelnizing Hormone ises mid-cycle, causing egg release from the ovaries (ovulation). Va,;~ d,riag cyde (LH) Tested in urine with ovulation predictor kits for women attempting ] regnancy. Varies Used in evaluation of parathyroid disorders, hypercalcemia and chronic kidney disease (CKD) (see Renal Disease chapter). Cosyntropin Stimulation Test Baseline and timed increase are measured Used to test for adrenal suppression; medications that affect baseline cortisol or suppress adrenal response will impact test and may need to be held prior (e.g., steroids). Lactic acid (lactate) 0.5-2.2 mEq/L Lactic acidosis indicates anaerobic metabolism, which occurs in longdistance running and in certain medical conditions (e.g., sepsis). Parathyroid Hormone (PTH) Other i due to NRTls (see HIV chapter), metformin (low risk/mostly with renal disease and heart failure), alcohol, cyanide. Procalcitonin Prolact;, 0.15 ng/ml J 1-25 ag/ml _ _ _ _ _ __ i due to systemic bacterial infections or severe localized infections. ecretion is regulated by dopamine; can i with haloperidol, risperidone, paliperidone, methyldopa. an J, with bromocriptine. Purified Protein Derivative or Mantoux test (PPD) Rapid Plasma Reagin -- TB skin test (TST) administered by intradermal injection. Not used alone for diagno$is of active TB. Response is measured by diameter (mm) of induration at 48-72 hours (see ID II: Bacterial Infections chapter for interpretation of the PPD). Negative Antibody test used to screen for syphilis. If the RPR is positive, confirmatory testing is performed. Titers may be reported and are used to monitor response to therapy. 275-290 mOsm/kg H2O Used with Na, BUN/SCr, and clinical volume status to evaluate hypo/ hypernatremia. (RPR) Serum osmolality -- No induration (raised area); induration is measured for diagnosis of TB exposure -------- i due to mannitol, toxicities (e.g., ethylene glycol, methanol, propylene glycol). Thiopurine Methyltransferase <': 15 units/ml Those with genetic deficiency of TPMT are at i risk for myelosuppression (bone marrow suppression) and may require lower doses with azathioprine and mercaptopurine. > 30 ng/ml J, levels increase risk of osteoporosis, osteomalacia (rickets), CVD, diabetes, hypertension, infectious diseases and other conditions. (TPMT) Vitamin D, serum 25(0H) Supplement vitamin D with various conditions and drugs (see Dietary Supplements, Natural & Complementary Medicine chapter). ASSESSING PATIENT CASES QUICKLY Cases can be evaluated more quickly by recognizing lab patterns and signs and symptoms that provide a clue to the patient's diagnosis. Watch for drug-induced signs/symptoms and lab changes_ Look for lab contraindications to drugs (e.g., +hCG, hyperkalemia). Additional information can be found in the chapters on these disease states. Lab patterns and likely diagnoses can be located in the first chapter of this Course Book. Lab patterns due to an infectious disease can be found in the Infectious Diseases chapters. 81 4 I LAB VA LUE S & DR UG M ON ITO RIN G THERAPEUTIC DRUG MONITORING Drug levels or other values (such as anti-Xa levels for LMWHs) are used to reach dosing goals and avoid toxicity. Therapeutic drug monitoring (TDM) is increasingly common due to the need to target highly resistant organisms and dose medications properly in overweight and obese patients. The peak level is the highest concentration in the blood the drug will reach and requires time for the drug to distribute in the body's tissues. The trough level is the lowest concentration the drug will reach in the blood and is dt·awn right before the next dose or some short period of time before the next dose (30 minutes is common). This allows time to assess the level before another dose is given and time to hold the next dose if the level is high. The time that drug levels are drawn is critical for accurate interpretation. For example, a tobramycin level of 6 mcg/mL would be interpreted differently if the level was a trough versus a peak. Obtaining drug levels at steady state is often (but not always) preferred. See Pharmacokinetics chapter for further discussion. Narrow therapeutic index (NTI) drugs have a narrow separation between the subtherapeutic (low), therapeutic (desired) and supratherapeutic (high) drug levels. Supratherapeutic drug levels can be toxic. TDM is commonly performed by pharmacists. The following Key Drugs Guy lists drugs that are routinely monitored. These drugs and usual therapeutic ranges are felt to be essential fo1• NAPLEX. THERAPEUTIC DRUG LEVELS DRUG USUAL THERAPEUTIC RANGE Carbamazepine 4-12 mcg/ mL l 0.8-2 ng/ mL (AFib) lJigoxin 0.5-0.9 ng/ mL (HF) Peak: 5- 10 mcg/mL Gentamicin (traditional dosing) I Trough: < 2 mcg/ mL j 0.6-1.2 mEq/L (up to 1.5 mEq/ L fo~acute symptoms), drawn a; a trough Lithium Phenytoin / Fosphenytoin 10-20 mcg/ mL; if albumin is low, correct serum level; see Seizures/ Epilepsy chapter Free Phenytoin 1-2.5 mcg/mL 1 4-10 mcg/mL NAPA (procainamide active 15-25 mcg/ mL Procainamide - ---------- ---------------- metabolite) Combined - Theophylline Tobramycin (traditional dosing) 10-30 mcg/ mL 7 -- 5-15 mcg/mL Peak: 5- 10 mcg/ mL Trough:< 2 mcg/mL Valproic acid 50-100 mcg/mL (up to 150 mcg/mL in some patients); if albumin is low, correct serum level; see Seizures/Epilepsy chapter Vancomycin* Trough: 15-20 mcg/mL for most serious infections (pneumonia, endocarditis, osteomyelitis, meningitis, and bacteremia) Trough: 10- 15 mcg/ml for others Warfarin Goal INR is 2-3 for most indications, use higher range (2.5-3.5) for high-risk indications, such as mechanical mitral valves 'AUC can be used to monitor vancomycin. Refer to the Pharmacokinetics chapter for detailed information. Select Guidelines/References Lab Tests Online. https://labtestsonline.org (accessed 2021 M ar 17). Lee M . Basic Skills in Interpreting Laboratory Data. 6 th ed. Betheseda, MD: ASHP; 2017. Schmidt J, Wieczorkiewicz J. Interpreting Laboratory Data: A Point-of-Care Guide. Betheseda, MD: ASHP; 2012. 82