Top 10 Common Lab Tests Explained, What They Check and How to Prepare

Niugini Medical & Diagnostic Services supports local residents and visitors in Port Moresby with general medical care and clear, practical medical laboratory information. Lab tests can feel confusing, especially when you are unwell, traveling, or managing a long term condition. This guide explains ten of the most commonly ordered lab tests, what they check, what the results can mean, and how to prepare so your results are accurate and useful.

Important note: This article is educational and not a substitute for medical advice. Always follow the instructions given by your clinician or the laboratory, because preparation can vary depending on your condition, medications, and the specific method used by the lab.

How to use this article

• Read the “What it checks” section to understand why the test is requested.
• Use the “How to prepare” section to avoid common mistakes that can change results.
• Keep a list of medicines and supplements you take, including herbal products and vitamins, and share it at your appointment.
• Ask for your report and discuss it with a clinician who knows your symptoms and history. Lab numbers are most meaningful in context.

Before any blood or urine test, do these simple preparation steps

• Confirm fasting requirements, ask whether you should fast for 8 to 12 hours, or if water is allowed. In many cases, plain water is encouraged.
• Hydrate normally unless told otherwise. Dehydration can affect kidney markers and make blood collection harder.
• Avoid heavy exercise for 24 hours if possible. Strenuous activity can temporarily change muscle and liver related measurements.
• Avoid alcohol for 24 to 48 hours unless your clinician advises differently, alcohol can alter liver enzymes, triglycerides, and glucose control.
• Tell the lab if you are pregnant, or if you recently had surgery, an infection, or dehydration. Normal ranges can shift.
• Do not stop prescribed medications unless your clinician specifically instructs you to. Instead, report what you took and when.
• If you are a tourist, mention recent travel, unusual foods, water sources, and any preventive medicines you may be taking.

Top 10 Common Lab Tests Explained, What They Check and How to Prepare

1) Full Blood Count, FBC or CBC

What it checks

• Red blood cells and hemoglobin, to evaluate anemia and oxygen carrying capacity.
• White blood cells, to look for infection, inflammation, immune disorders, and some blood cancers.
• Platelets, which help blood clot, important for bruising, bleeding risk, and monitoring some medications.
• Red cell indices such as MCV and MCH, which help classify anemia types, for example iron deficiency versus vitamin deficiency.

Why clinicians order it

• When you have fatigue, weakness, shortness of breath, dizziness, or pale skin.
• When there is fever, persistent cough, recurrent infections, or body aches.
• Before surgery, during pregnancy checks, or for ongoing monitoring of chronic illness.

How to prepare

• No fasting is usually required. However, if the FBC is ordered with fasting tests like lipids or glucose, you may need to fast.
• Drink water beforehand to make veins easier to access.
• Tell your clinician about recent bleeding, heavy menstrual periods, blood donation, or iron supplements, these can affect results.
• Report recent infections, vaccines, or steroid use, these can change white cell counts.

How to interpret common patterns

• Low hemoglobin may suggest anemia from iron deficiency, chronic disease, blood loss, or vitamin B12 or folate deficiency.
• High white cell count often suggests infection or inflammation, but stress and some medications can raise it too.
• Low platelets can increase bleeding risk and may be related to infections, medicines, or immune conditions.

2) Basic Metabolic Panel or Urea, Electrolytes and Creatinine

What it checks

• Kidney function markers such as creatinine and urea.
• Electrolytes including sodium, potassium, chloride, and bicarbonate, vital for heart rhythm, fluid balance, and nerve function.
• Estimated GFR, a calculated estimate of filtering function, often reported with creatinine.

Why clinicians order it

• To assess dehydration, vomiting, diarrhea, or heat illness.
• To monitor high blood pressure, diabetes, and kidney disease.
• Before starting or while taking medicines that can affect kidneys or potassium, such as some blood pressure tablets and diuretics.
• When there are symptoms like weakness, cramps, irregular heartbeat, confusion, or swelling.

How to prepare

• Fasting is usually not required, but follow your clinician’s instruction if the test is paired with fasting glucose or lipids.
• Maintain normal hydration. Dehydration can raise urea and creatinine and concentrate electrolytes.
• Tell your clinician about supplements especially potassium, creatine, or bodybuilding products, as these can influence measurements.
• Avoid intense exercise the day before if possible, heavy exertion can temporarily raise creatinine in some people.

Common result clues

• High creatinine or low eGFR can reflect reduced kidney function, but also dehydration or muscle mass differences.
• High potassium is urgent when significantly elevated, because it can affect heart rhythm.
• Low sodium can occur with dehydration, overhydration, certain medications, or hormonal issues, and may cause confusion or fatigue.

3) Liver Function Tests, LFT

What it checks

• Enzymes such as ALT and AST, which can rise when liver cells are irritated or damaged.
• Cholestatic markers such as ALP and GGT, which can rise when there is bile flow problem or certain medication effects.
• Bilirubin, related to jaundice and bile processing.
• Proteins such as albumin, which reflects nutrition, inflammation, and liver synthetic capability.

Why clinicians order it

• When there is abdominal pain, nausea, itching, dark urine, pale stool, or yellowing of eyes or skin.
• To monitor chronic conditions, alcohol related harm, fatty liver risk, or hepatitis.
• Before or during certain medicines that can affect the liver.

How to prepare

• Usually no fasting is needed, but some panels are combined with lipids, which may require fasting.
• Avoid alcohol for 24 to 48 hours if you can. Alcohol can increase GGT and affect triglycerides and liver enzymes.
• Tell your clinician about medicines, including paracetamol, anti tuberculosis medicines, some antibiotics, anti seizure medicines, herbal products, and bodybuilding supplements.
• Avoid vigorous exercise just before testing, because AST can rise from muscle strain.

Common result clues

• ALT higher than AST commonly appears in fatty liver and viral hepatitis patterns.
• AST higher than ALT can occur in alcohol related patterns or muscle injury, interpretation depends on context.
• High ALP and GGT can suggest bile duct or gallbladder issues, but ALP can also rise in bone conditions and growth.
• Low albumin can reflect chronic liver disease, kidney protein loss, inflammation, or inadequate intake.

4) Fasting Blood Glucose and HbA1c

What it checks

• Fasting blood glucose measures your blood sugar at one point in time after fasting.
• HbA1c estimates average blood sugar over about 2 to 3 months by measuring sugar attachment to hemoglobin.

Why clinicians order it

• To screen for diabetes or prediabetes, especially with symptoms like increased thirst, frequent urination, blurred vision, slow wound healing, and fatigue.
• To monitor known diabetes and guide medication and lifestyle changes.
• During pregnancy or when there is family history or high risk factors such as overweight, high blood pressure, or high cholesterol.

How to prepare

• Fasting blood glucose needs fasting for 8 to 12 hours, unless your clinician says otherwise. Drink plain water if needed.
• Do not skip your diabetes medicines unless instructed. Ask ahead for a plan if your test requires fasting, especially if you use insulin.
• HbA1c does not require fasting. It can be taken any time of day in most cases.
• Avoid unusual eating patterns the day before. Extreme dieting or bingeing can misrepresent usual control.

Common result clues

• High fasting glucose can indicate diabetes, but can also transiently rise with acute illness, stress, or steroid medicines.
• HbA1c is generally more stable than single glucose readings, but it can be affected by anemia, recent blood loss, or some hemoglobin variants.

5) Lipid Profile, Cholesterol and Triglycerides

What it checks

• Total cholesterol, a broad measure that includes different types of cholesterol.
• LDL cholesterol, often called “bad” cholesterol, associated with artery plaque risk.
• HDL cholesterol, often called “good” cholesterol, associated with protective effects.
• Triglycerides, a type of fat influenced by diet, alcohol, weight, and blood sugar control.

Why clinicians order it

• To estimate cardiovascular risk and guide prevention strategies.
• To monitor response to lifestyle changes and cholesterol lowering medicines.
• In diabetes, high blood pressure, kidney disease, or family history of early heart disease.

How to prepare

• Ask if fasting is required. Some lipid tests can be done non fasting, but fasting is often preferred when triglycerides are important or when your clinician requests it.
• If fasting is required, fast 9 to 12 hours, drink water only, avoid tea with sugar, coffee with milk, juice, and snacks.
• Avoid alcohol for 24 to 48 hours, alcohol can raise triglycerides significantly.
• Keep your usual diet in the days before. A sudden very high fat meal can temporarily raise triglycerides.

Common result clues

• High LDL increases long term risk, treatment decisions depend on overall risk profile and other conditions.
• Low HDL can be improved with activity, weight management, and smoking cessation.
• Very high triglycerides may raise pancreatitis risk, and may be related to uncontrolled diabetes, alcohol, or genetics.

6) Thyroid Function Tests, TSH and Free T4

What it checks

• TSH from the pituitary gland, which signals the thyroid to make hormones.
• Free T4, a main thyroid hormone available for use by the body.
• Sometimes Free T3 and thyroid antibodies are added if autoimmune thyroid disease is suspected.

Why clinicians order it

• Symptoms of hypothyroidism such as tiredness, weight gain, constipation, dry skin, hair loss, and cold intolerance.
• Symptoms of hyperthyroidism such as weight loss, palpitations, tremor, anxiety, heat intolerance, and frequent stools.
• Monitoring thyroid medication dosing.
• Evaluation of menstrual irregularities, fertility issues, or pregnancy related thyroid needs.

How to prepare

• Fasting is usually not required.
• Tell your clinician if you take biotin, a common hair and nail supplement. Biotin can interfere with some thyroid assays. Your clinician may advise stopping it for a period before testing.
• If you take thyroid hormone tablets, ask whether to take your dose before the blood draw or after. Many clinicians prefer testing before the daily dose for consistency, but follow your prescribing clinician’s plan.
• Report pregnancy or recent pregnancy, because normal ranges and targets differ in pregnancy.

Common result clues

• High TSH with low Free T4 often suggests hypothyroidism.
• Low TSH with high Free T4 often suggests hyperthyroidism.
• Normal TSH with symptoms may still require further evaluation, including iron status, B12, vitamin D, sleep, and stress factors.

7) Urinalysis, Routine Urine Test

What it checks

• Dipstick screening for blood, protein, glucose, ketones, leukocytes, nitrites, and pH.
• Microscopy for red blood cells, white cells, crystals, bacteria, and casts if indicated.

Why clinicians order it

• To evaluate urinary tract infection symptoms such as burning, urgency, frequency, and lower abdominal pain.
• To screen for kidney disease or diabetes related kidney involvement.
• To assess dehydration, kidney stones, or blood in the urine.
• As part of pregnancy care or general health review.

How to prepare

• Use a clean container provided by the lab if possible.
• Collect a midstream urine sample. Start urinating into the toilet, then collect urine midstream into the container, then finish in the toilet. This reduces contamination.
• Avoid testing during menstruation if possible, or inform the lab, blood can contaminate the result.
• Do not overhydrate right before collection, very dilute urine can reduce detection of some abnormalities.
• Deliver the sample promptly, ideally within 1 to 2 hours. If delayed, refrigerate if instructed.

Common result clues

• Leukocytes and nitrites can suggest bacterial UTI, but culture may be needed to confirm and choose antibiotics.
• Protein in urine may require repeat testing and quantification, it can reflect kidney disease, fever, heavy exercise, or pregnancy related issues.
• Glucose or ketones may relate to diabetes, fasting, vomiting, or low carbohydrate diets.

8) Urine Culture and Sensitivity, MCS

What it checks

• Identifies bacteria or sometimes yeast in urine.
• Measures antibiotic sensitivity to help select the best antibiotic and reduce resistance risk.

Why clinicians order it

• When a UTI is suspected, especially with fever, flank pain, pregnancy, diabetes, recurrent infections, or treatment failure.
• When symptoms persist despite a negative dipstick or after partial antibiotic use.

How to prepare

• Collect a clean catch midstream sample carefully. Contamination can lead to unclear results or false positives.
• Ideally collect before starting antibiotics. If you already started antibiotics, tell your clinician and the lab, it can reduce bacterial growth and cause false negatives.
• Follow specific instructions for children. Special collection bags or catheter specimens may be needed for accuracy.
• Send the sample quickly to the laboratory, delays allow bacteria to multiply or die off, changing results.

Common result clues

• “Mixed growth” often means contamination from skin flora, a repeat sample may be needed.
• High colony count of a single organism supports infection, especially with symptoms.
• Sensitivity report guides antibiotic choice, do not self select antibiotics without a clinician’s advice.

9) Pregnancy Test, hCG in Urine or Blood

What it checks

• Human chorionic gonadotropin, hCG, a hormone produced in early pregnancy.
• Urine hCG is commonly used for quick screening.
• Blood hCG can detect pregnancy earlier and can be measured quantitatively to help assess early pregnancy progression when clinically indicated.

Why clinicians order it

• Missed period, nausea, breast tenderness, pelvic discomfort, or to confirm pregnancy before certain medications or imaging.
• Evaluation of abdominal pain or bleeding in early pregnancy.

How to prepare

• For urine tests, first morning urine is often more concentrated and may improve early detection.
• Avoid excessive fluids just before urine testing, dilute urine can cause false negatives early on.
• Tell the clinician about fertility treatments, some medications contain hCG and can cause a false positive.
• For a blood test, no fasting is required in most cases.

Common result clues

• A negative test very early does not always rule out pregnancy. Repeat testing may be advised if periods remain absent.
• In early pregnancy concerns, clinicians may order repeat blood hCG levels and ultrasound when appropriate.

10) Stool Tests, Microscopy and Culture, Occult Blood, and Antigen Tests

What it checks

• Stool microscopy for parasites and ova, and white or red blood cells.
• Stool culture for bacterial pathogens in some diarrheal illnesses.
• Occult blood testing to detect hidden blood, used in evaluating gastrointestinal bleeding and screening programs as directed clinically.
• Antigen tests for certain infections, depending on local availability and clinical needs.

Why clinicians order it

• Persistent diarrhea, especially with fever, dehydration, blood in stool, recent travel, or food and water exposure changes.
• Suspected parasitic infection, abdominal cramps, bloating, weight loss, or anemia of unclear cause.
• Investigation of gastrointestinal symptoms or unexplained iron deficiency anemia.

How to prepare

• Use the correct stool container and scoop provided by the lab. Do not use a random jar.
• Avoid contaminating the sample with urine or water. Pass stool into a clean dry receptacle, then transfer using the scoop.
• Deliver the sample promptly. Some tests require same day delivery. Follow the lab’s time and storage instructions.
• Inform the clinician about recent antibiotics, antimalarials, bismuth, or antidiarrheal medicines, they can alter results.
• For occult blood tests, ask about medication and food restrictions. Some protocols require avoiding certain foods or NSAIDs, others use methods less affected by diet. Follow the exact kit instructions.

Common result clues

• Parasites or ova may require treatment and sometimes repeat tests, because shedding can be intermittent.
• Blood in stool needs clinical follow up to identify the source. Causes range from hemorrhoids to inflammation to ulcers.
• Negative results do not always exclude infection, timing and sample quality matter, and multiple samples may be requested.

Extra preparation tips to avoid inaccurate results

• Keep timing consistent for repeat tests. If you monitor a condition, doing tests at similar times of day improves comparability.
• Bring prior lab reports if you are seeing a new clinician, especially if you are a tourist or recently moved.
• Tell the lab about recent imaging with contrast and recent transfusions, these can affect some blood markers.
• Ask if you need to pause supplements such as biotin, iron, or high dose vitamin C. Only pause if instructed.
• For urine tests, avoid vigorous exercise and sexual activity right before sampling if you have previously had blood or protein show up for unclear reasons, your clinician may advise a repeat under controlled conditions.

When to seek urgent care rather than waiting for lab testing

• Chest pain, severe shortness of breath, fainting, or stroke like symptoms require emergency assessment.
• High fever with confusion, stiff neck, severe dehydration, or inability to keep fluids down needs urgent care.
• Blood in urine with pain, inability to urinate, or severe flank pain should be evaluated promptly.
• Severe abdominal pain in pregnancy or heavy bleeding requires urgent assessment.

Frequently asked questions

Can I eat before a blood test?

It depends on the test. Lipid profile and fasting glucose often require fasting, while many other tests do not. If unsure, call ahead. If you accidentally ate, tell the lab and your clinician. Sometimes the test can still proceed, or it may be rescheduled for accuracy.

Can I drink coffee or tea when fasting?

In most fasting protocols, plain water is allowed. Coffee, tea with milk, sugar, or cream, and fruit juice can break a fast and affect glucose and triglycerides. If you need caffeine, ask your clinician whether plain black coffee is acceptable for your specific test, labs vary in policy.

Do lab tests diagnose on their own?

Lab tests provide evidence, but diagnosis usually depends on symptoms, physical exam, medical history, and sometimes imaging. Mild abnormalities are common and may need repeat testing to confirm a trend.

Why are “normal ranges” different between labs?

Reference ranges can differ due to equipment, methods, and the population used to define the range. Always interpret results using the reference range printed on your report and discuss with your clinician.

Can being sick change my results?

Yes. Acute infections can raise white blood cells, affect glucose, and shift electrolytes. Dehydration from vomiting or diarrhea can also change kidney markers. Inform your clinician if you were ill around the time of testing.

Key takeaways for patients in Port Moresby, locals and tourists

• Preparation matters. A small mistake like not fasting or overhydrating can change results and lead to repeat testing.
• Bring your medication list. Include prescriptions, over the counter pain medicines, vitamins, and herbal supplements.
• Ask what the result means for you. The same number can have different meaning depending on age, pregnancy, medical history, and symptoms.
• Follow up. Many tests are most useful when repeated to confirm improvement or progression.

If you need assistance choosing the right test, understanding preparation steps, or arranging laboratory testing alongside general medical care in Port Moresby, Niugini Medical & Diagnostic Services can help coordinate testing and explain what to do next based on your results and symptoms.