{"id":18308,"date":"2026-09-24T00:22:23","date_gmt":"2026-09-23T22:22:23","guid":{"rendered":"https:\/\/www.badania-medyczne.pl\/how-to-prepare-for-blood-tests\/"},"modified":"2026-09-24T00:22:23","modified_gmt":"2026-09-23T22:22:23","slug":"how-to-prepare-for-blood-tests","status":"publish","type":"post","link":"https:\/\/www.badania-medyczne.pl\/en\/how-to-prepare-for-blood-tests\/","title":{"rendered":"How to Prepare for Blood Tests: Fasting, Medicines, Exercise, Sleep and Common Mistakes"},"content":{"rendered":"

Laboratories estimate that most errors affecting test results occur not in the analyser but before sample collection: because of food, coffee, exercise, supplements, a sleepless night or poorly chosen timing. A patient who has not prepared correctly may receive a result that appears to indicate a medical condition but is actually an artefact, or conversely, a result that masks a genuine health problem. Below, we explain how to prepare for the most common blood and urine tests, focusing on factors that actually affect the results. These general guidelines apply at ALAB, Synevo and ETER-MED laboratories; individual laboratories may specify additional requirements for specialised tests.<\/p>\n

What does fasting mean?<\/h2>\n

Fasting means going without food and drinks other than water for 8\u201312 hours. Ideally, have your last meal by 19:00. It should be light, without excessive fat or alcohol. You may drink a glass of still water in the morning; in fact, this is advisable because dehydration concentrates the blood and makes sample collection more difficult. Avoid coffee and tea (even without sugar), juices, chewing gum, cigarettes and lozenges. Fasting for longer than 14\u201316 hours can also affect results: it increases bilirubin and uric acid levels while lowering glucose.<\/p>\n

Tests requiring fasting: Glucose – laboratory test, Insulin – laboratory test, Lipid profile (cholesterol) – laboratory test (cholesterol, LDL, HDL, triglycerides), Iron – laboratory test, liver function tests, phosphorus, uric acid, homocysteine, Vitamin B12 – laboratory test and most hormone tests. Tests that do not require fasting, although consistent preparation is advisable for comparison: full blood count, C-reactive protein (CRP), ESR, Thyroid-stimulating hormone (TSH) – laboratory test, Creatinine – laboratory test, electrolytes, 25-hydroxyvitamin D (25 OH) – vitamin D test, Glycated haemoglobin (HbA1c), antibody tests and serological tests.<\/p>\n

Time of day<\/h2>\n

Many blood parameters follow a circadian rhythm. Iron, cortisol, testosterone, TSH and prolactin levels are highest in the morning; testing in the afternoon may produce values below the reference range even in a healthy person. The standard blood collection window is between 7:00 and 10:00. If tests are being repeated for comparison, samples should be collected at the same time of day.<\/p>\n

Physical exercise<\/h2>\n

Intense exercise within 24\u201348 hours before testing increases CK, Aspartate aminotransferase (AST) – laboratory test, Alanine aminotransferase (ALT) – laboratory test, LDH, Creatinine – laboratory test, uric acid, white blood cells, Ferritin – laboratory test and C-reactive protein (CRP), while lowering haemoglobin through plasma dilution. It can also affect urinary protein levels. The day before testing, walking is fine, but avoid gym workouts and long-distance running. On the day of your test, do not arrive straight from a bicycle ride; sitting quietly for 15 minutes before blood collection helps stabilise the results.<\/p>\n

Alcohol<\/h2>\n

Alcohol consumed within 2\u20133 days before testing increases triglycerides, Gamma-glutamyl transferase (GGT) – laboratory test, Alanine aminotransferase (ALT) – laboratory test, uric acid and MCV, lowers glucose and disrupts electrolyte balance. Avoid alcohol for at least 3 days before a lipid profile or liver function tests; even a single night of heavy drinking the day before can double triglyceride levels.<\/p>\n

Medicines and supplements<\/h2>\n

Do not stop regular medication (for high blood pressure, thyroid disease, diabetes or heart conditions) without consulting your doctor. However, it is worth asking whether to take your medication before or after blood collection. Levothyroxine should be taken after blood has been collected for a TSH test. Guidelines for supplements:<\/p>\n